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eHam Forums => Antennas and Towers and more => Topic started by: AF5C on November 30, 2012, 08:19:07 PM



Title: The Truth: How lossy are traps?
Post by: AF5C on November 30, 2012, 08:19:07 PM
I have seen all sorts of different figures and discussion on how lossy traps are in a yagi.  Where can I find the definitive source to settle this issue for once and all?  Anyone know the truth on this issue?

John AF5CC


Title: RE: The Truth: How lossy are traps?
Post by: W0BTU on November 30, 2012, 09:28:58 PM
From http://www.w8ji.com/traps.htm :
Q:  Do traps create noticeable loss, perhaps one dB per trap typically?

A: NO! Even the worse traps (coaxial traps) in the worse possible condition of operation are only 1.6dB loss for BOTH traps!

Conclusions:

    Trap loss has been greatly exaggerated by advertising hype.


Title: RE: The Truth: How lossy are traps?
Post by: K0OD on December 01, 2012, 08:22:53 AM
Quote
NO! Even the worse traps (coaxial traps) in the worse possible condition of operation are only 1.6dB loss for BOTH traps!

But trap Yagis may have 6 or more of them.


Title: RE: The Truth: How lossy are traps?
Post by: K3VAT on December 01, 2012, 08:42:26 AM
I have seen all sorts of different figures and discussion on how lossy traps are in a yagi.  Where can I find the definitive source to settle this issue for once and all?  Anyone know the truth on this issue?
John AF5CC

John,

W0BTU is correct, both in his conclusion and the creditable reference (W8JI site).  Many high quality and top performing yagi manufacturers (such as Mosley is probably the best example) have been using traps in their antennas for decades.  Just ask someone who has a Pro57 or Pro67.

I've used Unadilla traps for years.  They are well made and inexpensive.  I have three rotary dipoles: 12&17M (uses one pair of 12M traps); 20&30M (uses one pair of 20M traps); and at my old QTH 40&80M (one pair of 40M EURO Design).  I've worked DXCC on all of these bands.  In comparing my trap dipole with a fullsize dipole, performance wise I see no difference.  I also have a 40&80M vertical here using a custom Unadilla trap.

You can order custom-made traps from Unadilla (cost about $20 more).  My 40&80M vertical has a trap resonant at 6.5mhz.  If you're wondering why I chose this you can get the theory behind it at the same website URL as W0BTU noted.

One caveat with using the Unadilla traps: During times when running full power 1.5KW for continuous modes (such as RTTY), one must be careful not to exceed a transmit time of approximately 20 to 30 seconds AND then an off-period of at least the same time (20 to 30 seconds) before retransmitting again.  Forget about a rag-chew on RTTY with full power.

One of the few downsides of traps is limited bandwidth, but this isn't a problem for me as 1) I have a Palstar 2K tuner to touch-up those freqs outside my 1.5:1 SWR, and 2) I operate 95% CW so simply built my dipoles and vertical for that portion of the spectrum.

As pointed out in another one of my postings ... "traps have been given a bad rap, mainly by antenna manufactures who want you to think that their "trapless" contraptions are far superior to any antenna using traps."

GL, 73, Rich, K3VAT


Title: RE: The Truth: How lossy are traps?
Post by: K3VAT on December 01, 2012, 08:45:35 AM
Quote
NO! Even the worse traps (coaxial traps) in the worse possible condition of operation are only 1.6dB loss for BOTH traps!

But trap Yagis may have 6 or more of them.

Do you mean on one element or for the entire frequency coverage of the antenna?  Of course it depends on the number of elements and which elements have traps.  Which trap yagi are you referring to?


Title: RE: The Truth: How lossy are traps?
Post by: AF5C on December 01, 2012, 08:51:33 AM
Any of the common triband yagis like a Cushcraft MA5B.

John AF5CC


Title: RE: The Truth: How lossy are traps?
Post by: WB6BYU on December 01, 2012, 09:08:13 AM
Quote
NO! Even the worse traps (coaxial traps) in the worse possible condition of operation are only 1.6dB loss for BOTH traps!

But trap Yagis may have 6 or more of them.


That doesn't mean you lose 1.6dB in every pair of traps, however.

If you have your power divided among three dipoles in parallel and each
has a 1 dB loss, the total loss is still only 1dB.  That's because each
dipole only handles 1/3 of the power.

It's true that currents are probably higher in a yagi than a dipole,
so you may have 2dB of loss in a 3-element yagi if you had 1.6dB
of loss in a dipole.  But remember that 1.6dB was the worst case,
with coaxial traps (having a lossy capacitor) tuned to resonance
at the operating frequency (as opposed to slightly below it, which
reduces losses.)

By comparison the traps in a common tri-band yagi will have higher
Q capacitors, and lower losses.  A realistic number is probably
around 1dB, depending on the design.


Often the biggest difference in performance between a trap yagi
and a monobander is the compromised element spacings of the
former to get it to work well enough on all three bands.  This can
make more of a difference than the power lost in the traps.


Title: RE: The Truth: How lossy are traps?
Post by: K3VAT on December 01, 2012, 09:41:42 AM
Any of the common triband yagis like a Cushcraft MA5B.  John AF5CC

The Cushcraft MA5B has only ONE pair of traps per element http://www.cushcraftamateur.com/pdffiles/MA-5B.pdf (http://www.cushcraftamateur.com/pdffiles/MA-5B.pdf).  See WB6BYU's posting.

Even the MFJ Cushcraft has traps much more efficient than a coax trap.

73, Rich, K3VAT


Title: RE: The Truth: How lossy are traps?
Post by: M6GOM on December 01, 2012, 09:54:36 AM
Quote
NO! Even the worse traps (coaxial traps) in the worse possible condition of operation are only 1.6dB loss for BOTH traps!

But trap Yagis may have 6 or more of them.

They might but they only have two on each side of the DRIVEN element. Those on the reflector and directors have little effect on loss.


Title: RE: The Truth: How lossy are traps?
Post by: G3TXQ on December 01, 2012, 10:58:29 AM
Those on the reflector and directors have little effect on loss.

Why would that be, when the Reflector and Directors typically flow similar current magnitude to the Driven element?

Steve G3TXQ


Title: RE: The Truth: How lossy are traps?
Post by: K0OD on December 01, 2012, 12:49:59 PM
Quote
"But trap Yagis may have 6 or more of them. "

Let's define our "trap Yagi" for this discussion as being a venerable Mosley TA-33: 3 elements each with two traps, one on each side of the boom.  

Surely a TA-33 would perform somewhat better on say 15 meters if you replaced the trap director and reflector with straight aluminum tubing appropriately tuned for 15. (yes, some tweaking of the trap DE might be required)


Title: RE: The Truth: How lossy are traps?
Post by: WB6BYU on December 01, 2012, 02:13:46 PM
Quote from: K0OD

Let's define our "trap Yagi" for this discussion as being a venerable Mosley TA-33: 3 elements each with two traps, one on each side of the boom.  


Actually (having just repaired my TA-33jr) there are two traps in a single
housing on each side of the boom.  The aluminum trap cover serves as the
radiator between the two traps as well as the capacitor plate for each of
them.


Quote

Surely a TA-33 would perform somewhat better on say 15 meters if you replaced the trap director and reflector with straight aluminum tubing appropriately tuned for 15.



Possibly, but you have to be clear how much of the difference is due to
losses in the trap and how much is due to a different radiator length.

The basic yagi element spacing isn't too bad for 15m.  The late W4RNL
showed that yagi elements can be shortened to 2/3 of full size with
little effect on efficiency (assuming that they have some type of loading
to maintain the proper reactance at the operating frequency.)

But the differences due to element length are NOT a factor of the trap
losses, which is the topic of discussion.  You can model such a yagi
using lossless inductors, then replace them with a realistic model of a
trap to get some sense of the actual difference.

So there really are at least two sets of changes that we see when we
make a trapped yagi:  the performance shift due to changes in the element
lengths and spacings, which are NOT a function of the trap efficiency,
(but rather a shift in the antenna pattern) and the loss of signal strength
due to actual power lost in warming the traps.  Traps are often accused
of having low efficiency due to the former, but only the latter should be
considered. 

That's why I said that the difference in performance between a trap yagi
and a monoband design is due to much more than the trap efficiency.


Title: RE: The Truth: How lossy are traps?
Post by: KH6AQ on December 01, 2012, 05:08:11 PM
Let's think about this. If a pair of traps have loss of 1.6 dB that is 230 watts per trap at 1500 watts RTTY. 230 watts would very quickly smoke any trap. Yet we see triband Yagi-Uda antennas rated for 1500 watts RTTY.

So is 1.6 dB loss per pair of traps a valid number? No.



Title: RE: The Truth: How lossy are traps?
Post by: W6OU on December 01, 2012, 06:51:05 PM
There was a ham (N6NB) who had a crank-up tower mounted on a trailer. He would drive to various ham stations and set up a reference antenna at the same height as the station antenna and measure relative antenna gain. He then compared the relative gains for different station antennas. His main purpose was to compare quad antennas vs yagi antennas but he also made measurements on tri-band trap yagi antennas.  The results were published in one of the ham magazines. He concluded that the trap yagis had a narrower bandwidth so when adjusted for optimum gain in the phone portion of the band, the gain was much poorer in the cw portion.


Title: RE: The Truth: How lossy are traps?
Post by: G3TXQ on December 02, 2012, 01:19:33 AM
Please let's not mis-apply W8JI's figures!

His loss figure of 1.6dB applies to a pair of RG58 coaxial 40m traps operating at resonance, for which he measured Rp as 17,800 Ohms; compare that to the Rp of 140,000 he measured for HyGain 10m and 15m traps!

The 1.6dB figure is not really relevant to the discussion unless you're going to build a Yagi using RG58 coaxial traps.

Steve G3TXQ





Title: RE: The Truth: How lossy are traps?
Post by: W2ANZ on December 02, 2012, 10:04:40 AM
I thought the loss at the parallel resonance frequency of the trap was not the issue.  I thought it was the loss at the lower bands where the trap just acts as loading.... loading = lower radiation resistance = higher resistive losses.  This applies more to trapped vertical antennas, not Yagis.


Title: RE: The Truth: How lossy are traps?
Post by: WB6BYU on December 02, 2012, 11:33:34 AM
Quote from: W2ANZ
I thought the loss at the parallel resonance frequency of the trap was not the issue.  I thought it was the loss at the lower bands where the trap just acts as loading.... loading = lower radiation resistance = higher resistive losses.  This applies more to trapped vertical antennas, not Yagis.


That's part of the confusion:  if one antenna has less gain than another, it
is because it uses traps, it is shorter than full sized, or some other reason?
If you are discussing "lossy traps", then you have to compare an antenna
of similar size that uses some form of loading other than traps, in which
case the difference due to the antenna not being full sized doesn't enter
into the equation.  So you need to be very clear whether you are comparing
traps to some other form of loading, or a trapped antenna to a monobander.
(Both are interesting comparisons, but this thread was specifically about
"how lossy are traps.")

A yagi designed for maximum gain often has a low radiation resistance, meaning
that current is higher than in a dipole.  Thus trap losses can actually be higher
than in a trap vertical.

The voltage across the trap is highest at resonance, which is where the
losses will be highest due to high circulating currents.  Designing a trap
antenna with the trap resonant just below the band where it needs to
act as a trap reduces losses, but it also complicates the design somewhat
because the outer sections still affect the tuning to some extent.  The
further the trap is from resonance, the more current flows in the antenna
beyond the trap.

Many antennas that claim "NO LOSSY TRAPS" use instead some even lossier
substitute, such as self-resonant coils ("Iso-Res Inductors") that act like a
trap due to the parasitic capacitance of the coil rather than an intentional
capacitance added across it.  Traps made using linear loading tend to have
slightly higher losses than those using standard coils.

The reason that W8JI's value of 1.6dB for coax traps is not typical of most
commercial offerings is that the loss is due to the poor Q of the coax
used as a capacitor.  The traps in my TA-33jr use mostly air dielectric
(with some plastic spacers) and will be considerably more efficient.
(Unless the antenna comes down in an uncontrolled manner after Field
Day and breaks one of the connecting wires...)


True, there is some loss in performance due to a shorter element, but that
is the case whether one uses a trap or a loading coil.  Actually, performance
is pretty reasonable down to about 60% of full size, after which the losses
accelerate as it gets shorter.

Because the traps are a combination of L and C, the bandwidth of a trapped
antenna will be less than that of one using just loading coils, but there
otherwise might not be much difference in performance.


Title: RE: The Truth: How lossy are traps?
Post by: N8CMQ on December 02, 2012, 01:43:45 PM
 Your question is a good one!
Unfortunately, it does not have a simple answer...
The best answer tho, is not enough loss to worry about,
unless inferior materials are used to construct the trap.
 
 Look at what a trap is composed of, a coil and a cap.
Many early trap antennas used a transmitting cap and
coil in their construction. Somewhere along the line,
someone used coax to form the cap, someone else made
the coax into the coil and the cap.
  Antenna manufacturers made traps out of coils
and sections of tubing to make an air dielectric cap.

 Other antenna manufacturers started the 'claims' wars.
Claims like, antennas with traps are lossy, have narrow bandwidth, or
whatever they wanted to say to make their antennas seem better.
 
 Unfortunately, many of the negative claims have taken on
the LAW of TRAP ANTENNA status. It really is too bad, as
many antennas have traps and work very well, and have
good bandwidth.
 
 As far as traps go, they work the same in a vertical as a Yagi.
A Yagi just happens to have two traps as they have two elements,
where a vertical has one trap operating over a ground plane.
 
 Another problem with a trap Yagi, the element spacing is best for
one band and a compromise on the other bands. However, the
antennas do work, and many hams have used them for years
and have been happy with them.
 
 Vertical antennas also work very well with traps.
I have a 4BTV with an 80M resonator on top. The SWR is good
for all four bands, 10M to 40M, while the 80 meter resonator is
a narrow slice of the phones band.
 
 If you need to have a multi-band antenna, don't worry about
the traps, worry about the materials used to make the antenna.
Read comments from people who own and use the antennas, as well.


Title: RE: The Truth: How lossy are traps?
Post by: K2TL on December 03, 2012, 10:25:15 AM
I'm almost certain the ARRL did a study of trap loss in their lab.  I still see references to this study in QST from time to time, like in "The Doctor is In" articles and such.  The ARRL found that even the best traps lose 1.5 db.  A multiband trap antenna can result in quite a bit of loss depending on how many traps RF needs to travel through. As the ARRL does not manufacture antennas,  I would say they do not have a biased opinion.  They have plenty of publications on the use and construction of traps.  As long as you are willing to accept the loss, traps can be very convenient.  But if you can avoid them you might as well.


Title: RE: The Truth: How lossy are traps?
Post by: G3TXQ on December 03, 2012, 12:01:10 PM
I'm almost certain the ARRL did a study of trap loss in their lab.  I still see references to this study in QST from time to time, like in "The Doctor is In" articles and such.  The ARRL found that even the best traps lose 1.5 db. 

That's a much higher figure than I've seen quoted from other reputable sources, unless we are talking about very poor quality traps made from lossy coaxial cable.

An ARRL periodical search threw up nothing; can you point us to a reference?

73,
Steve G3TXQ


Title: RE: The Truth: How lossy are traps?
Post by: WB6BYU on December 03, 2012, 12:43:25 PM
Quote from: K2TL
...The ARRL found that even the best traps lose 1.5 db...


I have a pretty good memory for antenna articles, and I don't ever
remember seeing this in QST, either a full article or even referenced
in the text of another article, at least not in the last 40 years.  I'd
want to see the original article and evaluate their measurement
technique to see what they were actually measuring.


But let's do a quick analysis:  1.5dB means 30% of your power is
lost in the trap.  At 1kW that is 300 watts.  Even if we allow this
for a pair of traps, that means each trap would be dissipating 150
watts.  That certainly would make the trap warm to the touch, as
anybody who has tried to grab a hot lightbulb will know.

I have an old electric heater with 10 curly wires in the element:
a single wire gets hot enough to glow at 100 watts.  That seems
a bit high for a single trap.


Title: RE: The Truth: How lossy are traps?
Post by: AA4PB on December 03, 2012, 12:51:21 PM
In addition, a 3 ele triband Yagi would have a hard time producing any measured gain over a dipole if each trap added 1.5dB of loss.


Title: RE: The Truth: How lossy are traps?
Post by: K2TL on December 03, 2012, 01:07:34 PM
Best I can recall, I think I saw a reference to this study in QST within the last  few months.  I don't keep my old magazines anymore so I can't dig through them.  I'm pretty sure it was mentioned in "Doctor is In".. Someone wrote in about traps versus monoband antennas, or something like that.  I have read references to this study several times, but never the actual report itself.  I'll try and dig it up.


Title: RE: The Truth: How lossy are traps?
Post by: AA4PB on December 03, 2012, 01:22:57 PM
I could believe that the difference in gain on 20M between a 3 ele monobander and a 3 ele tri-band trapped Yagi is 1.5dB. Thats a whole lot different than saying that a trap has 1.5dB of loss. Trapped tri-banders are a compromise in a several ways including trap loss and element spacing.


Title: RE: The Truth: How lossy are traps?
Post by: W0BTU on December 03, 2012, 01:25:23 PM
Quote from: K2TL
...The ARRL found that even the best traps lose 1.5 db...

But let's do a quick analysis:  1.5dB means 30% of your power is lost in the trap.  At 1kW that is 300 watts.  Even if we allow this for a pair of traps, that means each trap would be dissipating 150 watts.  That certainly would make the trap warm to the touch, as anybody who has tried to grab a hot lightbulb will know.

I have an old electric heater with 10 curly wires in the element: a single wire gets hot enough to glow at 100 watts.  That seems a bit high for a single trap.

In addition, a 3 ele triband Yagi would have a hard time producing any measured gain over a dipole if each trap added 1.5dB of loss.

Precisely. These are words of wisdom from two wise people who have stopped to think about what a dB really is (watts and enough heat to destroy the trap), instead of just echoing yet another useless and harmful belief.

It doesn't take very much common sense at all to figure out that this myth is a bunch of utter nonsense. It was likely started by people trying to sell trapless antennas, so people would spend their money on their antenna instead of their competitor's antennas with traps that worked just fine for what the buyers needed to get a decent signal radiated.

"All traps have enough loss to matter" is simply a myth that just refuses to die, because countless people just keep repeating what they hear and read over and over and over like a broken record instead of using their brain. :-)


Title: RE: The Truth: How lossy are traps?
Post by: K2TL on December 03, 2012, 03:01:44 PM
I agree 1.5 db seems high, and I might be mistaken as to what the ARRL actually measured.  I have read different versions of it.  I wish I could find the original study.  I guess I'll have to make it my life's mission to find it.  When I first read the reports on it, it was depressing because I had really never troubled over trap loss.  Now it has become a big deal as many of the antenna manufacturers hawk "No Lossy Traps!", leading one to believe that trap loss is an issue. The ARRL web site is a misery to try and find old articles.  The previous version was simple.  I can't find anything there now.
Nothing is 100% efficient, including traps.  I suppose there might be some truth to the trap loss drama.  How much depends on what you want to believe or who you listen to?


Title: RE: The Truth: How lossy are traps?
Post by: K3VAT on December 03, 2012, 04:03:28 PM
I agree 1.5 db seems high, and I might be mistaken as to what the ARRL actually measured.  I have read different versions of it.  I wish I could find the original study.  I guess I'll have to make it my life's mission to find it.  When I first read the reports on it, it was depressing because I had really never troubled over trap loss.  Now it has become a big deal as many of the antenna manufacturers hawk "No Lossy Traps!", leading one to believe that trap loss is an issue. The ARRL web site is a misery to try and find old articles.  The previous version was simple.  I can't find anything there now.
Nothing is 100% efficient, including traps.  I suppose there might be some truth to the trap loss drama.  How much depends on what you want to believe or who you listen to?

As this is a technical forum we need to have all of our references clearly designated and available for others to examine.  That 1.5db number seems to be drawn straight out of the hat - I'm sorry, it is meaningless as it is undocumented.  What was documented was posted early on: the W8JI trap study.  We need to go by this unless someone can show another creditable study.

...  How much depends on what you want to believe or who you listen to?

Let's replace myth and hype with solid technical empirically-based knowledge.  IMHO, part of the problem lies in 1) propagating hearsay and this includes biased claims by manufacturers and others mainly concerned with their own self-interest; and 2) not understanding basic laws of radio communications.  73, Rich, K3VAT


Title: RE: The Truth: How lossy are traps?
Post by: K2TL on December 04, 2012, 01:58:07 AM
OK Rich.  I did not know you were the moderator of this thread and made up the rules. However, I did clearly say that it was just something I had read from time to time, as a reference, and not the whole report.  If this offends you, then maybe you can do some deep breathing meditation and try and calm down.
You can pick up any issue of QST and see antenna manufacturers claiming better efficiency antennas due to "no lossy traps".  I did not pull that out of my hat either.
You are free to accept what you like, documented or not.  Same as everyone else.  Personally, I have used traps over the last 48 years and I don't have a big problem with their performance.
The 1.5 db claim is something I read regarding an ARRL study.  That's the end of it.


Title: RE: The Truth: How lossy are traps?
Post by: G3TXQ on December 04, 2012, 02:46:15 AM
I just ran a quick EZNEC model of a 20m/15m trap dipole with different Q values for the trap inductors. These were the losses per trap at 21MHz:

Q=300, trap loss = 0.04dB
Q=200, trap loss = 0.08dB
Q=100, trap loss = 0.16dB

To get a total loss of 1.6dB for the two traps, I had to drop the Q to 15; to get a loss of 1.6dB for each trap I had to drop the Q to 4.

73,
Steve G3TXQ



Title: RE: The Truth: How lossy are traps?
Post by: K2TL on December 04, 2012, 05:13:28 AM
I would like to see what kind of trap the ARRL used in the study.  I guess it was some kind of crap.  Or maybe those who have quoted the study, and I had the misfortune of reading, did not represent the findings well.
Years back the ARRL prohibited antenna advertising to show gain in db.  They claimed that those figures could be misleading and they did not want to be a party to it.  So you will notice that all gain figures are never shown in a QST ad.  However, I see that they do allow "No Lossy Traps" in their ads.  Thinking about this, I concluded that the ads never really say that traps are lossy.  They just say that their antennas do not include lossy traps.  Kind of sneaky and causes one to infer that traps are lossy.


Title: RE: The Truth: How lossy are traps?
Post by: KE2TR on December 04, 2012, 09:04:27 AM
In real world experience's even a HyGain TH7/TH6 which does have some monoband/semi monoband parasitic elements plus proper spacing between these elements for the three different bands you still have the loss on the 4 or 8 traps used in the driven elements. The KLM KT34 design uses linear loading with decoupling caps that although might have lesser losses but its still a form of a trap. Real world gain of these big triband beams maybe might be more like 3-4 db over a dipole at the same height above ground compared to a two element monoband beam's 4.7 db. This is one of the things that made the Force 12 C3 series tribanders do so well but a two element beam doesn't have the same FB ratio but the gain is better. The white papers on tribanders gave a good look at what some of the bigger tribanders don't do. Also look at the way the feed system is used on some of these larger tribanders with more losses than you think, simple is better. Over the years I have owned beams like Mosley's CL33 then upgraded to a TH6 then TH7, between these beams there was some improvement's but when I place a C12 C3E at the same spot I had the TH7 the gain was far better, the antenna heard better, TX was better, the only area the Hy Gain was better was FB and the C3 was so much lighter on the tower. I then when to monoband beams and although they performed better in a/b comparisons that little C3 held its own against a 4 element monoband 20mtr beam, comparo's done then only showed 3db at the other station s meter on most dx contacts. The stepper antennas do well on 20 and 17mtrs but as you get past 15mtrs and up there spacing is a little long for the higher bands when you look at there 4 element beam.
Bottom line from what I have seen in real world use traps do rob the real gain of an antenna, trapped antennas do work but, they have FB and some form a pattern but the real forward gain which is why you want a beam is lower. It really depends on what you want.


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 16, 2012, 11:36:21 PM
I helped a Ham friend replace a Hy Gain TH 6 trapped tribander, with a stack of 3 Hy Gain 3 element Monobanders for 10, 15, and 20.
To say both he and I were disappointed is putting it mildly! Of course, because we read all the bullshit about how much traps were "costing us", we had high expectations for the 3 full size Hy Gain Monobanders vs the Trapped Hy Gain TH 6.
After a LOT of hard work (and my friends considerable cash outlay), we found out the truth for ourselves. Traps are not "that bad", and common sense should have told us that, since so many Hams use trapped tribanders.
Perhaps if we had went to 4 or 5 element Hy Gain monobanders, they would have convincingly kicked the Hy Gain TH 6's azz ? But we found very very little difference between the stack of 3 element Hy Gain Monobanders vs the Trapped Hy Gain TH 6.

WE put in a call to Hy Gain Engineering, located in Lincoln Nebraska at that time, to tell them of our findings. The Hy Gain Antenna Engineer we talked to that day said he wished we would have called him first, before we wasted all that money!

He told us he would have suggested we went to the Hy Gain 204 (4 elements on 20) and 5 element Hy Gain Long John Yagi's for 10 and 15. He said, in a nice way, it was foolish of us to try and "take out" the well designed Hy Gain TH 6,  with only a stack of 3 element monobanders!

He offered to mail or fax us measurements of the Hy Gain TH 6 on each band, made on Hy Gains full size antenna range, as well as measurements for Hy Gains 3 element monobanders, so we could compare them vs the Hy Gain TH 6's measurements.

The antenna range measurements he sent us confirmed what we found in on the air use.

Now, if  a stack of Hy Gain full size trapless 3 element monobanders will not take out a TH 6, then how in the hell is a 2 element Force 12 going to beat, much less equal, a TH 6.

The answer is, it isn't.

I was lucky, I "learned my lesson" nearly 30 years ago, not to believe the advertising that makers of trapless antennas would Like for you to believe.

That Hy Gain engineer was a fellow Ham ( I can't remember his call). He told us that making a no trap antenna was a "piece of cake", vs making one with traps.

He told us that Hy Gain actually TESTED every no trap antenna. In fact, he assured us that Hy Gain actually bought and tested EVERY competitors product, that competed with their "bread and butter" antenna, the Hy Gain TH 6, Trap or no trap.

He even offered to send us the antenna range test results, to see what he already knew.













Title: RE: The Truth: How lossy are traps?
Post by: WB6BYU on December 17, 2012, 08:59:18 AM
The TH-6 has a couple advantages over some of the smaller triband yagis:

1) it is longer, so the elements have proper spacing on 20m.
2) it has 4 elements on 10m
3) It has fewer traps per element.  The only element that functions on all
three bands is the driven element.  Using a total of 6 various element allows
more optimum spacing of the elements for each band, including two elements
with no traps at all.  (Note that this does NOT mean it functions as a 6-element
yagi on any band.)

But if anything these point out the compromises of a "typical" tribander with
only 3 physical elements, each used on all three bands.  That makes more
difference in final performance than the use of traps.


Title: RE: The Truth: How lossy are traps?
Post by: AA4PB on December 17, 2012, 09:51:09 AM
Even with the steppir, while the element lengths are adjustable the element spacing is not so it is still a compromise.


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 17, 2012, 08:24:44 PM
The TH-6 has a couple advantages over some of the smaller triband yagis:

1) it is longer, so the elements have proper spacing on 20m.
2) it has 4 elements on 10m
3) It has fewer traps per element.  The only element that functions on all
three bands is the driven element.  Using a total of 6 various element allows
more optimum spacing of the elements for each band, including two elements
with no traps at all.  (Note that this does NOT mean it functions as a 6-element
yagi on any band.)

But if anything these point out the compromises of a "typical" tribander with
only 3 physical elements, each used on all three bands.
  That makes more
difference in final performance than the use of traps.
Exactly! One poster made an observation that a 2 element Force 12 tribander was as good on the air, or possibly better, then a TH 7 in this thread !

OK, Traps do have some loss, but so does a bunch of 2 element full size antennas, on the same boom!
It is true, that with careful computer modeling, an interlaced Yagi can minimize these losses, but they are still there.
This is a fact that the makers of these trapless Yagi's  seldom admit, as they bad mouth trapped Yagi Designs.





Title: RE: The Truth: How lossy are traps?
Post by: W6GX on December 18, 2012, 01:06:18 AM
OK, Traps do have some loss, but so does a bunch of 2 element full size antennas, on the same boom!
It is true, that with careful computer modeling, an interlaced Yagi can minimize these losses, but they are still there.

Please elaborate on your statement.  Loss = RF energy which has been converted to heat.  Your statements says a trapless antenna has loss.  What part of the trapless antenna is RF energy converted to heat?

73,
Jonathan W6GX


Title: RE: The Truth: How lossy are traps?
Post by: NH7O on December 18, 2012, 08:39:19 PM
I helped a Ham friend replace a Hy Gain TH 6 trapped tribander, with a stack of 3 Hy Gain 3 element Monobanders for 10, 15, and 20.

Those Hy Gain monobanders have pretty short booms. They really don't have the gain that you would expect from an actual full size 3 element.


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 19, 2012, 07:29:48 AM
OK, Traps do have some loss, but so does a bunch of 2 element full size antennas, on the same boom!
It is true, that with careful computer modeling, an interlaced Yagi can minimize these losses, but they are still there.

Please elaborate on your statement.  Loss = RF energy which has been converted to heat.  Your statements says a trapless antenna has loss.  What part of the trapless antenna is RF energy converted to heat?

73,
Jonathan W6GX
Next time, try reading the whole thread ?


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 19, 2012, 08:12:18 AM
I helped a Ham friend replace a Hy Gain TH 6 trapped tribander, with a stack of 3 Hy Gain 3 element Monobanders for 10, 15, and 20.

Those Hy Gain monobanders have pretty short booms. They really don't have the gain that you would expect from an actual full size 3 element.
Yes, but they certainly have more gain then then the interlaced 2 element Force 12 antenna being touted in this thread by a Ham as being "better" then a Hy Gain TH 7.
I have zero "problems" with the Force 12 triband antennas.
Their full sized, interlaced, non trapped elements, are one design approach to making a triband beam antenna.
But, to think that traps have so much loss, that a trapless 2 element Force 12 tribander, can equal, or even approach a trapped Hy Gain TH 6 or a Hy Gain TH 7  IMHO is mental masturbation.
The Bigger Hy Gain Thunderbirds will tear the little Force 12's a new azz, in the pileups.

Now, IF you want to compare a 2 element trapless Force 12 tribander against a smaller 3 element trapped Cush Craft A3 or Hy Gain TH 3, you MIGHT have a case.
I say MIGHT, because if you are a 2 element trapless Force 12 owner, you are still up against 3 Elements vs 2, if you compare your antennas against a CushCraft A3, or a Hy Gain TH 3.
So, the QUESTION is this - Can a 2 element non trapped, interlaced full size tribander, compete with a 3 element trapped tribander ?




Title: RE: The Truth: How lossy are traps?
Post by: WB6BYU on December 19, 2012, 08:39:17 AM
Quote from: KA7NIQ

So, the QUESTION is this - Can a 2 element non trapped, interlaced full size tribander, compete with a 3 element trapped tribander ?



Of course they can compete.  They may always end up at the bottom of the league
standings, but occasionally they might still win a game under certain circumstances.


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 19, 2012, 08:55:26 AM
Quote from: KA7NIQ

So, the QUESTION is this - Can a 2 element non trapped, interlaced full size tribander, compete with a 3 element trapped tribander ?



Of course they can compete.  They may always end up at the bottom of the league
standings, but occasionally they might still win a game under certain circumstances.
LOL, u are 2 funny!
Hey, one day I saw a contester bragging about his new Force 12 Tribander!
I knew he used to have a Hy Gain TH 7.
I asked him if he really thought the Force 12 was better ?
He told me the Force 12 was more "amplifier friendly"
IOW, it would easily accept the output from his 3 hole 8877 Amp more better.


Title: RE: The Truth: How lossy are traps?
Post by: W6GX on December 19, 2012, 12:11:02 PM
To help answer the question posted by the original poster 'how lossy are traps' below are the specs from a well-known trapped antenna.  If one is wondering how many watts and how much heat is lost via the traps, one could do an experiment by running 1.5kw into the antenna and measure the amount of heat generated by each trap.  On a trapless antenna there's no need to de-rate the power handling for high-duty cycle modes.

 Power Rating, watts CW
    2500
Power Rating, watts SSB
    5000
Power Rating, AM/FM
    600
Power Rating, RTTY/AMTOR
    600

Now let's examine the effects of element count in a yagi.  With a dipole you get 0dbd.  Add a parasitic element you'd get about a 4dbd of gain.  Then you double the boom length and add a third parasitic element.  You'd get one additional db of gain.  As you add more elements you get diminishing returns.  In summary the bulk of gain in a yagi comes from the first two elements.  In summary, the two-element is a fine choice for many as the antenna footprint is 1/2 of a three-element.

73,
Jonathan W6GX


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 19, 2012, 09:36:49 PM
Good Post Jonathan.
It seems every Ham has their own opinions on how damaging, or not,
 Traps really are, as far as loss goes.
I have to admire the excellent sales job done by Force 12, supporting their design approach (No Traps). LOL, they really "put the fear of God" in many Hams about the loss "inherent in a triband beam" that uses traps.
I have only been a Ham for 27 years, a short time, compared to many.
But I never recalled any of us Hams being worried, as some are now, about Trap Loss.
All our triband yagi antennas had traps, and we pretty much accepted it.

Putting aside the loss question about the use of traps in a triband beam, lets look for a minute at what happens if we choose not to use traps.
WE get more windload for one, because of all the extra elements. Then, the full size elements are considerably longer, important to some of us on small city lots.
Then, there is the automatic interaction we get, by having several different antennas, all on the same boom, in an interlaced design.
How MUCH interaction, and it's effect on performance, is beyond my limited technical capability. We will have to ask some really smart Antenna Elmers, like W8JI, etc, etc.
I understand that with careful computer modeling, this interaction can be minimised, but never completely eliminated.

It sort of surprised me, that none of the trapped tribander antenna makers like Mosley, Hy Gain, or Cush Craft, confronted all the possibly misleading claims of Force 12, and the other Non Trap Triband Beam makers.

You know what they say ? Tell a big enough Lie often enough, and with no counter argument, it becomes "Truth" !













Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 20, 2012, 12:48:31 AM
Trap Loss, or lack of it, in triband beam antennas, has always been a subject I have wondered about.
I just Googled "Trap Loss W4RNL" to see what he had to say about this matter of interest to me.

Check it out

The Effects of Traps on Beams

Experience has shown that the losses in gain of center loaded elements are additive, at least in 2-element Yagis. If this experience holds true of the 14.1 MHz elements with 15-meter traps, then one might expect about 0.5 dB loss of forward gain relative to a full size Yagi of the same design but unloaded.

To test this hypothesis, I scaled a 10-meter beam with a 50-ohm feedpoint impedance for 14.1 MHz. The new full-size beam spaced the elements by 12.12', again using 1" aluminum tubing for modeling simplicity, as shown in Figure 3. With a driven element 32.2' long and a reflector 34.94' long, the beam achieved its maximum front-to-back ratio (10.68 dB), a figure almost exactly that of its 10-meter counterpart. The resonant feedpoint impedance was 50.7 ohms. The forward gain under these condition was 6.13 dBi.


If a beam using two trapped elements could be constructed with a comparable maximum front-to-back ratio and a comparable feedpoint impedance, then the gain difference between it and the full size beam would be a good measure of gain reduction due to the shortening and other losses imposed the traps. In fact, such a beam was modeled, using the same element spacing. The driven element was 27.06' long, and the reflector was 27.7' long. The 15-meter traps were left in their original positions. It is possible that positioning the traps as they might be in a 2-band trap beam could alter the 20-meters values slightly, but the alteration was judged unlikely to be significant.

The maximum front-to-back ratio of the 14.1 MHz beam with 15-meter traps was 10.68 dB, while the feedpoint impedance was 50.5 ohms. Under these control parameters, the forward gain was 5.64 dBi. (Note: for all the 2- element beams modeled here, higher forward gains are certainly possible, but at reduced front-to-back ratios.) The gain difference between the full size Yagi and the version with 15-meter traps is 0.49 dB.


Models of tri-band beams with 3 or more elements and/or more than 2 traps per element will follow the same procedure used here for these simplified models. Data for each trap will be needed for calculations of appropriate parallel R-L-C values. Also need will be a precise element diameter schedule, along with the exact location of the traps. Although time-consuming, such modeling projects should be quite straightforward.

Conclusion

If the technique of modeling traps is sound, then their presence does occasion some loss in forward gain relative to trapless antennas of comparable design, at least for frequencies lower than the resonant trap frequency. How significant this loss may be is a judgment requiring the examination of factors in addition to those included in the modeling exercise. Models also suggest that at frequencies for which the traps represent resonant terminations, gain will be very similar to that of trapless versions of the antenna.

Whatever the gain situation, the exercise does demonstrate that traps can be modeled effectively as parallel R-L-C loads for each frequency of interest.



So, if W4RNL is correct, and he quite often was, then trapped multiband beam antennas DO have about 1/2 db of Loss.
The question then becomes, how much, and what kinds of penalties does one have to pay, in a non trapped multiband beam antenna, for the electrical interaction between all those full sized elements.
Does Gain, Bandwidth, or Rejection (pattern) suffer, in a non trap multiband yagi, and if so, how much ?

Then, we have increased size (longer elements) and windload in the full size non trapped and interlaced multiband Yagi.

I think what CAN be safely said, in all of this, is that any Triband Yagi, trapped or full size non trapped, is a compromise antenna, vs a full size Monoband Yagi, of equivalent boom length.











Title: RE: The Truth: How lossy are traps?
Post by: W6GX on December 20, 2012, 01:14:45 AM
The question then becomes, how much, and what kinds of penalties does one have to pay, in a non trapped multiband beam antenna, for the electrical interaction between all those full sized elements.
Does Gain, Bandwidth, or Rejection (pattern) suffer, in a non trap multiband yagi, and if so, how much ?

Then, we have increased size (longer elements) and windload in the full size non trapped and interlaced multiband Yagi.

The answers to these questions can be found here:  http://www.championradio.com/HF-TRIBANDER-PERFORMANCE-TEST-METHODS-RESULTS.2.  The book is copyrighted and thus I cannot post the answers here.  The book contains test data (i.e. facts) and no marketing materials.  The book is invaluable for anyone in the market for a tribander.

If you have enjoyed the book then the next book on my recommended list is this one:  http://www.championradio.com/ARRAY-OF-LIGHT-Straight-talk-about-antennas-and-related-subjects-Third-Edition.113.

73,
Jonathan W6GX


Title: RE: The Truth: How lossy are traps?
Post by: G3TXQ on December 20, 2012, 03:08:48 AM
The maximum front-to-back ratio of the 14.1 MHz beam with 15-meter traps was 10.68 dB, while the feedpoint impedance was 50.5 ohms. Under these control parameters, the forward gain was 5.64 dBi. (Note: for all the 2- element beams modeled here, higher forward gains are certainly possible, but at reduced front-to-back ratios.) The gain difference between the full size Yagi and the version with 15-meter traps is 0.49 dB.

Note that not all the 0.49dB gain difference is attributable to dissipation in the traps - about 0.34dB is, the rest is attributable to the changed geometry.

Also note that Cebik assumes a trap Q of 126 for his model.

73,
Steve G3TXQ


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 20, 2012, 03:57:18 AM
The maximum front-to-back ratio of the 14.1 MHz beam with 15-meter traps was 10.68 dB, while the feedpoint impedance was 50.5 ohms. Under these control parameters, the forward gain was 5.64 dBi. (Note: for all the 2- element beams modeled here, higher forward gains are certainly possible, but at reduced front-to-back ratios.) The gain difference between the full size Yagi and the version with 15-meter traps is 0.49 dB.

Note that not all the 0.49dB gain difference is attributable to dissipation in the traps - about 0.34dB is, the rest is attributable to the changed geometry.

Also note that Cebik assumes a trap Q of 126 for his model.

73,
Steve G3TXQ
Hi Steve! Good to see you over here! Where do you stand on the Trap Loss Debate ?
I know you do a considerable amount of computer modeling. Is it not also true that any non trap interlaced Yagi for 3 or more bands will have some element interference that may effect it's performance ?


Title: RE: The Truth: How lossy are traps?
Post by: G3TXQ on December 20, 2012, 07:27:08 AM
Hi Steve! Good to see you over here! Where do you stand on the Trap Loss Debate ?

Obviously, real traps dissipate power as heat; but with well-designed traps it's nothing like the loss that "trapless antenna" advertising copy would have us believe.

Folk seem to be forgetting that even a monoband Yagi is a "compromise" antenna: it's a compromise between Gain, F/B, F/S and a feedpoint impedance that can be efficiently matched!

73,
Steve G3TXQ


Title: RE: The Truth: How lossy are traps?
Post by: WB6BYU on December 20, 2012, 09:15:21 AM
And don't forget operating bandwidth, for all of those parameters.

You have to be very careful comparing antennas, because sometimes the parameters that
seem most important really aren't the ones that determine effectiveness.

Gain is a good example:  yes, gain is good, as it makes our signal stronger.  But does
that parameter represent the peak gain at some point in the band, or the average gain
across the band?

F/B can be even more misleading:  I've built antennas with a claimed 50dB F/B ratio, and
they might actually meet that spec at one frequency on 2m.  But 500kHz away it might
only be 20 or 25dB, and less than that at the band edges.  And that presumes you are
measuring a null exactly off the back of the antenna - a more useful figure often is the
Front to Rear ratio, which averages the signal strength across the rear hemisphere of
the antenna.  A beam with a cardiod pattern may have a very sharp rear null but not be
as good at reducing interfering signals that come from 30 degrees off the back.

Reasonable 2-element yagis typically run around 6dBi gain and 10dB F/B ratio.  I've built
them with 30dB F/B ratio by using much shorter spacings (5" to 6" on 2m, or 4' to 5' on
20m.)  But the F/B ratio might only be 10dB at the band edges, and the F/B will vary
as the elements blow in the wind due to the very close spacing.

2-element beams with straight elements only have 3 effective variables for adjustment:
the lengths of each element and the spacing between them.  This makes it difficult to
try to optimize gain, F/B, resonant frequency, and feedpoint impedance at the same
time, because every change to one thing affects something else.  A 3-element yagi has
5 variables, making it easier to find a combination that meets the requirements an all
4 categories.

Trapless combinations aren't always easy to design and maintain, however, due to the
interactions among the elements.  This is more of a problem with 2-element designs
due to the limited range of adjustments.  W4RNL put a lot of work into trying to develop
a design for nested Moxon beams for multiple bands.  Antenna performance depends on
the mutual coupling between the elements, and adding extra bits will change that.
And as you add more elements the wind loading increases.

That's not to say that 2-element yagis don't have their place:  certainly the many
users of Moxons and Hex Beams have shown that it is sometimes easier to get a light
antenna up higher than a larger / heavier one, and the increased height (or the ability
to put up an antenna at all) will more than make up for lower gain.  I've assembled my
TA-33jr with just 2 elements before for this reason (and sometimes use the driven
element alone as a dipole) when I was concerned about wind loading.  For Field Day or
other portable operation, having something that is small and light is very convenient:
we put up the TA-33jr easily enough with 2 or 3 people, but, while I have the parts for
two TH6s in my barn, one look at the size of the boom (and the required truss to support
it) immediately eliminates any thought of using those.


So I don't think the real world is as polarized as the debate sometimes makes it seem.
Yes, traps have some loss, and that can be reduced by using high Q traps and/or by
designing the antenna so the traps are resonant slightly off of the operating frequency.

Multiband antennas that don't use traps may be more complex in other ways.  One
disadvantage of traps is that something can break inside the trap and not be as easy
to see on a quick review (especially if the antenna came down at the end of the last
Field Day in a rather... umm... uncontrolled manner.)

Sometimes an antenna that is lighter or has less wind loading is a better choice if it
allows the use of a smaller mast, is easier to put up, or can be put up higher than
a heavier antenna would.  Other times a full-sized antenna gives enough performance
improvement that it is worth the upgrade.


It's not that traps are necessarily "bad" and non-trap solutions are always "good".
(For example, compare a trapped 4BTV to a CHA-250B with "no lossy traps".)
Rather they are different methods of making an antenna cover multiple bands.  And,
as with many other aspects of ham radio, you have to consider your own needs,
limitations, and operating preferences in determining which best meets your needs. 
Most beams can be adjusted to optimize one parameter at a  particular frequency
at the expense of reasonable performance across the band (or, with things like element
spacing, over multiple bands.)

As Steve says, all antennas are compromises of some sort or another.  You have to
decide what trade-offs among the parameters best suite your operating preferences.

So rather than arguing whether traps are "lossy" or not (for which there is no single
answer because it depends on many factors), it makes more sense to discuss instead
factors such as F/B bandwidth, weight, wind loading, beamwidth, and the difference
between Front to Back or Front to Rear ratio as a measure of useful performance.
That would do more to shed light on choosing an appropriate antenna than arguing
over how misleading an advertising slogan is.


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 20, 2012, 03:35:56 PM
I agree that putting a smaller antenna up higher is a great idea! That is why Hex Beams are so popular. They are lightweight, and easy to stick up in the air, w/o heavy duty tower considerations.
But, wait a moment ?
I remember reading the best overall height for a triband beam antenna based in Newington, CT was only 52 feet!
I read this in QST
Do any of you guys remember that article ?


Title: RE: The Truth: How lossy are traps?
Post by: WB6BYU on December 20, 2012, 03:52:04 PM
Height above ground affects the take-off angle, and hence the coverage area.

If the ARRL analysis was looking at optimizing coverage to members in the
continental US, it would result in a lower height because so much of the ham
population is on the East side of the country, so would be reached by higher
angle signals.

Optimum height might be very different for DX in that case.


Title: RE: The Truth: How lossy are traps?
Post by: G3TXQ on December 21, 2012, 03:02:00 AM
Height above ground affects the take-off angle, and hence the coverage area.

If the ARRL analysis was looking at optimizing coverage to members in the
continental US, it would result in a lower height because so much of the ham
population is on the East side of the country, so would be reached by higher
angle signals.

Optimum height might be very different for DX in that case.

But the "optimum" height would be different for each of the three bands!

Steve G3TXQ


Title: RE: The Truth: How lossy are traps?
Post by: W6GX on December 21, 2012, 08:17:07 AM
Antenna designs are all about compromises.  Each design has it's own pros and cons.  I'd like to mention four positives on the trapless design.

1. The 'interactions' from an interlaced design could be positive (i.e. more positive gain).  The higher frequency elements act as directors on the low bands.  So just because there are 'interactions' it doesn't mean the 'interaction' is a compromise.  The positive interactive phenomenon is explained in the book 'Array of Light' by N6BT.
2. Trapless tribanders also work very well on the WARC bands.  The one I have experiences with has low SWR (less than 3:1) on 12 and 17, and moderate SWR (5:1) on 30.  It has some gain and a definite pattern, although the pattern is reversed (i.e. max gain is on the opposite side).  Running WARC bands on a trapped antenna is not advisable as the traps would self-destruct due to heat build-up.
3. Since there are no traps one could run legal limit power on all modes and all bands including the WARC bands.  This is a big advantage in a digital mode contest.  The same couldn't be said for most commercially available trapped designs (see my previous post on the power derating on high duty cycle modes)
4. Most trapless designs utilize a direct feed with no matching devices.  No matching devices means no loss, less mechanical complexity, and fewer maintenance issues.

73,
Jonathan W6GX


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 21, 2012, 10:34:36 AM
Antenna designs are all about compromises.  Each design has it's own pros and cons.  I'd like to mention four positives on the trapless design.

1. The 'interactions' from an interlaced design could be positive (i.e. more positive gain).  The higher frequency elements act as directors on the low bands.  So just because there are 'interactions' it doesn't mean the 'interaction' is a compromise.  The positive interactive phenomenon is explained in the book 'Array of Light' by N6BT.
2. Trapless tribanders also work very well on the WARC bands.  The one I have experiences with has low SWR (less than 3:1) on 12 and 17, and moderate SWR (5:1) on 30.  It has some gain and a definite pattern, although the pattern is reversed (i.e. max gain is on the opposite side).  Running WARC bands on a trapped antenna is not advisable as the traps would self-destruct due to heat build-up.
3. Since there are no traps one could run legal limit power on all modes and all bands including the WARC bands.  This is a big advantage in a digital mode contest.  The same couldn't be said for most commercially available trapped designs (see my previous post on the power derating on high duty cycle modes)
4. Most trapless designs utilize a direct feed with no matching devices.  No matching devices means no loss, less mechanical complexity, and fewer maintenance issues.

73,
Jonathan W6GX
LOL, and my Guy wires "act as reflectors and directors" for my Beam, but wait, there's more! I have a metal scarecrow (Obamacrow) on the very top of my antenna mast. And, the dimensions of this metal scarecrow was arrived at by computer simulation, to act as a director at multiple HF frequencies!~
You can read all about it, in my book, called "A Bunch Of Bullchit"


Title: RE: The Truth: How lossy are traps?
Post by: W7VO on December 21, 2012, 11:38:35 AM
I don't know what all the fuss is about. I use the power from my AL-1500 to melt the ice off my TH6DXX's traps, which radiates out through thermal conduction to the rest of the elements. Sure beats me climbing the tower to knock the ice off.  ;)

It is a win-win!

73 and Merry Christmas!

Mike, W7VO
Scappoose, OR


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 21, 2012, 02:36:38 PM
I don't know what all the fuss is about. I use the power from my AL-1500 to melt the ice off my TH6DXX's traps, which radiates out through thermal conduction to the rest of the elements. Sure beats me climbing the tower to knock the ice off.  ;)

It is a win-win!

73 and Merry Christmas!

Mike, W7VO
Scappoose, OR
Merry Christmas to you too Mike! No "fuss" really, just a bunch of bored old guys, talking about design compromises in our antennas.
As G3TXQ  correctly pointed out, trap, no trap, or full size trapless monobanders, ALL are a compromise, in one way or another.
I think it as all about finding the right compromise for YOU, and your operating habits.

I own the Hy Gain Explorer 14, with the 40 meter add on kit for instance Mike. I wanted a small (no more then 14 ft boom) tribander, with the best 10 meter performance I could buy, on that boom length. The Hy Gain Explorer 14 is almost a "monobander" on 10 meters, compared to any other tribander I could buy, on that boom length. It has dual driven elements on 10 (no traps) and a trapless, full size separate 10 meter reflector. Only the director element has a trap in it, for 10 meters.
W4RNL felt the dual driven element feed system used for 10 meters in the Explorer 14 (Hy Gain calls it a Para Sleeve) give a small amount of extra gain vs a single dipole feed.
It also gives great 10 meter bandwidth as well!
I think the Hy Gain Explorer 14 is overall the best 14 foot boom tribander money can buy, and certainly the best on 10 Meters. Like I said earlier, 10 meter performance is a MUST for me. I feel Roger Cox did an awesome job on the Explorer 14 design, and made the right compromises for me, and what I want and expect, from a small tribander.

I am up at 50 feet, pretty much the same height as my friends, one who has the 24 foot boom Hy Gain 10 meter monobander, and one who has the 4 element SteppIR.
WE are all within 20 miles of each other.

DO I kick their butts ? Heck no, the 24  foot boom computer optimized 10 meter Hy Gain 10 meter monobander is king, followed by the 4 element SteppIR, then my little Explorer 14.

But, I am "right in there" with the big boys. Both of my friends constantly comment on the clean pattern the little Explorer 14 has, on 10 meters.
I live near Tampa, and often have 1/2 of South America trying to bust into the back of my beam. Often, I can hear stations with less interference then they can, but I just can not match the firepower of the 24 foot 10 meter Hy Gain monobander.
The 4 element SteppIR does not have the firepower of the Hy Gain 10 meter monobander. The signal differences between him and me are not nearly as great as me and my Exporer 14 vs the Hy Gain 10 meter monobander.
So, I feel like I made the right choice, for me/

Now, interestingly enough, we have another Ham Friend who has a small Hex Beam.
He is only up at 38 feet (we are all at 50 feet) though. He has truly excellent rejection on his little Hex Beam.
In fact, this is his SECOND Hex Beam! He started out with a Traffie Hex Beam, and did very well with it too. But, he was less then thrilled with the lack of front to rear rejection, on 10 meters. I told him all about the KIO Hex Beams, and how Steve Hunt was able to get better rejection with his design. So, he took the Traffie Hex Beam to a Ham Radio Tailgate at the last Tampa Hamfest. It sold right away!
USED Hex Beams are nearly impossible to find here in Florida. WE have many retired Hams (winter only residents) who want a small, decent performing lightweight beam antenna, they do not have to worry about in every thunderstorm.
He was able to get 400.00 for the used Traffie Hex Beam, put a few hundred dollars more with it, and ordered the K4KIO Hex Beam.
I remember both antennas well, and the KIO Hex Beam did exactly what he expected, it greatly reduced the South American interference.

So, getting back to the thread, it is all about compromises. Like me, my Hex Beam owning friend found the right compromise for him.

Maybe because he is 12 feet lower in elevation then us, the signal from the KIO Hex Beam is nearly always from 1/2 to 1 S Unit lower then we are. I am sure the little 2 element Hex Beam just does not have the gain the 3 of us have, but it was the right compromise for him.
So many antenna makers IMHO seem to always push Gain as their reason for existence. IF I had told my Ham Friend that the KIO Hex Beam had more gain then his Traffie Hex Beam, I feel quite sure my friend would have kept the Traffie.
But, because Steve Hunt chose to offer better front to rear rejection in his KIO Hex Beam design, his design was chosen as a compromise my friend was willing to accept, and BUY!

The Force 12 owning ham in this thread bought the N6BT Force 12 design, because it does what HE wants it to do.

He appears to be as happy with his choice of antennas, as I am with my Hy Gain Explorer 14 semi trap design.

And, my other friend, with the 24 ft long Hy Gain 10 meter monobander, bought his Yagi, as the ONLY antenna on his tower! He sacrificed all the other HF Bands, to be "King Chit" on 10 meters.

Guess what, not surprisingly, it worked! It truly "messes with him" though, that he does not "kill us" with the big monobander.
But, never underestimate a determined Ham!
The last time we talked, he sent me to the M2 web page, to look at the 42 foot long M2 7 element 10 meter monobander  :'(















Title: RE: The Truth: How lossy are traps?
Post by: W6GX on December 21, 2012, 10:58:01 PM
And, my other friend, with the 24 ft long Hy Gain 10 meter monobander, bought his Yagi, as the ONLY antenna on his tower! He sacrificed all the other HF Bands, to be "King Chit" on 10 meters.

No offense to your friend's decision but why did he pick 10m and not 20m or 15m?  What does he do when 10m is closed?  If I could only have one band I'd have picked 20m.

But, I am "right in there" with the big boys.

The reason for this is because the law of diminishing returns.  Remember that most of the gain from a yagi comes from the first two elements.  When you add a third element and double the boom length you only add one additional db of gain.  Obviously three elements buy you more than just gain; it buys you a much better F/B ratio.

The last time we talked, he sent me to the M2 web page, to look at the 42 foot long M2 7 element 10 meter monobander

Tell your friend that instead of a M2 42' monobander he should get a long mast and stack two 24' boom monobanders on the same mast.  The stacked antennas will kick the M2's butt.

In summary, many folks often go overboard with large antennas and then realize the performance gain over small antennas is actually quite small.  Then they decide to get an even larger antenna.  The vicious cycle continues.

73,
Jonathan W6GX


Title: RE: The Truth: How lossy are traps?
Post by: KY6R on December 29, 2012, 08:45:16 AM
In my situation, stacking two 2 element yagi's (home brewed and designed using EZNec and also cross checked with YW, Yagi stress and even HFTA), and you will have what I show on my QRZ.COM page. I have the plots and the pictures there.

I chose 17M because I am 1 away from Honor Roll and wanted 6 dBd (+ if possible) on one band, and for the ones that I still need - and given that this cycle is as anemic as it is - 17M is the best band until we head down the cycle in a couple of years. (VOACAP used with all of the "rumors" that I know of as far as when certain entities that I need will be activated in the next year or so).

The stacking distance of my 17M monoband "2x2" is 1/4 wl - 54' for the top and 27' for the bottom.

No traps and the element spacing is optimized. I needed height and gain more than I needed F/B (look at the terrain map I have on my QRZ.COM page to see why I say this . . . .


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 29, 2012, 09:43:58 AM
In my situation, stacking two 2 element yagi's (home brewed and designed using EZNec and also cross checked with YW, Yagi stress and even HFTA), and you will have what I show on my QRZ.COM page. I have the plots and the pictures there.

I chose 17M because I am 1 away from Honor Roll and wanted 6 dBd (+ if possible) on one band, and for the ones that I still need - and given that this cycle is as anemic as it is - 17M is the best band until we head down the cycle in a couple of years. (VOACAP used with all of the "rumors" that I know of as far as when certain entities that I need will be activated in the next year or so).

The stacking distance of my 17M monoband "2x2" is 1/4 wl - 54' for the top and 27' for the bottom.

No traps and the element spacing is optimized. I needed height and gain more than I needed F/B (look at the terrain map I have on my QRZ.COM page to see why I say this . . . .
Wow, the bottom antenna is pretty low ? Would you not have been better off to use a single 4 or 5 element Yagi at 54 feet, vs the stack of 2's ?


Title: RE: The Truth: How lossy are traps?
Post by: KY6R on December 29, 2012, 01:24:46 PM
In my situation, stacking two 2 element yagi's (home brewed and designed using EZNec and also cross checked with YW, Yagi stress and even HFTA), and you will have what I show on my QRZ.COM page. I have the plots and the pictures there.

I chose 17M because I am 1 away from Honor Roll and wanted 6 dBd (+ if possible) on one band, and for the ones that I still need - and given that this cycle is as anemic as it is - 17M is the best band until we head down the cycle in a couple of years. (VOACAP used with all of the "rumors" that I know of as far as when certain entities that I need will be activated in the next year or so).

The stacking distance of my 17M monoband "2x2" is 1/4 wl - 54' for the top and 27' for the bottom.

No traps and the element spacing is optimized. I needed height and gain more than I needed F/B (look at the terrain map I have on my QRZ.COM page to see why I say this . . . .
Wow, the bottom antenna is pretty low ? Would you not have been better off to use a single 4 or 5 element Yagi at 54 feet, vs the stack of 2's ?


That's a great question. The AB-952 military mast is an absolutely incredible antenna "launching" system. It is way better than a push up mast, but not as good as a tri-legged tower. Anything large and top heavy - and you have to be careful how high you can go - for safety sake. I used to have an A3S up at 45' - and with a rotator, that was the limit.

I took the A3S down because it did what I wanted it to - but while I didn't worry about trap loss, I did worry about trap failure and the fact that all of those hose clamps would surely degrade and issues would pop up.

I found a C3S for $150, and that is going up as high as I can safely put it up - probably in the next couple of months.

The stack offers a way for me to get the higher antenna 55' up. There is no way in the world I can go that high with the C3S, even if I for go the rotator - which I will - to save on the "top heavy" factor.

I'm guesing the C3 will also go up at about 45', which is OK - but not as impressive as having this stack the way I have it now.

But that won't matter - because my "one solar cycle" goal of making DXCC Honor Roll will already be in the bag.


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 29, 2012, 04:08:41 PM
In my situation, stacking two 2 element yagi's (home brewed and designed using EZNec and also cross checked with YW, Yagi stress and even HFTA), and you will have what I show on my QRZ.COM page. I have the plots and the pictures there.

I chose 17M because I am 1 away from Honor Roll and wanted 6 dBd (+ if possible) on one band, and for the ones that I still need - and given that this cycle is as anemic as it is - 17M is the best band until we head down the cycle in a couple of years. (VOACAP used with all of the "rumors" that I know of as far as when certain entities that I need will be activated in the next year or so).

The stacking distance of my 17M monoband "2x2" is 1/4 wl - 54' for the top and 27' for the bottom.

No traps and the element spacing is optimized. I needed height and gain more than I needed F/B (look at the terrain map I have on my QRZ.COM page to see why I say this . . . .
Wow, the bottom antenna is pretty low ? Would you not have been better off to use a single 4 or 5 element Yagi at 54 feet, vs the stack of 2's ?


That's a great question. The AB-952 military mast is an absolutely incredible antenna "launching" system. It is way better than a push up mast, but not as good as a tri-legged tower. Anything large and top heavy - and you have to be careful how high you can go - for safety sake. I used to have an A3S up at 45' - and with a rotator, that was the limit.

I took the A3S down because it did what I wanted it to - but while I didn't worry about trap loss, I did worry about trap failure and the fact that all of those hose clamps would surely degrade and issues would pop up.

I found a C3S for $150, and that is going up as high as I can safely put it up - probably in the next couple of months.

The stack offers a way for me to get the higher antenna 55' up. There is no way in the world I can go that high with the C3S, even if I for go the rotator - which I will - to save on the "top heavy" factor.

I'm guesing the C3 will also go up at about 45', which is OK - but not as impressive as having this stack the way I have it now.

But that won't matter - because my "one solar cycle" goal of making DXCC Honor Roll will already be in the bag.
I understand now, we all do the best we can, with what we have.

Have you ever considered a Spider Beam ? They have no traps, and I have heard them, opening and closing bands, as well as being quite competitive in the pileups.
They weigh virtually nothing, is why I mentioned them.

I own a Aluma Tower T 50. It is self supporting for 10 sq ft windload in an 80 mph wind/ Currently, I have a Hy Gain Explorer 14, with 40 meter add on kit.
It is an outstanding antenna, for it's size.
But when I upgrade, I am 90 percent sure it will be to a Spider Beam.
My Hy Explorer 14 with the 40 meter add on kit, is 8.5 sq ft of windload, kind of close to the limits of my tower.
The Spider Beam is under 4 sq ft of windload, though it is much larger in boom length.
I can really upgrade my signal, gain the WARC Bands, and cut my windload in 1/2, by going to the Spider Beam!



Title: RE: The Truth: How lossy are traps?
Post by: KY6R on December 29, 2012, 07:26:05 PM
Have you ever considered a Spider Beam ?

I've actually built nested Moxon's - which are really great wire beams, and one for 20 and 15 might be what I go for as we start going down the cycle in a couple of years. I could keep something like that up 55'.

I especially like the Optibeam Wire Beam, but its way too expensive.

Lots of options - and I love designing and building my own antennas - never a dull moment here.


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 29, 2012, 08:45:20 PM
Have you ever considered a Spider Beam ?

I've actually built nested Moxon's - which are really great wire beams, and one for 20 and 15 might be what I go for as we start going down the cycle in a couple of years. I could keep something like that up 55'.

I especially like the Optibeam Wire Beam, but its way too expensive.

Lots of options - and I love designing and building my own antennas - never a dull moment here.
I Hear You, loud and clear Brother!
In fact, designing and building our own antennas are about all a Ham can do to improve our situations. I certainly lack the technical capacity to build a better transceiver then I can buy. I guess building a monster amplifier could be done, if one we so inclined, but that would not be me, and still does not address the receive gain possible with a gain antenna.

Man, I can clearly remember giving life to my very first Yagi. It was for 10 meters, and had 3 fairly wide spaced elements (.2 wavelength). I spaced elements equally wide apart on the boom, and cut the elements 5% longer for the reflector, and 5% shorter for the director. I "cheated" a bit, and ordered a Gamma Match from Kirk Electronics in Ohio, owned by W8FYR.
Tom Baker (SK) W8MMM, turned me on to Dr Aaron Self (W8FYR), and Kirk Electronics. They made and sold a lot of neat stuff, including Cubical Quad stuff.

I will never ever forget loading up my Drake TR 4 and calling CQ on my home made 10 meter monobander. I lived up in Detroit at the time, and the antenna was on a chimney mount of a 2 story home. The band was wide open, so I swung the little beam NE, and called CQ. To my great surprise, I soon had several Europeans coming back to me! I was sooo excited!
There was no computer modeling back then, there was the ARRL Handbook. It clearly said "experience has shown that these element lengths and spacings will work" and guess what ? They did!
I suppose I "got lucky", because my very first home made Yagi, had pretty darn good front to back as well! Because of the relatively wide spacing I used (.2 wavelength), it also had pretty good bandwidth!
My home brew 10 meter monobander could beat the Mosley 3 element tribander of one friend, and it also just destroyed my other friends Hy Gain TH 2.
Man, I was BIT by the home brew antenna thing! Then, a guy named Jim Lawson W2PV had the famous Papa Victor Yagi design, and I got hold of the National Bureau Of Standards Yagi Design sheet. I dreamed all winter long of what I would build, next!

So, here I am, nearly 30 years later, STILL into antennas, LOL

Right now, I have a Hy Gain Explorer 14, but my next project will probably be the spider beam.

Yes, the wire Opti Beam looks awesome too, of course.

One thing I noted from what you said about your top antenna in the stack "being at 55 feet" is this. I think that the effective height of a stack is determined by BOTH antennas. The radiation is from the middle of the stack I think ?
So, you are not really "up at 55 feet" if what I have been told is true.

I am quite familiar with the Force 12 antenna you speak about.
 It does not have the WARC Bands, but because it has no traps, it is said you can work them, w/o fear of popping a trap, and even has a bit of gain on 12 and 17!

I hear them on 17 all the time, being used with a tuner.

I do not think the Force 12 C 3 will equal one of your 2 element 17 meter monobanders, much less 2 of them in a stack.

But as far as a being your only HF Band antenna, it could turn out to be a winner for you, vs the old Cush Craft A 3.

Unlike the old A3, you can run it on 17 with power, and it may provide you enough antenna on 17 for those DXCC contacts you need:)












Title: RE: The Truth: How lossy are traps?
Post by: KY6R on December 30, 2012, 05:22:44 AM
One thing I noted from what you said about your top antenna in the stack "being at 55 feet" is this. I think that the effective height of a stack is determined by BOTH antennas. The radiation is from the middle of the stack I think ?
So, you are not really "up at 55 feet" if what I have been told is true.

I use an Array Solutions Stackmatch switch to be able to switch one, the other or both. I read Array of Light by Tom, N6BT, and in that book he says that the effective height of both is about 90% of the top yagi. So this means 50'.

My goal this past year was to get closer to Honor Roll - and I have worked and confirmed 6 ATNO's - all very rare - either requiring better antennas or that had massive pileups to bust through. I also used HFTA to give me a better clue what would "get me over the hump", and it surely has.

Now I'm only 1 away from Honor Roll - and as soon as I make it - the C3 will replace the stack. It seems like an odd way to go - but the stack with both switched in has between 6 - 6 dBd, and is at a height that gets me up and out of the "bowl" that I live in.

Great QTH for cycling - not so good for DX-ing, but I'm slogging along and trying to think and build myself out of this ditch  ;D



Title: RE: The Truth: How lossy are traps?
Post by: KE2TR on December 31, 2012, 07:44:05 AM
One reason the C3 work's so well is the design uses forward stacking, in the KA7NIQ's post on the three Hy Gain 3 el stacked monobanders you are looking at a short boom design plus I would bet that the stacking distance was at 10ft between beam's or less, well in that array you will see interaction and detuning of each beam. The old 10ft spacing between monobanders is BS, you have to see from what I have seen more like 15-20ft then you start to see the monobander's perform. Why do you see the top contest stations use spacing of much more than 10ft, because of interaction and pattern fluffing going on. I have seen this in real world results when I built and design my smallish contesting antenna farm back in the 90ies myself.
When the 3 bay stack of monobander's replaced the TH6 well the amount of interaction was detunning these beam's enough were the tribander even with its loss did better. But you take a C3 and you have three monoband antennas on one boom forward stacked were the interaction and detunning is modeled out then tested and modeled for best performance. Now a 2 element yagi doesn't have great FB but when tuned for max gain with much less loss than a traped tribander plus its light so you can stick it up on a taller mast you have a combo for very good results.
As far as the 4 element Stepper, that's a 34ft boom, great for 20 but that's extream spacing on 10&15, sorry I don't buy there gain figures for those bands but 20 I do. There 3 element beam is on a 16ft boom were 20m is close and 10&15 are perfect so you give up some gain on 20 but the higher band's are just right.
I am not saying that the Mosley,HyGain,KLM tribanders are bad, its that all of there traped designs have loss, these companies expect you to belive they will have monoband spec's, sorry to say they don't but to get a 10/15&20 stack of monobanders to perform you gotta have some space between these beam's so the tribander's do have an advantage were you don't need a huge tower for your install. The Force 12/ Optibeam tribander's are designed for max gain plus the least amount of interaction, they are a much easier install and will give the best performance on each band so if you want the top tier that's the way to go.


Title: RE: The Truth: How lossy are traps?
Post by: KA7NIQ on December 31, 2012, 08:24:32 AM
The Force 12/ Optibeam tribander's are designed for max gain plus the least amount of interaction, they are a much easier install and will give the best performance on each band so if you want the top tier that's the way to go.
OK, consider this, I am Mosley or Hy Gain. I have an antenna range, and I buy the Force 12 or Optibeam Designs, and measure them. I see they are "better", so what do I do ?
Allow a competitor to make a better antenna, or change my design ?
It is MUCH easier to make a NON Trapped antenna, less labor intensive.
Or, do you think that only N6BT and The German Optibeam designer are capable of designing a Yagi with forward stagger ?

When HY  Gain was in Lincoln Nebraska, I know for a fact they bought and tested competitive designs.
I imagine Mosley does the same.
WHY have they not changed to the "better designs", of the Force 12 and Optibeams ?
Unless, of course, they are not really better, after all is said and done ?