As it happens, I found myself at Quartsfest in Arizona in the latter half of January, 2026 where we set up some banners proclaiming the existence of the Northern Utah WebSDR (link) - but I also scribbled on a small white board the words "QRM-Free Solar is possible - Ask How!".
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| Figure 1: My humble, RF-quiet solar array at 2026 Quartzfest Click on the image for a larger version. |
Between the SDR, this message and the diverse portable HF antennas erected, I have had a lot of conversations over the past several days about these and many other topics, meeting new people and re-acquainting myself with others that I've seen on and off over the past several years of my attending QuartzFest (this is year #4 for me.)
RFI-less solar IS possible
During the "Solar Walkabout" - an on-foot tour to look at how others camping have deployed their solar panels - I volunteered to have folks look at what I'd set up: It's nothing obviously special - a glass-panel 200 watt Renogy folding array and another Renogy "flexible" solar array - but there is one major difference: It does NOT produce HF QRM, meaning that I can plant my portable antennas near my panels and not get any interference on HF.
As I've done some previous articles on this, what I'll present here is mostly a set of links to those articles with a quick overview, but this effectively puts that information in one, handy place.
Let's start with quieting the Renogy solar charge controllers:
Reducing QRM (interference) from a Renogy 200 watt (or any other!) portable solar panel system- Link
The main issue with Solar charge controllers is that you have a "dipole + transmitter" situation: The panels themselves do NOT cause RFI, but the charge controller is effectively a transmitter - especially if it's a PWM and/or MPPT-type - and the legs of the "dipole" are the solar panels (possibly long wires connected to large, rectangular pieces of metal) and another set of wires going to the battery - which also find their way around your RV/campsite via the inverters, DC wires, etc.: It is no surprise at all that RF finds its way out of these things! By adding filtering, we are effectively "shorting out" the the RF at the feedpoint of this hypothetical dipole and preventing it from radiating.
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| Figure 2: Filtering on the bottom of the Renogy controller making it RF-quiet. Click on the image for a larger version. |
To quiet these panels, I added bifilar-wound ferrite toroids - but also bypass capacitors: The toroids (ferrite) alone will probably knock down the QRM by 2-3 "S" Units, but if you are getting S-9+ interference from your solar, simply knocking it down to S-6 or S-7 when you are in the boondocks - where the natural noise floor is closer to S-1 or S-1 - is still pretty bad!
The key here is adding capacitors in addition to the ferrites and this method is perfectly capable of quieting even the noisiest of solar chargers. It is also vitally important to put this filtering physically close to the noisy device and use good-quality bypass capacitors.
While the above blog entry showed a modest (200 watt) system, the above can be scaled up for higher-power systems: Larger wire will handle more current and larger toroids will accommodate it!
RF Quieting a Samlex 150 watt Sine Wave inverter - Link
Another component of RV/camping with power is the inverter to run mains-voltage devices, and these can be terrible noise sources. The article above shows how it's possible to make one of these devices completely quiet. For the older Samlex inverter - which was terribly noisy out-of-the-box, it is now quiet enough that I can power LED Christmas lights from it that are strong from the same mast as the antenna and I get NO RFI (the LED Christmas themselves don't produce QRM).
I was fortunate that there was enough room in the Samlex's case to be able to add this filtering, but it may be added externally as well, provided that the leads are kept short.
What follows below are some methods for quieting UPSs (Uninterruptable Power Supplies). These are very much like the inverters in an RV in that they produce mains voltage from battery power - and the same problems with RFI occur:
A high-current DC (and AC) noise filter for UPS or RV use - Link
This shows a rather extreme example (an 8kVA UPS) where high currents are involved: Such would be the case with a kilowatt-class DC-AC inverter or even a large PV system.
Containing RF noise from a sine wave UPS - Link
This article shows the techniques involved in quieting a lower-power UPS, but it also introduces some other components: Rather than winding your own filter using toroids and wire, you can get "Line Filter" modules from electronic parts supplies (e.g. Digi-Key, Mouser) with brand names like "Corcom" or "Delta" (among many others.) These are self-contained modules with the components built-in - available in a wide variety of voltage and current ratings - that can do an excellent job of filtering.
Completely containing switching power supply RFI - Link
This is an extreme example, but it shows how one might be able to make even the noisiest switching power supply quiet - and this might be important to someone who is trying to get every device in their ham shack - whether it be at home or on the road - quiet. This method is foolproof in its effectiveness, but it is also likely overkill for many applications, but it discusses the "how and why" these techniques can work.
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I hope that this helps those who venture out in the wild with their RVs, solar power and battery system and still be able to operate HF.
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