[RFI] 160 meters RFI caused by low voltage bookcase lights

Paul Christensen w9ac at arrl.net
Tue Sep 30 12:53:01 EDT 2014

"Portable direction finding equipment :

DX440 receiver
W1FB adjustable preamp
Tuned 4 turn 13" diameter shielded loop (tuned to approximately 1.82 mhz)"


Great job finding the root cause.

Perhaps you can tell us more about the shielded loop used to triangulate the 
source?  Any articles or construction notes?

I have the National Vector Gun with the new 1.8 MHz loop together with an 
SDR-IQ receiver and notebook PC.  However, I'm finding that the preamp is 
adding more noise than signal.  The preamp peaks and tunes fine, but the 
noise floor covers up switching sources at the -110 dBm level.

I'm looking for a more efficient antenna for this purpose and may try a 
Pixel Loop for locating low-level switch-mode sources, then move to the Gun 
when getting close.  Your noise source was severe enough (S9+) that you 
overcame this issue with the small diameter loop.

I once owned a Palomar LA-1 loop system and that allowed me to locate many 
low level noise sources.  I sold it, thinking the Vector Gun would do a 
better job.  Hindsight is 20/20 and I should have kept the LA-1 before 
trying the Vector Gun.

Paul, W9AC 

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