[TenTec] RFI Problem

[ve7asr@telus.net (Rick Williams)]

I use my computer at the rig for logging and playing.  When I replaced the
monitor with a Samsung LCD I lost almost 80 to 90% of the hash.

However, now that the noise floor was significantly lowered I found I had
another problem that I eventually tracked down to the computer's switching
power supply.  Unlike other birdies the power supply would slowly move up or
down the band -- especially on 80 metres.

I fixed the supply with a brute force filter on the AC line constructed
inside the power supply housing.  The filter consisted of two windings of
#18 wire on a 1 inch #43 toroid core.  I wound about 12 turns (I think --
it's been a while) and the choke measured about 180 uH.  I spliced this into
the AC line and added bypass caps (0.05 mf) from the AC lines to ground.

The components are not critical just make sure the caps are 500 volts or
better.

The results were dramatic.  The computer power supply noise is gone and I
can even listen to my 1930 Philco when the computer is running.

73,
Rick
VE7ASR