I understand the concept of a travelling-wave antenna, and I'm not
casting aspersions. I'm just suggesting that you should think about
doing some tests with a field strength meter comparing this antenna with
some kind of reference antenna. Like maybe scaling it down to where the
maximum wavelength is 10m, or even shorter, and comparing the output
with a resonant groundplane or vertical dipole.
On 8/25/2015 1:34 PM, Bill Crowell wrote:
Yes, most folks look at the terminating resistor and immediately think
of a dummy load.
What most fail to realize is the total amount of loss of tuners and coax.
The rule is that matching impedances causes the most power transfer to
occur. There was an excellent article in QST showing the different
antenna/tuner configurations and the amount of loss. Most of the time
much greater than loss in this system.
Thanks for taking the time to read up on it. All antennas are a
compromise.
73!
Bill Crowell
Pearland, TX
From: BVARC <[email protected] <mailto:[email protected]>>
on behalf of Jonathan Guthrie via BVARC <[email protected]
<mailto:[email protected]>>
Reply-To: BRAZOS VALLEY AMATEUR RADIO CLUB <[email protected]
<mailto:[email protected]>>
Date: Tuesday, August 25, 2015 at 1:30 PM
To: BRAZOS VALLEY AMATEUR RADIO CLUB <[email protected]
<mailto:[email protected]>>
Cc: Jonathan Guthrie <[email protected] <mailto:[email protected]>>
Subject: Re: [BVARC] TTFD Antennas - N4HPG
I would be concerned that the terminating resistor would be consuming
most of the power on the lower frequencies.
The article talks about the small amount change in SWR over a 5:1
frequency range, but SWR by itself tells you nothing about an
antenna's performance, and the article says that the power lost to the
terminator is an open question.
On 8/25/2015 10:50 AM, Bill Crowell via BVARC wrote:
Howdy All,
I was listening to the net last night and John, K5IZO, was
encouraging folks to get on 75m. Yay!
I’ve been working on a project for a number of months. Some of you
know that I use a TTFD antenna. TTFD or T2FD. It stands for Tilted
Terminated Folded Dipole. This antenna is not widely known because
it’s not featured in any ARRL publications – at least since 1949.
There are some good reference sources such as the RSGB wire antenna
book. There are also some detractors that don’t understand the theory
of operation.
Here’s a link to the original article:
http://www.scribd.com/doc/42625655/An-Experimental-All-Band-Nondirectional-Transmitting-Antenna-T2FD
You’ll notice that the antenna is a 600-ohm design. It is a balanced
antenna.
Perhaps Rick Hiller and I should give a presentation on it.
I’ve been using the B&W version for a number of years, but want to
run higher power. That means a better matching transformer for 50:600
ohms and also a more robust terminating resistor. The antenna works
well from 75 to 10m with 1.5:1 SWR or better on all bands. This is
because it’s a traveling wave antenna. Mismatch is soaked up by the
terminating resistor. No tuner is needed. The antenna works from the
lowest frequency up. That means a 80m antenna works on all bands from
80-10m. A shorter antenna works from 40-10m. B&W says 6m, but I’ve
not tested my high-power balun for 6m yet. I never promise what I
haven’t tested.
I’m hoping to bring a completed unit of the high-power design to the
club meeting on 9/10 so y’all can look at it. I should probably fire
up N4HPG.com website and post some pictures.
_If you can have only 1 antenna, this is the one to have. I like to
hunt DX and change bands without having to tune. Get as long an
antenna as possible!_
------------------------------------------------------------------------
The folks at B&W now want $825 for their version. That’s insane! But
they sell mostly to military and governments.
I’m making one antenna for myself that will be all my build. I’m also
making a heavy-duty one for N5XZ. Being gainfully unemployed and
having a workshop, I’m testing the waters to see if others might want
one.
When we put up an antenna, the neighbors usually notice. I’m making
my version with 14awg white MTW wire and clear, acrylic spacers for
the antenna and the ladder line. The balun box mounts on the wall and
transforms the 50 ohm unbalanced to 600 ohm balanced. It’s a 6x6x4
box because there are 4 toroids.
Based upon present materials, I believe I can produce the standard
antenna – 1kW for normal operation for $349. I’m still working on the
N5XZ 1.5kW RTTY Contesting version that will be a bit more.
If you want to build your own, feel free to steal my design!
For those who would like a built and tested unit, let me know. I’m
trying to decide if I should get into the antenna business.
73!
N4HPG
Bill Crowell
Pearland, TX
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Jonathan Guthrie KA8KPN
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