RadioBanter - View Single Post - Transformer for longwire antennas to reduce noise problem?

September 27th 04, 12:17 AM

On 26 Sep 2004 14:55:49 -0700, (TheGnome)
wrote:

I
managed to get 75 feet of #26 magnet wire on a perpendicular roof to
my window of my dorm room, and two runs of 15' speaker wire as a
counterpoise in my room. I'm getting a really bad noise problem

Hi OM,

Use coax out 25-30 of those 75 feet. At the far end, put your
counterpoise there and thus move your input to a position remote from
that same noise (presumably in your room). At that same far end, add
a 1:1 BalUn or W2DU style otherwise known as a Current BalUn rather
than a Voltage BalUn (the distinction in this regard is important).
This will keep noise from coupling to the outside of your coax and
funneling into the feedpoint (as long as your receiver has good
shielding). It is called "choking." This will help with radiative,
local noise. You can add a second BalUn on the antenna/counterpoise
side for Z transformation, if you choose.

If the noise is conductive, then it is coming in through your power
supply (AC is carrying trash). Good ground can help solve this,
unless you are in a room on a high floor. You can confirm conductive
noise by breaking all AC and ground paths and running on battery power
(if this is an option) or connecting your antenna to a battery powered
receiver. Another option (if no battery options are available) is to
get a long extension cord and try another outlet that you can identify
as being on a separate breaker (this may not be easy in a dorm
situation). With this, you may find a quiet AC branch that is not
shared with the noise generators.

73's
Richard Clark, KB7QHC