[RFI] Coupling methods for RFI emission testing on SPS

[Jim Brown]

On Mon,8/8/2016 9:46 PM, Jeff AC0C wrote:
> Or maybe some other suggestions based on your experience.

Hi Jeff,

I recently went through this getting a small Samlex inverter to be clean 
enough to power a logging laptop for mobile use in W6GJB's pickup, and 
trying to find a switcher quiet enough (or make it quiet enough) to use 
in my shack. My tests in both cases were very practical, and limited to 
my specific conditions (that is, antenna farm, other RF noise). For 
Glen's truck, we set the laptop up with the Samlex inverter, then 
listened on the KX3 and looked at the PX3 with the truck's Hamstick on 
20 and 40M, in Glen's pasture, with the truck motor off. I did that 
during the day, when there was minimal propagated noise. We added 
suppression until we no longer saw/heard noise. You can see the results 
in the piece about killing RX noise on my website.

Next, just as a curiosity, I took that same setup into the shack and 
looked for RF noise in the closest antenna, a 160M Tee vertical that's 
about 25 ft from the operating desk. Also during the day, so minimum 
propagated QRN, only local sources. That antenna is the acid test for 
anything noisy, and no matter what I did, I couldn't even come close to 
cleaning up the Samlex enough to use it. No big deal -- I didn't NEED to 
use it there.

Next, I looked at a cheap 35A switcher that someone on the Elecraft 
reflector swore was clean. Not even close - I though a ton of ferrite on 
both the AC and DC lines, caps across the lines. Still at least 15dB 
above my noise floor!

With this setup, I heard very faint noise from the solar panels that are 
leaning on a sawhorse within a foot of that vertical when using the 
Genasun MPPT controller. Ten turns of #16 zip cord around a #31 toroid 
killed it.

I'm currently looking for a power supply to maintain the charge for the 
new 100Ah LiFePO4 battery that is now running my radios. As a temporary 
measure, I'm charging it with a spare power supply for one of my Lenovo 
laptops, feeding a Genasun Li MPPT charge regulator. That supply, rated 
5A at 20VDC, can put about 7.7A into the battery (thanks to MPPT 
processing in the Genasun), and was enough to keep up with SO2R during 
NAQP CW this weekend. I can't see/hear any noise from that combo in the 
160M vertical, but it's summer, and the propagated QRN from 
thunderstorms is at least 10 dB higher than the winter noise floor, so I 
don't consider it meaningful. OTOH, I could hear more than I could work 
during NAQP -- NR5M was solid here, but no joy.

So I guess what I'm saying is a practical test with our antennas that 
are most likely to hear the noise source, and at a time when other noise 
is at a minimum. My goal is to work the weak ones, the rare DX, the 
needed mults in a contest, so I want to see/hear NO increase in the 
noise floor under quiet band conditions.

Hope this helps.

73, Jim K9YC