"Cecil Moore" wrote in message
...
Reg Edwards wrote:
If the line is a whole number of 1/2-wavelengths, with a low
resistance ground the input impedance of the coaxial outer
conductor
will also be very low and longitudinal current in the line will be
at
a maximum. Insertion of the choke will be very effective.

To complicate things a little more, the common-mode current may
consist of standing waves. If the choke is installed at a current
minimum point, it may have little effect.
--
73, Cecil http://www.qsl.net/w5dxp
====================================

Dear Cec, It doesn't complicate things. It merely repeats what I have
already said. When the line is an odd number of 1/4-waves long and
there is an (albeit indeterminate) ground at the transmitter end, then
there will be a high impedance at the choke (DUE TO STANDING WAVES)
and the choke will then be wasting its time.

If you havn't, moons ago, already downloaded the program then do so
and read the program notes. There are so many unknowns in it the
results are only approximate but nevertheless sufficiently accurate
for the intended purpose - which is just to demonstrate choke
behaviour.

The only accurate result is the calculated-from-first-principles
self-capacitance of the coil on which the impedance/frequency response
depends.

I had checked calculations, years back, by winding many coils of
various sizes and shapes, (one 7 feet long), with various numbers of
turns and measuring the coils' self-resonant frequency over the HF
band using hand-held instruments with coils suspended in free space
from strings. I always knew the results would be useful at some time
or other, never even dreaming about choke baluns.

Did I ever tell you that for several years I was Head of a
Measurements Standards Laboratory which I personally set up from
scratch and which was in the 2nd echelon from the British National
Physical Laboratory. The NPL.

There were certain electrical parameters for which the laboratory was
capable of making measurements more accurate than the NPL but for
obvious political reasons it was not possible for the laboratory to
claim such performance on calibration certificates.

Some time after I had left the position on promotion, the wicked Mrs
Thatcher had the laboratory dismantled and sold it off in bits because
it did not produce any immediate, short-term profits. She was a
chemist who went into politics. Often I still wonder what happened to
the oven-enclosed battery of 12 standard Western cells.

One day, if I can force myself to find the time, I may write my
memoirs. I could tell you some amusing stories.
----
Yours, Reg, G4FGQ