On Sat, 12 Aug 2006 23:32:09 GMT, Cecil Moore wrote:

Walter Maxwell wrote:
IMO, Cecil, you've been hoaxed if you thought a coil self-resonant at 6.6 MHz
was a high-Q coil at 4 MHz.

All I know is that Texas Bugcatcher coils tend to be
near the top of the the 75m mobile shootout results.
Using base loading on a GMC pickup, it is resonant on
3.8 MHz with a six foot stinger. Remove the stinger and
it is self-resonant at 6.6 MHz.

My 75m Texas Bugcatcher coil was a gift from K7JEB.
It is 26.5 turns at 4 tpi on a 6" air core form.
Calculates out to be about 70 uH. I don't know how
to make it higher Q.

I'm guessing #12 wire in the coil, which leaves lots of spacing between turns ,
which should make the distributed capacitance very small. I haven't made any
calculations, but a seat of the pants estimate would say the self-resonant
frequency would be much, much higher than 6.6 MHz. (As I remember, the Hustler
used #14 close spaced on about 2" diameter to obtain a self-resonant frequency
at 6MHz.)

Cecil, I suggest you re-measure the self-resonant frequency of the coil by
itself, and if you have the means to do it, also measure the series resistance
at both the self-resonant frequency and at 4.0 MHz. I'm betting there will be a
large difference in the resistances, and that the self-resonant frequency will
be much greater than 6.6 MHz.

Walt