On Sun, 14 Dec 2008 14:32:09 -0600, K4SAV wrote:
>Isolation coils is a term invented by the company. I think what they
>are doing is using a self resonant coil but not operating it at the self
>resonant frequency. This requires a little explanation.
>Looking at their coils, it is obvious that these are not high Q coils,
>yet they claim they will handle full legal power. It's not likely you
>can do that with low Q coils operating at their self resonant frequency
>in a trap dipole.
I have MEASURED the coils on two of Barry's antennas and put them in an NEC
model. They are NOT traps, they are not "isolation" coils, they are simply
loading coils. The significant results of the model are in the PPT that I
listed in my previous email. This design fooled me -- before I measured the
coils I also thought they were traps. They are not -- indeed, I never found
a resonance below about 15 MHz!
I'm not sure what you'd call "high Q," but I've used two different models of
Barry's antennas running legal power for lots of contesting (heavy duty
cycles, so lots of power stress) with no ill effects. After several years of
this, I can see no signs of heating, and their actual Q is higher than I can
measure with any accuracy.
The antennas I've used and tested are the long 80/40 and the long 160/80, to
which I've added a 40M fan element. One of my buddies has a multi-band
version that's pretty short. I helped him put it in his trees. It's not
nearly so well behaved, and I wouldn't recommend it.
73,
Jim Brown K9YC
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