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Author Topic: The Truth: How lossy are traps?  (Read 37774 times)
KE2TR
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« Reply #30 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.
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KA7NIQ
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« Reply #31 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.











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WB6BYU
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« Reply #32 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.
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AA4PB
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« Reply #33 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.
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KA7NIQ
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« Reply #34 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.



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W6GX
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« Reply #35 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
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NH7O
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« Reply #36 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.
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KA7NIQ
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« Reply #37 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 ?
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KA7NIQ
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« Reply #38 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 ?


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WB6BYU
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« Reply #39 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.
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KA7NIQ
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« Reply #40 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.
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W6GX
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« Reply #41 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
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KA7NIQ
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« Reply #42 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" !











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KA7NIQ
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« Reply #43 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.









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W6GX
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« Reply #44 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
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