"i4jmy@iol.it" wrote:
> Again, the mechanism of an antenna choke it's not that of a transmission
> line. Behaviour of a transmission line (when not resistively terminated into
> it?s own characteristic impedance) is to cyclically show high and low
> impedances, and repeatedly change in reactance sign, with an EXACT harmonical
> relation.
I missed this one on the first reading.
The behaviour you described is that of a "lossless uniform transmission line",
uniform meaning constant characteristic impedance accross the line length.
However, there are transmission lines that are neither lossless, nor uniform.
Their resonances are not strictly harmonically related.
(By "there are" I don't mean they are available commercially :-)
A choke as a transmission line has varying characteristic impedance
across the line length (measured from terminals toward center).
Average characteristic impedance runs into several kOhms for HF amp chokes,
less for RG213 baluns.
A moderate-loss choke behaves just like you described:
"cyclically show high and low impedances,
and repeatedly change in reactance sign",
although resonant frequencies are not in EXACT harmonical relation
due to non-uniform characteristic impedance.
A heavy-loss choke has more deformed resonances,
some of them may be missing, even the reactance
sign may stay the same on both sides of impedance minima/maxima.
This is all as predicted by good old Shelkunoff's
theory of non-uniform transmission lines.
73,
Sinisa YT1NT, VA3TTN
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|