I’m using a PV system with a SolarEdge inverter, SolarEdge optimizers and Solar Frontier PV-panels. The system is quite close to the antenna of my ground station as you can see on my ground station picture. The observation below is made at sunrise, you can see what the PV system does to my reception when it switches on. Unfortunately the interference is in-band, so band pass filtering is not making the situation any better.
Does anyone have any ideas to improve the situation (that don’t involve dismantling the PV system )?
Another observation where the effect is visible: Observation 155277
Shield the inverter. Put a metal sheet between inverter and antenna, like a reflector.
OR you could put it in a metal box and bury it deep down near the earth core
Okay, I tried the following things:
- Run the setup on batteries and wifi to eliminate any conducted noise, the only outside connection is the antenna now.
- Add band pass filters (yes, multiple) to avoid overloading the frontend with out-of-band noise
- Add an LNA (SPF5189z) and lower the SDR gain to see if it would handle big noise signals better
- Add ferrite on the coax sleeve to eliminate common mode currents
- Play around with the gain to find a sweet spot for SNR.
At least now I know that the noise is received via the antenna and is actual in-band noise.
The best result I can get is this:
Observation of NOAA 19 with PV-system on/off/on
It is a bit better than it was, but the SNR is still sh*t when the system is on.
A next step would be shielding the inverter, but if it is the DC-leads that are radiating I think I’m out of luck. Don’t get a PV-system if you plan to receive anything during day time.
Realistically the only way to resolve the radiated noise is with filtering between the inverter(s?) and the panels. (Or, y’know, put the antennas a long way away…)
Filters to go on the DC side of solar inverters do exist (a quick google indicates Schaffner as one company that makes them). AC-side filters are also easily available. Both would likely require a licensed electrician to install.
You may get some reduction using clamp-on ferrites (and probably lots of). I’m unsure if it will be common mode or differential mode noise (which may change where to place the ferrites for best effect).
Filtering on the DC-side is tricky, the inverter communicates with the power optimizer modules mounted under the panels by modulating some signal on the DC-lines, filtering out everything non-DC will break this. Filtering on the AC-side is feasible though.
I think my next step will be walking around with an rtlsdr and a small probe antenna to try to figure out more precisely where the noise comes from. AC-lines? Inverter housing? DC-lines? All of the above? I will post here once I know more, maybe it will help someone in the future.
When I got my first HF radio a few months ago, this is EXACTLY how I found the S9 noise that was killing my 20m and 40m Rx. Surprised it worked - just used an RTL-SDR.com dongle (w/ a 2m/70cm HT whip) in direct sampling mode + GQRX, and it lead me right to my Samsung refrigerator display! Of course, the solution in this case was to move the antenna 100 feet away, though. Good luck!
I have made some progress, I will describe it here for documentation purposes, maybe it can help others that are battling interference.
I decided to try another approach and construct an antenna that is less prone to local interference. It is well known that a horizontal dipole over a conducting ground screen has a deep null towards the horizon, rendering it less sensitive to local interference. Furthermore the ground screen blocks any interference that comes from below the antenna, so if the antenna is mounted higher than the noise source it should not be picked up.
To test this hypothesis I put about 2x3m of chicken wire on a flat part of the roof and mounted a quick and dirty single dipole about 3/8 wl over it and scheduled some observations. The results are not bad, this observation is from this morning when the PV-system was just switching on:
Observation 248381: Fox-1A using dipole-and-screen antenna, PV-system switching on and off
You can still clearly see the noise floor rising when the PV-system switches on, but the effect is not as pronounced as in earlier observations. It could well be that the interference is now picked up by the cheap RG-58 feed line that I’m using in this quick 'n dirty setup. I will try eliminating the feed line by mounting the SDR at the dipole, to see if that helps. This will definitely help getting the SNR up. Of course this antenna is not very suitable for low passes because of the null at the horizon, but anything over 20 degrees should be OK.
To be continued.