>Dielectric and o.d. of the coax both affect resonance. I have no data
>for RG142, but I suggest that you start with the guidelines for
RG59/RG8X.
>
>73, Jim K9YC
Thanks for last night's QSO in CQWW RTTY, Jim (with GM3W).
A small clarification while waiting for 20m to wake up...
The dielectric of the coax which affects the choke resonance is only
that of the outer jacket.
Along with the o.d. of the coax and the precise layout of the turns, the
dielectric of the outer jacket will affect the capacitance between
turns, and three of those factors will affect the choke resonance. That
is a very good reason to:
* Use "cookbook" designs from someone like K9YC, G3TXQ or myself, who
has actually measured those resonant frequencies (which requires some
special techniques in addition to owning a VNWA)
.and.
* Choose a broadband design which will be more tolerant of small
differences in winding layout and the unavoidable stray reactances when
you actually install the choke
.and.
* Copy that cookbook design EXACTLY - including the coax and the layout
of the turns.
I agree with K5GO about normally preferring a cable with a stranded
copper center conductor in preference to silver-plated solid steel, if
available. But if this is different from the original cable in the
cookbook design, it needs to be a very close alternative with the same
OD and outer jacket, and you should still aim for exactly the same
layout of turns.
73 from Ian GM3SEK
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