About line:
First of all, a low loss TV coax cable is not necessarily better (or is only
marginally better) than an RG58.
This happens because at low frequencies the losses are mainly due to
conductors resistance, and only marginally related to dielectric type.
A foam dielectric but same conductors resistance, won't give any improvement
at low HF.
Often, domestic TV coax cables (including those for SAT use) are quite poor
in terms of ohmic shield conductivity. Thin metallized plastic films and
very few thin copper wires are not good ohmic replacements of
a good copper shield at HF.
Moreover, foam is inherently prone to get contaminated, and foam cables
without a solid and strong outer jacket are much more delicate than those
with compact dielectric.
Such features are definitely not the best for a very long line, may be
laying on the ground, and to be used at low HF.
Best replacements for a 300m long RG58 line are 1/2 " or bigger hardlines
and definitely a symple RG213 is
already a very consistent progress.
About impedance:
Plugging a 75 Ohm source into a 50 Ohm load (the receiver) doesn't produce
by itself any dramatical effect.
In the real, what should be measured with complex loads (antennas) is the
impedance at line connector that's not necessarily that of the nominal line
value.
Absolutely not related with line quality, the impedance could be quite
different than espected at that point.
It might happen, expecially if beverage transformers won't have the correct
ratio, and line lenght is not a multiple of wavelenght, that transormed
impedance is far away the line or receiver values.
In the case the line lenght is close to a quarter waveleght (or odd
multiples) the above finds its worst case.
73,
Mauri I4JMY (one of IR4T)
i4jmy@iol.it
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