In a message dated 96-07-03 06:31:42 EDT, you write:
>I need some technical enlightenment. Why are these losses so high? What's
>the relationship between input resistance and losses? What, if anything,
>does this suggest about the possible losses in tribander traps? Has anyone
>actually put tribander traps in a test rig and measured the losses? I'd
>sure like to stop conjecturing about the losses and see some empirical data.
>I seem to remember that people used to measure the losses in coax at vhf by
>running a meaured amount of power into a piece of coax submerged in a
liquid, and >measuring the heat rise. Couldn't the same be done with traps,
particularly with high >enough power so that the heat rise would be large
relative to ambient?
>
Pete --
I'm not an engineer but have much experience in the realm of antennas.
From anecdotal experience from working on and installing antennas at over
100 amateur stations here in the Pacific NW, being the National Sales Manager
for Hy-Gain and reading/talking to antenna designer/gurus such as McCoy,
Lewallen, Schiller, Straw, Breakall, etc., I feel that I have an informed
perspective.
That said, one of the problem with trapped antennas (and traps) is
simply the number of connections involved. Each connection has ohmic loss
and trapped antennas have many more connections and cummulative ohmic loss.
Second, a typical coil in open air has a Q in the range of 300-400. Put a
metal cap on it (like all the manufacturers do) and the Q drops significantly
to the 150-200 range. I think the inference here is that it is less
efficient as the Q drops. Next, there is some current unpublished research
that is taking place on trapped antennas. Instead of having a nice
sinusoidal curve like the one that surrounds a dipole or monoband yagi
element, the sine wave around a trapped element is truncated with apparently
little actual radiation taking place past the traps. These are the reasons
why I made the statement that the new trapless multiband antenna designs are
lowering the lid on the coffin of trapped antennas. I'm sure that these
aren't the only issues.
I also would like someone to take your challenge and run some credible
tests once and for all. 73, Steve K7LXC
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