Posted by
k6dgw on
Aug 14, 2017; 6:24pm
URL: http://elecraft.85.s1.nabble.com/Re-Elecraft-Digest-Vol-160-Issue-18-More-on-the-TTFD-tp7633382p7633391.html
True. For any given total length, the loss to the termination increases
as the TX frequency goes down, and the loss vs freq curve rises rapidly
near the lower end. The solution of course is to make the total length
of the FD, end-to-end long enough that the termination loss at the
chosen TX freq(s) is close to 3 dB. This works well for the military
and government installations who often have a small number of assigned
frequencies, and the ubiquitous "B&W Over Armories" version capitalizes
on this. ALE complicates that strategy somewhat of course.
As has been noted before, antenna choice is a basket full of trade-offs
and not every application for an antenna is to make Honor Roll in a
week. Paraphrasing Rowdy, my #1 while in the military, "We sometimes
find ourselves trying to pick fly poop out of the pepper." In that
vein, I suspect that 95%+ of the time, anything I can work with 10 W on
20 m from my K2 I can also work with 5 W on 20 m from the same K2. Of
course, 87.49% of people make up their own statistics too. [:-)
73,
Fred ("Skip") K6DGW
Sparks NV USA
Washoe County DM09dn
On 8/14/2017 8:54 AM, Joel Hallas wrote:
> The one point I disagree with is the
> statement that the terminating resistor dissipates half the power. The power
> dissipated is a function of frequency and, while it is not far from 3 dB at
> the high end of the frequency range, it absorbs much more at the low end --
> about 90%! Not only is that 10 dB less signal on transmit, but the resistor
> power rating needs to be 90% of the transmit output, if high duty-cycle
> modes are used. Note that it is not as big a problem on receive, since the
> receive S/N on the lower bands is sufficiently atmospheric noise limited,
> that the receive S/N is not greatly impacted, even though the s-meter will
> read lower by 10 dB.
>
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