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

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

"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 Wed, 25 Jun 2008 16:17:18 GMT, "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
***GASP!***
Did you just invent a water-tuned variable inductor?

John Ferrell W8CCW
Beware of the dopeler effect (pronounced dope-ler).
That's where bad ideas seem good if they come at you
fast enough.

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

"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

"John Ferrell" wrote in message
...
On Wed, 25 Jun 2008 16:17:18 GMT, "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
***GASP!***
Did you just invent a water-tuned variable inductor?

John Ferrell W8CCW
Beware of the dopeler effect (pronounced dope-ler).
That's where bad ideas seem good if they come at you
fast enough.


Well, yeah - unintentionally, I guess. See my reply to Tom.

John

Would a section of 1/2" copper pipe work as a good choke? Simply slid
over the coax?

I've seen lightning chokes where about a 8ft piece of copper pipe was
slide over coax to choke off a lightning surge.

No Spam wrote:
Would a section of 1/2" copper pipe work as a good choke? Simply slid
over the coax?

I've seen lightning chokes where about a 8ft piece of copper pipe was
slide over coax to choke off a lightning surge.

If the pipe was attached at the outside of the coax, at the antenna feed
and have a length of 1/4, 1/2 wavelength, etc. (depending on antenna
type/length), I would suspect it would be an "easier" path for the rf
currents which were flowing on the outside of the coax, and they would
now choose the path of the pipe--wouldn't you? However, another way of
looking at this particular situation would be you just added another
element to the antenna!

However, I suspect you are suggesting chucking that (1/4?) wavelength of
pipe over the coax an no specific point and with no direct connection to
the coax; and, in that case, I would have to experiment, do research or
ask someone with experience ... however, I suspect not ...

Regards,
JS