"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

Hi Tom

What do you suppose would happen if the bottle had some steel wool in it
and (maybe) have a few less turns?

Jerry KD6JDJ

On Jun 25, 10:54 am, "Jerry" wrote:
"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

Hi Tom

What do you suppose would happen if the bottle had some steel wool in it
and (maybe) have a few less turns?

Jerry KD6JDJ

Well, shoot, if you put enough (common-mode) current in the coil, you
might be able to get the steel wool to catch on fire...

Honestly, I've had good enough experiences just using "air core" coils
of line as chokes, and in rare cases where I had a lot of RF to get
rid of putting a resonating capacitor across the coil, that I haven't
ever found it worth worrying about putting things into the coil as a
'core'. At this point I should perhaps ask, is the choke intended to
be dissipative, or reflective? Should it be just a high impedance so
very little current is allowed at that point, or should it look like a
resistive load? My ideal is high impedances at enough points along
conductors that aren't supposed to be radiating that the currents on
those conductors remain low.

Cheers,
Tom