Reg Edwards wrote:
But Cecil, maximum resistance, maximum reactance and maximum impedance
all occur at the same resonant frequency.

Reg, if you would learn the Smith Chart, you would know
that is not true. :-) At self-resonance, the inductive
reactance cancels the capacitive reactance leaving a
pure resistance usually of a few thousand ohms. But I
agree with you that a purely resistive self-resonant
choke is not a bad thing.
--
73, Cecil http://www.qsl.net/w5dxp

"Cecil Moore" wrote in message
...
Reg Edwards wrote:
But Cecil, maximum resistance, maximum reactance and maximum
impedance
all occur at the same resonant frequency.

Reg, if you would learn the Smith Chart, you would know
that is not true. :-) At self-resonance, the inductive
reactance cancels the capacitive reactance leaving a
pure resistance usually of a few thousand ohms. But I
agree with you that a purely resistive self-resonant
choke is not a bad thing.
--
73, Cecil http://www.qsl.net/w5dxp
======================================

Cec, I don't need a Smith Chart, and neither does anybody else, to
work out the resistance at resonance.

I don't think you quite know what you are doing with elementary
circuit analysis. The Smith Chart is giving you the wrong answer. The
resistance of a choke at HF at self resonance is in the order of a
megohm or more, not just a few thousand ohms.

By the way, what is the diameter and winding length of a USA pop
bottle.
----
Reg.

Reg Edwards wrote:
The
resistance of a choke at HF at self resonance is in the order of a
megohm or more, not just a few thousand ohms.

I just guessed at it, Reg, based on my measurements of
toroidal chokes and W2DU baluns.
--
73, Cecil http://www.qsl.net/w5dxp

Reg Edwards wrote:
By the way, what is the diameter and winding length of a USA pop
bottle.

The diameter of a 2 liter bottle is 4 inches. The Bible
says the ratio of circumference to diameter of a circle
is 3. :-) The length of the bottle is about a foot.
--
73, Cecil http://www.qsl.net/w5dxp

The diameter of a 2 liter bottle is 4 inches. The Bible
says the ratio of circumference to diameter of a circle
is 3. :-) The length of the bottle is about a foot.
--
73, Cecil http://www.qsl.net/w5dxp
============================================

Before publishing your rules of thumb you can check your reasoning by
using program SELFRES3. Download from website below.

I must admit, rules of thumb are quite adequate for coaxial chokes.
Almost anything will work. Very often things will work quite well
without a choke at all. ;o)
-----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

On Thu, 3 Aug 2006 03:37:05 +0100, "Reg Edwards"
wrote:

I must admit, rules of thumb are quite adequate for coaxial chokes.
Almost anything will work. Very often things will work quite well
without a choke at all. ;o)

But the Rule Of Thumb to avoid (presumably) parallel resonance of the
choke for the reasons given is ROT.

Owen
--

Owen Duffy wrote:
On Thu, 3 Aug 2006 03:37:05 +0100, "Reg Edwards"
wrote:

I must admit, rules of thumb are quite adequate for coaxial chokes.
Almost anything will work. Very often things will work quite well
without a choke at all. ;o)

But the Rule Of Thumb to avoid (presumably) parallel resonance of the
choke for the reasons given is ROT.

Wouldn't the resonant circulating currents be at their
highest magnitudes at the parallel resonant point and
therefore the I^2*R losses in the coil be greater at
that frequency than on either side of self-resonance?
(I explained that avoiding self resonance is only a
personal preference.)
--
73, Cecil http://www.qsl.net/w5dxp

"Cecil Moore" wrote in message
.. .
Owen Duffy wrote:
On Thu, 3 Aug 2006 03:37:05 +0100, "Reg Edwards"
wrote:

I must admit, rules of thumb are quite adequate for coaxial chokes.
Almost anything will work. Very often things will work quite well
without a choke at all. ;o)

But the Rule Of Thumb to avoid (presumably) parallel resonance of the
choke for the reasons given is ROT.

Wouldn't the resonant circulating currents be at their
highest magnitudes at the parallel resonant point and
therefore the I^2*R losses in the coil be greater at
that frequency than on either side of self-resonance?
(I explained that avoiding self resonance is only a
personal preference.)
--
73, Cecil http://www.qsl.net/w5dxp

Hi Cecil

Doesnt the increase of impedance of the parallel resonant "balun"
discourage current from flowing into it? I considered that the source
impedance is constant and the "balun" impedance rises as resonance is
approached.
I figured the circulating current would be Q times the current thru it,
but the current thru it drops as its impedance rises.

If I'm wrong, I've been lucky so far.

Jerry

"Cecil Moore" wrote

Wouldn't the resonant circulating currents be at their
highest magnitudes at the parallel resonant point and
therefore the I^2*R losses in the coil be greater at
that frequency than on either side of self-resonance?
(I explained that avoiding self resonance is only a
personal preference.)
======================================
Hi Cec,

The exceedingly small power loss in the choke depends on the impedance
of the power source which is driving it. It is a question of
non-conjugate mis-matching. But at self-resonance, and indeed
anywhere else, you can forget all about power loss. Especially as no
ferrite material is involved.

If you have bothered to check your "rule-of-thumb" and
"turns-per-metre-of-wavelength" against program SELFRES3, then,
provided results are in the same ball-park, all will be more than
satisfactory. SELFRES3 is itself only approximate. The choke's
self-resonant frequency is somewhat indeterminate as soon as anything
is connected to it.

A hank of a bunched number of turns is quite good enough as a coaxial
choke. It is only necessary to know the number of turns and the
diameter. Construction neatness helps with estimating the number of
turns but has hardly any effect on performance.

Coaxial chokes are a relatively unimportant circuit component.
Exactly what they are supposed to do is aways doubtful unless they are
used as baluns. I wonder why I am spending so much time discussing
the subject. Praps it's because I have nothing better to do.
smiley
----
Reg.

Owen Duffy wrote:
But the Rule Of Thumb to avoid (presumably) parallel resonance of the
choke for the reasons given is ROT.

The self-resonance to be avoided is 1/2WL self-resonance,
e.g. 20 turns on 10m. I apologize for confusing the two
self-resonant concepts.
--
73, Cecil, http://www.qsl.net/w5dxp