On 6 Sep, 15:09, Cecil Moore wrote:
skk203 wrote:
Could anybody let me know how to contruct a bulun to match a longwire
antenna to a receiver. A step by step guide would be appreciated as I
am a non technical person.

The design impedance of a balun is determined by
taking the square root of (the input impedance
multiplied by the output impedance). Do you know
the output impedance?
--
I think that the OP is not referring to a balun, but instead to an 'un-
un'. This is, in this application, a
9:1 impedance transformer used to 'match' a long(ish) wire to 50 or
75
ohms. A typical use is with an inverted-L antenna, where the feedpoint
is
remote from the house, and coax is used to bring the signal back to
the
shack. The advantage of this arrangement is that the antenna usually
picks
up much less interference from domestic electrical sources. It's
essentially a receive-only device, but can be used for low power
transmit (so I'm told).

The transformer is usually wound with a 3:1 turns ratio, on a ferrite
ring or
rod and, using the correct grade of ferrite and actual number of
turns, it is
possible to obtain a frequency range of 1 to 30MHz (ie the whole of MW
and
SW spectrum).

Of course, the 'matching' is only approximate. It's just that, at
most
frequencies, the insertion of the transformer provides a better match
between the coax and the antenna than you would have if there was
simply
a direct connection. It makes no attempt to be an antenna tuner. For
some
information, may I direct the OP to a recent thread in this newsgroup
(1
August), the subject of which was "UNUN Cores?How To Wind?". The OP
was "Greg ".

And then there's Google. There are a few useful links he
http://groups.google.com/group/rec.radio.shortwave/msg/
1abc6a2bf8acc12d