"K7ITM" wrote in message
...
On Jun 25, 9:17 am, "John KD5YI" wrote:
In another thread, Richard said:

"You can achieve astonishingly high Zs with a coiled
transmission line with very little effort (roughly 8-12 turns on a
liter pop bottle - empty of course - for HF)."

The key is "...empty of course...". What if one were to fill the bottle
with
relatively pure water to keep dissipation factor low? Water's dielectric
constant is about 80. This would increase the stray capacitance, thus
reducing the required turns to achieve resonance. Would this increase the
Q
due to lower loss in the inductance?

Just curious.

John

Very unlikely. It won't increase the effective shunt capacitance all
that much since it's not between the turns, and it's not likely you'll
have pure enough water to have low loss in the water.

You can wind a coil that's self-resonant and achieve a high impedance
over a fairly broad range of frequencies (that is, across all of an HF
band), or you can use just a few turns (that is, a coil whose self
resonance is considerably higher than the operating frequency) and put
a tuning capacitor across the coil and tune it to a specific
frequency. That can be nice at lower frequencies where it takes a
long piece of line to make a self-resonant coil. In that case, the
impedance at resonance will be high, but the bandwidth will be
relatively small; it can use a lot less coax though. There are
programs and web sites that predict the self-resonant frequency of
solenoid coils, though with the coax jacket, expect the actual self-
resonance to be slightly lower than the same coil without the jacket.

Cheers,
Tom



I found 6 feet of RG58 and an empty plastic water bottle of about 2.7 inches
diameter. I got 8 close-wound turns of the coax on the bottle. I used my
Boonton Megacycle Meter to measure the self-resonant frequency of 43.8 MHz
with the bottle void of water. I then filled the bottle with distilled
water. The new frequency was 24.1 MHz. Wow! This is an increase of about 3.3
times in the stray capacitance. Even with the dielectric constant in the
center increasing 80 times, I didn't expect such a dramatic change.

The real question of Q remains unanswered. This was a quick test to see if
there may be enough change to warrant further study. But, it occurs to me
that the weight of the water would be entirely prohibitive if one wanted to
hang the water coil from an antenna.

Is there any place this might be used where the weight would not be a
problem? Does this warrant a closer look to measure Q?

John