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
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