[RFI] in the shack rfi found!

David Robbins k1ttt at verizon.net
Mon Jan 16 15:59:53 EST 2017

This is a relatively odd case of noise from switching mode wall warts that
had passed all my initial tests, that is they didn't make hash that I could
pick up, until..


I had been plagued with some inter-station interference off and on for the
last couple years.  Last summer I replaced all the ferrite baluns on my 40m
and 20m stacks because I found they were overheating and several were
damaged. see: 

un    (note this page has lots of pictures and will take a while to load, it
shows some cracked binocular ferrites from an M^2 'balun')  The replacements
were just rg-213 coils.  This got rid of a bunch of noise from both 20m and
40m interfering with other bands.  But there was still more, but harder to


I recently rewired my receive antenna switching and filtering since I
determined there was a problem with not having a bandpass filter before the
preamps in some odd combinations.  This could have been the cause of some
noise. the one I found in particular was from 160m to 40m, though it could
likely have happened to other bands in a m/m contest.  This has all been
cleaned up now.


So, after doing all the above I did a test using my SO2R station to transmit
on one band and listen on the other bands on the 2nd radio.  As noted at the
start of the blog linked below the only bad one was from 80m to 40m.  While
it existed on all the 80m TX antennas it was worst on the low Inverted V
which is about 150' horizontal and 60' up from the shack. even when running
only 50w or so.  It was almost gone on the 4-square, except for the North
beam which aims at the shack.  And it could be picked up on all the 40m TX
and RX antennas though the levels varied with directions, but mostly worse
pointing towards the shack.  Continue with the blog:




David Robbins K1TTT
e-mail:  <mailto:k1ttt at arrl.net> mailto:k1ttt at arrl.net
web:  <http://wiki.k1ttt.net/> http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or  <telnet://k1ttt.net:7373>



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