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Author Topic: T2FD  (Read 14429 times)
W7LPN
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Posts: 9




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« on: May 15, 2010, 10:57:20 PM »

http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fd.html

http://www.buxcomm.com/catalog/index.php?main_page=product_info&products_id=2220

Looking for first hand user, real life experience with the T2FD. Not from a competitor, not from an engineer or antenna modeler who has never used, built, or bought one. there is one anonymous e-mail response below regarding a QRZ forum thread which turned very negative without any first hand experience. They only quoted sources or made fun of advertisers claims.


Rick W7LPN, thanks for your Emails: re: T2FD

"Trust me, I've read them all.... Even ole Marty J.  notes of distain:...
The problem now is, all the advertisers who pay big buck$ with (Ham Magazines- names removed) to advertise their Antenna tuners have now threatened them to redraw or reduce their advertising if they continue to publish articles about T2FD, and WINDOM (tunerless) antennas.  ANY Antenna that does not use an antenna tuner that could be written about in these pubs are bad news for the leading Amateur Publications.  Cebik is now SK, but back when he wrote that piece, he was writing books for QST/ARRL.
For eighteen years, I was the digital editor of XX magazine, never missed a month writing my column.. sometimes several...  Then when I wrote an article about the T2FD, they refused to print it... then I wrote an article about the Windom.... suddenly I had some sort of writers disease... they would not print it either.
I was furious, as I had put a lot of time and effort into those articles (column).  
I gave them my "notice" and immediately stopped writing for them.  They got P/O'd and then one of the employees of XXmag (nameless), called and informed me WHY they would not print my articles about the antennas that did not need an Antenna Tuner....
Seems two of their biggest advertisers threatened to pull all their advertising dollars if they ever gave credence to any article(s) that took away antenna tuner sales.
It's a sad day when politics enters our hobby, and begin to dictate editorial policy… and the rank-n-file HAM suffers because of the all-mighty dollar.
Up until 1995, all the handbooks, HAM magazines, and league publications (Antenna Books) had articles about T2FD, Windoms and specific antennas that did not require an antenna tuner.  
SUDDENLY, all the Antenna handbooks, Annual Amateur Radio Handbooks.. and publications sold by the OOOO, XXX, or UU, took a noticeable difference in their hobby antenna related content and antenna information:!
ALL, I mean ALL reference to the T2FD, the Windom, and tunerLESS antennas was noticeably missing from these rags! Here be side me, in my BOOK CASE are the last 4 years of ARRL Annual Handbooks.  Not a word about these antennas.
Add to that, I have the ARRL Classic Wire type Antenna Handbook; first Edition Copyright 1999 through 2009.
Here is a book that should be bulging with T2FD, Windom and other WIRE type antennas (that don’t need antenna tuners), alas… NOTHING!
I tried to make a big noise, but I was laughed at because I related this to some of the "powers-that-be" at the league, and CQ.... they poo poo'd it and denied it no less.
I rest my case.
Now you understand why I don't advertise in any of these “Hobby Rags.”
Every chance they get, they'll have some of their cronies put something on XXXXX(on-line forum) in print, trying to discredit me.  I'm still here, and most of them are out to pasture.
AND now’ you know "The rest of the story !"
Have a great weekend."
73  anonymous

« Last Edit: May 15, 2010, 11:01:23 PM by Rick Frazier » Logged
N3OX
Member

Posts: 8916


WWW

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« Reply #1 on: May 15, 2010, 11:43:49 PM »

Quote
Looking for first hand user, real life experience with the T2FD. Not from a competitor, not from an engineer or antenna modeler who has never used, built, or bought one.

Why?  Isn't your mind already basically made up?  Do you want someone to tell you the resistor isn't going to dissipate significant power on some bands?   That is what it's there for.  It's a loss network to broaden the SWR bandwidth at the expense of some signal.   Various sources, models included, can tell you the percentage efficiency of the antenna on each band you want to use it on.   Only you can decide whether the convenience is worth the loss. 

If you believe your ranty, persecuted friend here, and think that the only reason hams don't use T2FD antennas all the time is because tuner manufacturers have hoodwinked us, why don't you just buy or build one and find out how it works?

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KH6AQ
Member

Posts: 7718




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« Reply #2 on: May 16, 2010, 12:43:54 AM »

That is a short Wideband Terminated Dipole. Yes I have built, modeled, and written about this type of antenna. The Buxcomm specified gain is at 28 MHz. These antennas are simple to model with NEC-2:

T2FD radiation efficiency:
80 meters:  4%
40 meters: 16%
20 meters: 25%
15 meters: 35%
10 meters: 55%
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K4SAV
Member

Posts: 2594




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« Reply #3 on: May 16, 2010, 07:37:43 AM »

Buxcomm makes six versions of this antenna, ranging from 33 ft to 85 ft.  Which one are you interested in?  Of the two references you gave, one was for a 33 ft version and the other was for an article on a 67 ft version.  There are other versions out there which are much longer. 

If you are interested in hearing from people that have used one, check the eham reviews.  You won't find any performance reports there, but you will find some opinions of how people like them.  I have also used the B&W T2FD, but there is no use giving you my satisfaction report because I'm sure it won't agree with yours.  I could also give you an analysis, and reference to other people's analysis, but you stated you weren't interested in that.

Jerry, K4SAV
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G3TXQ
Member

Posts: 1845




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« Reply #4 on: May 16, 2010, 02:37:16 PM »

SUDDENLY, all the Antenna handbooks, Annual Amateur Radio Handbooks.. and publications sold by the OOOO, XXX, or UU, took a noticeable difference in their hobby antenna related content and antenna information:!
ALL, I mean ALL reference to the T2FD, the Windom, and tunerLESS antennas was noticeably missing from these rags! Here be side me, in my BOOK CASE are the last 4 years of ARRL Annual Handbooks.  Not a word about these antennas.

Your anonymous eMail correspondent needs to check his facts. The latest (21st Edition) of the ARRL Antenna Book has plenty about the Windom and OCF dipoles - pages 7-6 to 7-9. QST magazine also seems happy to carry advertising for the TFD - March 2010 Barker & Williamson.

Steve G3TXQ
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WB6BYU
Member

Posts: 18237




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« Reply #5 on: May 17, 2010, 09:43:53 AM »

Terminated folded dipoles such as the B&W have been commonly used by the military and other
users who need wide-band coverage at relatively low SWR.  There is a trade-off in this case
between efficiency and wide SWR bandwidth.  If you have relatively unlimited power and/or a wide
range of frequencies to choose from, efficiency isn't as much of a problem.  If you have a limited
number of frequency bands available and are trying to communicate with low power, efficiency may
be critical to getting the message through.

The Oregon Office of Emergency Management includes an ARES/RACES station that had one of the
B&W dipoles up for several years.  They later replaced it with a different wide-band design with
better efficiency.  This was particularly a problem as the last sunspot cycle started fading - the
90' antennas are adequate on 40m, but as the critical frequency dropped and operations shifted
to 80 and 160m the performance was dismal.  Operators during Katrina noticed the same problem -
there were cases where they had to put up a conventional half wave dipole to maintain communications
where the terminated folded dipole wasn't up to the task.  I've seen similar results building them
for a VHF antenna range.

All of this is well correlated to the results of antenna modeling and the manufacturer's claims of
power handling capacity of the antennas:  you can measure the temperature rise in the terminating
resistor and calculate the power dissipated, hence the efficiency of the antenna.  Basically the
efficiency drops precipitously when the antenna length is less than about 1/3 wavelength.  So
the common 90' model isn't too bad down to 40m, but 80m is poor and 160m is abysmal, even though
the SWR is low.

For shortwave reception, however, efficiency isn't as important, because the signal to noise ratio
is set by the received noise instead of that generated by the receiver.  That's why you see the
T2FD used in the SWL community.


That's not to say that it might not be a good choice for someone who is more concerned
with SWR than with radiated power.  But an ordinary half wave dipole is cheaper, radiates more
power, and has a low SWR across the band (at least on 40m and up), which is why hams are
more likely to put up several dipoles on a common feedpoint rather than choosing the terminated
folded dipole.

The T2FD has been around for a long time - it was originally fed with 300 ohm twinlead and
installed as a sloper.  But it never has been very popular among hams because it doesn't
work very well for our sort of operation, in spite of the low SWR.


But, if you want conspiracy theories, consider the true fan dipole:  it is easily capable of
covering 7 to 30MHz at 2 : 1 or better throughout the range, using only a 4 : 1 balun with
5 wires on each side each 40' long, arranged in a fan.  Efficiency is high, cost is relatively
low, SWR is good, and it doesn't require any tuning (as multiple half wave dipoles on a
common feedpoint do.)  Such antennas have been available commercially for Military and
Commercial operations for decades, but I don't remember seeing any mention of it in a
ham magazine.
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WB2WIK
Member

Posts: 21833




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« Reply #6 on: May 17, 2010, 04:35:44 PM »

Terminated folded dipoles such as the B&W have been commonly used by the military and other
users who need wide-band coverage at relatively low SWR.  There is a trade-off in this case
between efficiency and wide SWR bandwidth. 

That's the crux of the matter.  Government agencies, embassies, etc. aren't using HF today nearly as much as they did 20-30-40-50 years ago, because a lot of this is all handled by satellites now.  They use HF as a "backup," unlike the old days when HF was primary.

Back when I was involved with Army MARS, T2FDs were in pretty common use (late 1960s) because the equipment ran tons of power and there was a lot of signal margin.  We used antennas that didn't require tuning, because many operators didn't know how to tune anything, they just knew how to pass traffic.

Amateurs should train themselves to know how to tune stuff, which negates the need for broadband, low-SWR antennas.  Especially when we're not running several kilowatts of power and don't have the signal margin.
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