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Author Topic: Tilted Terminated Folded Dipole (T2FD) for QRP  (Read 4429 times)
WB4WZR
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Posts: 17




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« on: November 20, 2007, 12:24:26 PM »


This sounds like a great antenna for portable QRP.  At 7 MHz the 17 inch spreaders are a bit of a problem, but its 47 ft length might help getting it up among the trees.

Does anyone have any experience with it?
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W3JJH
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« Reply #1 on: November 20, 2007, 02:17:22 PM »

The energy spent heating the terminating resistor is not radiated as RF.  While a T2FD antenna is somewhat more efficient than a dummy load, it is more complex than a simple doublet fed with ladder line and a tuner.

A simple vertical antenna made from a 33 ft long wire taped to the side of a nonconductive pole or mast operated with three or four 33 ft radial wires on the ground would give much better 40 m performance than a T2FD in less space.

You can learn more about the T2FD at <http://www.cebik.com/wire/t2fd.html>.
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W8ZNX
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« Reply #2 on: November 20, 2007, 03:15:36 PM »

save your money
single 1/4 wave wire in a tree
with a single 1/4 wave counter pose
underneath it on the gound
hooked to a hb tuner
will run rings around the T2FD

dit dit mac

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W5ESE
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« Reply #3 on: November 21, 2007, 12:02:29 PM »

I agree with the previous two posters.

An article in QST about NVIS techniques mentioned
that the poor performance of the TTFD antennas was
one of the "lessons learned" from Hurricane
Katrina. The volunteers obtained MUCH better
results on 80 and 40 meters with full length
coax-fed fan dipoles.

If you are an ARRL member, you can read the article
for yourself at:

http://www.arrl.org/files/qst/qst-binaries/Straw1205.pdf

My personal favorite "cheap and effective" portable
antenna is the center fed zepp using TV twinlead
or 450 ohm window line as the transmission line.

73
Scott
W5ESE

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WB4WZR
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Posts: 17




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« Reply #4 on: November 21, 2007, 04:19:13 PM »



Thanks to all for the comments on the T2FD.  I won't be building one.
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NXET
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Posts: 1




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« Reply #5 on: December 02, 2007, 08:04:46 PM »

Well hold on here a min folks.

Before you get all the wana-bee's that read a lot and know little about the real antenna you might want to talk to some who have used them and found them to reallly work great.

Now while some have used them off octive resonance... if they are in resonance you don't put much power into the matching resistor and it is a good antenna then.   I have found that they actually work much better than the standard dipole or verticle.

What you have to weight out is the octive resonance frequency.

If your on a node then they radiate out well... with little or no power going to the matching resistor... off node and your sending all the power into the matching resistor and not much is radiated.  This is true.

Now one other point that most of these so called experts fail to tell you is that the matching of the Zep or dipole off resonance (insertion loss of the tuner/matching device) will almost be as much as the loss off node into the folded dipoles matching resistor.  So which is the truth?   When you do the math you will find that they are not as bad a antenna as they would have you believe (mainly because they never used one but become a expert off the advise of others)

The benifit of using one also then does not require one to haul around a matching device.  Simple and yet effective.

A good antenna .. if you stay on frequency of the nodes... which are space and lenght dependent.

Not so good a antenna for ease of installation due to the spreaders and twisting.  

Each have their own faults and benifits.  Best to go experiment and find out which one you like/works best for you  and quit listening to these "experts" who haven't

73"s
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W3JJH
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« Reply #6 on: December 05, 2007, 07:23:56 PM »

Sam:

I'm not a wannabe.  I've both done the math and used a T2FD antenna.  Both the math and the real-world performance agree that the losses in the terminating resistor are normally in the 50 % to 90 % range.  Even at the narrow sweet spots, the losses exceed 25 %.  Using an antenna with a built-in attenuator is a dumb idea for a QRP operator.

Loops and folded dipoles are good antennas.  Antennas with terminating resistors may be useful for receiving, but using a transmitting antenna with a built-in attenuator is a dumb idea for a QRP operator.

73 de W3JJH
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NJ2E
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Posts: 35




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« Reply #7 on: December 31, 2007, 08:03:25 AM »

I would suggest you go to the L. B. Cebik, W4RNL web site for a full evaluation of the the T2FD (Vertical/Sloping and Horizontal). In fact if I am looking at a particular antenna or concept this is my first research stop. Happy New Year and 73s to all. Don NJ2E

http://www.cebik.com/wire/t2fd.html

http://www.cebik.com/wire/wbfd.html

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WB6CSH
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Posts: 2




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« Reply #8 on: October 10, 2014, 12:25:10 PM »

The tilted terminated folded dipole (TTFD or T2FD) has been a useful antenna, despite the opinions to the contrary. Marine operators use the TTFD routinely since it can be used over a wide swath of frequencies without an ATU.

The ATU cannot perform miracles, and may NOT provide a good match for the many frequencies used in marine work. An ATU introduces losses into an antenna system, too! Marine frequencies are NOT the multiples of a fundamental frequency that the amateur bands enjoy. Marine frequencies are in the spectrum between 2 MHz to 25 MHz.

Most hams have never tried a TTFD, and are offering an opinion based on someone else's opinion. I tend to agree that using a TTFD with a 40 meter single-band QRP transmitter doesn't make sense. Why not use a half-wave center-fed horizontal (or sloper) or a quarter-wave vertical with appropriate counterpoise? Even an end-fed ZEPP would provide better results and be MUCH SIMPLER to construct than a TTFD!

Oh, and to the previous comment:
"My personal favorite "cheap and effective" portable antenna is the  CENTER FED ZEPP using TV twinlead or 450 ohm window line as the transmission line."

 All I can say is that by definition a ZEPP is ALWAYS an end-fed antenna! Goes to show you how much some hams know about antennas!

I'm just saying....  Roll Eyes
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AA4PB
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Posts: 12899




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« Reply #9 on: October 10, 2014, 01:10:35 PM »

The T2FD has been used by military and commercial stations because they can operate on multiple frequencies without tuning. Trading off efficiency for broad-band operation is fine for those users because they aren't operating at QRP power levels. The T2FD is a very poor choice for a QRP operator using it in the ham bands.

Yes, I've owned one and I've run tests with it for a government agency. The lower in frequency you go (i.e. 80M and 40M), the more power is dissipated as heat in the resistor and the less power that gets radiated.
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WB6BYU
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Posts: 13341




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« Reply #10 on: October 10, 2014, 01:27:49 PM »

The T2FD (and wide-band resistive-loaded folded dipoles in general) have been extensively used, modeled, and analyzed
by W4RNL and others.  There really isn't a lot of mystery left about them, though there is a bit of variation depending
on the specific balun, termination resistor, wire spacing, etc.


The efficiency varies up and down in cycles across the operating range.  On average, such an antenna is about 5 to 6dB
down from a straight center-fed wire of the same length on those frequencies where the antenna is longer than about
1/3 wavelength.  On some frequencies it is worse, and sometimes it is better, but I don't remember that it was ever down
less than 2 or 3 dB.  The losses increase fairly quickly as the antenna is made shorter than that, which would include the 47'
antenna used on 40m, or the 95' version used on 80m.

For many users, especially those who wave to cover multiple frequencies and have power to spare, that isn't a problem.
The military, National Guard, Civil Air Patrol, and other groups use a lot of them - they don't need any tuning, and they
will work any frequency in the range that you happen to need.  That's great when you don't have a skilled radio technician
available to set it up.


I remember reading an article in 73 or CQ about a QRP operator using one because the low SWR decreased the losses
in his coax.  Unfortunately, the losses in the antenna (even with an optimum length, which was NOT mentioned in that
article) were greater than what he was saving with any reasonable coax-fed antenna.

So let's look at the issue of tuner losses.  True, all tuners have some loss, and there are some poorly-designed QRP
tuners that are particularly bad.  But if tuners in general really were as lossy as many seem to think then they would
melt a lot more often at higher power levels.  I've seen what happens trying to match a radical impedance on 160m -
the coil supports melted and the coil got so hot it unsoldered itself at 100W (which was well within the tuner rating) -
that's what a > 3dB loss in a tuner can do, because all that lost power has to be dissipated as heat.  But if the coil
in your tuner isn't getting hot to the touch after a long QSO at 100W, then your tuner losses can't be all that bad.
When used with a reasonable load impedance the losses can be insignificant.  You can see for yourself:  try
W9CF's tuner simulator applet here:  http://fermi.la.asu.edu/w9cf/tuner/tuner.html
Set it to match a 1000 ohm load on 40m (SWR = 20 : 1) and see how lossy it is.  

In most cases the tuner introduces less loss than a T2FD - especially one that is less than 1/2 wave long.

(You can also optimize the tuner design for the impedances likely to be encountered with a particular antenna, but
most folks don't bother.)


So, yes, there are situations where the convenience of multi-band operation at low SWR is more important than
signal strength.  And those of use who operate QRP know that, when used with a 100W radio, it still radiates more
power (on most bands) than our 3W and 5W radios feeding a dipole, so of course it can make plenty of contacts.
In many cases the losses are less than 1 S-unit, and won't make a lot of difference when signals are strong.  But
when you are struggling to get your signal through the noise you may appreciate a better antenna.

It all comes down to trade-offs.  I have a couple of resistive-loaded antennas (100 ohms across the coax with
a random length of wire tied to it) for times when I have more transmitter power than needed and I don't
want to bother with tuning an antenna.  But for packing a QRP rig in the field, where battery capacity limits the
power I can reasonably run, my preference is not to waste half to 3/4 of my power in an inefficient antenna.
I can string up a dipole using 50' of RG-174 on 10m and still have less loss than the best case of a T2FD.
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NK7Z
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Posts: 823


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« Reply #11 on: October 10, 2014, 08:42:41 PM »


This sounds like a great antenna for portable QRP.  At 7 MHz the 17 inch spreaders are a bit of a problem, but its 47 ft length might help getting it up among the trees.

Does anyone have any experience with it?
Much loss in this type of antenna...  It's forte is it needs no tuning of any kind, from 1.5 to 30 MHz., and is flat at around 1.5 to 2 to 1 SWR across that entire segment of the HF spectrum.  The military loves it for ALE...  Think Dummy Load with wire hanging off of it...  I use mine for MARS work, for out of Ham Band transmissions...  Works well for that, but for a QRP, I would not touch it, the basic design wastes power by intent.
« Last Edit: October 10, 2014, 09:22:35 PM by NK7Z » Logged

Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
VK3YE
Member

Posts: 26




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« Reply #12 on: October 11, 2014, 10:32:38 PM »

What the others said.  Non-amateur users typically need HF only for a single hop and may have 20 - 100w to play with.  There's enough margin there on middle HF frequencies to provide the desired communications despite the antenna loss. 

The performance of what I call the 'resistor family' of antennas (like the T2FD) with QRP is like this: https://www.youtube.com/watch?v=46coth1Z9rQ

Yes you may get contacts but it will be a struggle when other antennas will be so much better in the available space.
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N9AOP
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Posts: 149




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« Reply #13 on: October 13, 2014, 03:14:10 PM »

The T2FD antenna definitely has its place but not for QRP unless at the higher frequencies.  It is a great QRO antenna and works great for ALE.  As with any other antenna, it depends on how it is mounted.  In the beginning I read a lot of opinions from hams that said that it was just a big dummy load.  I think they parrot what they have heard because after about 6 months of trying different configurations I found that it works well for stateside and also DX contacts.  Not as good as a pro96 but not bad either.
Art
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