On Sun, 22 May 2005 10:34:19 +1000, Bob Bob
wrote:

My first suggestion would be to use a terminated folded dipole cut large
enough for 80m and the rest would just work. Have a look at Mr Cebik's
website for details.

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

Good morning, Bob.

Wouldn't the terminated folded dipole be too lossy at the lowest
frequencies of interest?

In any case it looks like a terminated folded dipole would cost at
least a full "S" unit over a dipole, at any frequency (and much more
than that down by the low end of the design range).

However, looking through L.B.'s website gave me another idea ... what
about a triband full wave loop similar to what is shown in the
attached JPEG? There would be a single wire on the "fed" side of the
loop, tapped off at points along its length to create anchor points
for the other three sides of a loop for each frequency.

Have any of you tried anything like that, and how did it work?

CJ

C. J. Clegg wrote:
However, looking through L.B.'s website gave me another idea ... what
about a triband full wave loop similar to what is shown in the
attached JPEG?

Have any of you tried anything like that, and how did it work?

Unlike dipoles, there would be heavy interaction between the
loops on 40m. The feedpoint impedance of an 80m dipole is
very high on 40m and most of the power goes into the 40m
dipole. The feedpoint impedance of an 80m loop is low on
40m so the power is shared with sometimes unexpected results.
You can probably model it with the free demo version of EZNEC
available at www.eznec.com
--
73, Cecil http://www.qsl.net/w5dxp


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I'll admit that I havent played with the TFD but would agree that the
resistive termination would introduce a 3dB power loss. One has to ask
though whether that will be a problem at 80m given band noise etc.

To tell you the truth if I was trying for a 3.5, 4.5 and 7Mhz antenna
I'd probably use just two (crossed) dipoles and figure a way to
mechanically tune between the lower frequencies. Even lumped C comes to
mind.

Only HF loop I ever played with was a 40m NVIS..

Cheers Bob VK2YQA

C. J. Clegg wrote:
---
Wouldn't the terminated folded dipole be too lossy at the lowest
frequencies of interest?

Have any of you tried anything like that, and how did it work?