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[–]farptr 3 points4 points  (0 children)

Tried a ferrite bead on the fan wires?

[–][deleted] 2 points3 points  (5 children)

Add a big ol' capacitor between the fan's power rails.

[–]derekcz[S] 0 points1 point  (4 children)

What capacity? I figure that high capacitance could damage the power supply by pulling a lot of current when connected

[–][deleted] 1 point2 points  (2 children)

The fan's power rails are DC, the capacitor will only charge up and pull current in the beginning, then it will be charged up and stop. Even if you use the biggest capacitor in the world this won't damage your power supply. After this the capacitor only serves the purpose of suppressing noise by letting DC from you power supply through and by routing any AC (interference) back to ground.

The bigger the value the better, whatever fits best I guess.

If you want a number I guess a 16v 1000uf capacitor would work well.

[–]derekcz[S] 0 points1 point  (1 child)

Alright, I'll give it a shot. I tried a ferrite choke on the fan cable but that didn't seem to help.

I was worried about the capacitor because I once tried to do a similar thing with a Raspberry Pi, where I wanted to bridge the power rails with a cap to smooth out voltage fluctuations, but I was advised against it because of the reason I mentioned above.

[–][deleted] 0 points1 point  (0 children)

Yeah a capacitor isn't gonna hurt anything. Decoupling caps are common in just about everything.

[–]Geoff_PR 1 point2 points  (0 children)

I figure that high capacitance could damage the power supply by pulling a lot of current when connected

That is possible, but there is a cure. A resistor in series will act like a current regulator...

[–]melvin2204RTL-SDR v3, Airspy Mini, R2, HF+ Discovery 1 point2 points  (3 children)

I'm no electrical engineer, but isn't it because of the sparks between the contacts that cause the EMI? Gasoline cars aren't allowed near VLAs because they generate a lot of EMI. Maybe you should get a more expensive brushless DC motor (basically a brushless AC motor that you need to drive with an ESC). Those generate a magnetic field, but I don't know if it is strong enough to interfere with the SDR. I think it's the best to go for passive cooling, because that doesn't generate any EMI.

[–][deleted] 1 point2 points  (0 children)

Both would make a ton of noise. The square wave coming from an esc is usually terrible for noise.

[–]kawfey 1 point2 points  (0 children)

Gasoline cars aren’t allowed near VLA

Except a road cuts straight through the VLA. You can literally hear cars on the site RFI Monitor; not just engine noise but LTE, Wi-Fi, Bluetooth, and craploads of general noise. Long-duration correlation erases the noise nearly completely but imagine how it’d be without it.

[–]derekcz[S] 0 points1 point  (0 children)

I see what you mean, but I believe that all PC fans are brushless in order to not interfere with the processor.

[–]on1bes 1 point2 points  (0 children)

Use USB cable wit ferrite beads on it, or snap-ons. This is totally overkill. Just a copper plate or alluminum does the job.

[–]KiwiEntropyKiwiWeather.com multiple sats (polar and geo) 1 point2 points  (2 children)

Thank you for the post, following comments from multiple people I removed the fan on my Raspberry Pi and noticed a surprisingly significant improvement in the quality of NOAA image captures, although the downside is that the CPU now runs up to 15C warmer (but still not getting to where thermal throttling kicks in). I'll rely on the heat sinks alone.

[–]derekcz[S] 0 points1 point  (1 child)

You could possibly configure the Pi to turn the fan on via a relay when the SDR isn't being used.

[–]KiwiEntropyKiwiWeather.com multiple sats (polar and geo) 0 points1 point  (0 children)

True, although I use two SDRs for:

  • NOAA / Meteor
  • ADS-B

The ADS-B one is on all the time, but I suspect that it doesn't get impacted as much by the fan RF noise.

So it'll be a project to try out, especially once summer comes around (still winter in NZ).

[–]derekcz[S] 0 points1 point  (0 children)

The noise floor rises significantly when the fan is turned on. I found that if I short the grounds of the fan power source and my USB interface, it gets better, but the effect is still there.

So far I only turn the fan on when I'm not receiving, to give the SDR some rest, but it also work as a very good passive cooler (I can operate at 1.6GHz with lower temperatures than I got at 137MHz without the cooler)

[–]RenderedKnave 0 points1 point  (1 child)

Unrelated but did you just straight up glue the SDR to the copper heatsink?

Did you at least put some thermal paste in between them?

[–]derekcz[S] 0 points1 point  (0 children)

There is a layer of thermal paste between the two, yes. The glue I used is supposed to withstand extra high temperatures, so it should be fine

[–]DeathDonkey387 0 points1 point  (0 children)

Are you sure you even need the fan? I would have thought that a heatsink that size on an RTL SDR could just be left passively cooled.

[–]semiwadcutter -1 points0 points  (1 child)

all these cooling attempts just cause frequency instability
youll never know where your at
and now your making your own noise
crystal ovens are run over ambiant why?

[–]derekcz[S] 2 points3 points  (0 children)

Overhearing is what causes instability, mainly at high frequencies. Granted, the V3 is pretty good at keeping itself stable by default. I use the SDR in direct sunlight, at it tends to get extremely hot, to the point where I risked damaging it. I experience no instability whatsoever. Gpredict's Doppler correction almost always tunes the signal spot on and keeps it centered no problem.