"Cecil Moore" wrote in message
. ..
Reg Edwards wrote:
Why avoid the self-resonant frequency?
That's the frequency at which the choking impedance is a maximum.

Personal preference - I would rather the choking impedance
be at maximum reactance rather than at maximum resistance.
I think that saves a little bit of power.
--
73, Cecil http://www.qsl.net/w5dxp
=====================================

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

And at the resonant frequency minimum loss occurs in the choke anyway.
There's negligible loss of power in the choke left to save.
----
Reg.

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

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