[RFI] Testing The Effectiveness Of RF Chokes On Solar Panel Installations

[KD7JYK DM09]

"I also expected that they would test the level of RFI on each of the 
cables coming off each panel to see how effective the suppression was 
and to determine which chokes on which cables needed tweaking.  Isn't 
that how a professional engineer would approach this?"

Yes, even a decent tech, or fair hobbyist.

I have a dedicated monitoring setup.  It's for regional comms, a single 
frequency, in AM, with an 18" antenna on a scanner.  Comms are recorded 
and stored daily with a Sangean DAR-101 recorder.  Both pieces of 
equipment use linear power supplies, so no issue there.

There problem arose when I built an audio cable to run from the back of 
the scanner, to the two microphone jacks on the front of the recorder. 
All sorts of noise radiated from the cable, into the scanner antenna, 
just a few inches away.  As the installation is on a night stand, there 
isn't room to separate the equipment, and adding an external antenna, to 
get away from the noise source, brings in comms from other regions many 
tens of miles away, and out about 300 miles when conditions are good, 
which is highly undesirable.

The solution was two clamp-on ferrite chokes, one for each microphone 
cable.  I slapped them on at the recorder, right at the source, seemed 
to make sense.  That didn't work out too well.  I used an HT to sweep 
the cable with a tiny stubby little antenna, and found a "hot spot", the 
strongest RFI, about 6" from the recorder.  I moved the ferrites there. 
  Problem solved.  The scanner works at the threshold of squelch 
breaking, right next to an RFI spewing recorder, and has for about seven 
years, with no RFI issues.

I did the same in the shop, where I have an LED daylight "40W" bulb in a 
magnifier.  That is a rather poor installation, the magnifier is bolted 
to the wall, with the cable running up to the ceiling, and tapped into a 
light over the bench.  I just whacked-off the plug, and tapped into the 
box.  I like to monitor various things when in the shop, and RFI from 
this one bulb was an issue.  I set my HT to AM, and swept the cord, 
which is about 6' long, at various frequencies, 100, 150, 200, 250, et 
cetera, up to about 500 MHz.  I clamped on several ferrites, five or 
six, of various mixes, at the different hot spots along the cord.  Now, 
I can set the HT on the little shelf on the wall, within a foot or so of 
the noisy light/cord, without problems.

Kurt