I have a car antenne with 50 Ohm coax that I want to
connect to an old radio
with a 300 Ohm balanced input so I need a balun and
impedance converter. Any
info about how to build one will be welcome. (Being
an amateur I don't want
to buy one.)
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Dear Pieter, pleased to meet you.

The first thing to say is that the impedance of the
short length of coax line between antenna and receiver
has very little to do with the unbalanced-to-balanced
transformer between coax and receiver input. The coax
is just a short length of wire between antenna and
receiver with a relatively small capacitance between
the the wire and ground.

To design a transformer more information is needed. But
whatever it is it will be a very easy to make. All you
will need is a small ferrite ring and a length of thin
enamelled copper wire.

What range of frequencies would you like your receiver
to cover? Long-waves, medium-waves, short-waves or VHF
FM

What sort of antenna are you using? Is it a simple
vertical whip connected directly to the coax.?

Is anything connected betwen the antenna and coax? How
high is the whip. Is the height of the whip
adjustable.

Please provide more information and the number of turns
of wire on what size ring can then be decided.
----
Reg, G4FGQ