RPi radiated noise on 144MHz

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g8gtz
Posts: 1733
Joined: Wed Apr 07, 2010 6:26 pm

RPi radiated noise on 144MHz

Post by g8gtz » Sat Jul 03, 2021 11:00 am

This has been discussed on air but not sure there is a forum topic running on it.

Now we are running the Langstone NB transceiver several of us are finding the RPi radiates 59+ noise on 2 metres. Presumably, this was not so noticeable with DATV receivers but must be affecting receive performance particularly on 146.5 but also possibly 50 and 70MHz.

So what can be done about it?

My simple investigations show the radiation is coming from a number of places but the display and possibly the ribbon cable driving it are very noisy, particularly on the Portsdown home screen which has some very bright areas - you can hear the noise change between screens on top of the background hash.

I found earthing the RPi4 USB connectors also reduces it but leads and the metal heatsink still radiate.

I have managed to take the noise from one system, which is built into a metal 19" enclosure, down to a manageable level but my microwave transverter driver system which has the RPi mounted on the back of the screen in a plastic housing - the one with the camera mounted the wrong way - is still very noisy. It closes the squelch on a noise free talkback FM signal on 144.750!

Other than putting it all in a metal box, I wonder if coating everything in aluminium coated sticky tape (£7 from Screwfix and designed for heating ducts) might help although there may not be a common earth.

And I have proven most of the noise comes from the RPi and screen and not ebay switched regulators!

Any other ideas?

73

Noel - G8GTZ

G3VZV
Posts: 36
Joined: Mon Feb 25, 2008 12:38 am

Re: RPi radiated noise on 144MHz

Post by G3VZV » Sat Jul 03, 2021 1:07 pm

Hi Noel,
I have been using a Rpi4 with a FUNcube dongle to receive 145MHz telemetry signals from the FUNcube spacecraft and the system performance seems on a par with a PC system that runs in parallel...maybe i just lucky!
73
Graham

G7JTT
Posts: 338
Joined: Fri Jun 10, 2016 5:05 pm

Re: RPi radiated noise on 144MHz

Post by G7JTT » Tue Jul 06, 2021 10:51 am

Has anyone actually looked on a spectrum analyser to see what frequency the RPi/screen etc radiate on ? As I only seem to have issues on 2m on my FT 7900 my FT 897 seems fine ?

73 John G7JTT

g0mjw
Posts: 2330
Joined: Sat Sep 20, 2014 9:15 am

Re: RPi radiated noise on 144MHz

Post by g0mjw » Tue Jul 06, 2021 3:12 pm

G3VZV wrote:
Sat Jul 03, 2021 1:07 pm
Hi Noel,
I have been using a Rpi4 with a FUNcube dongle to receive 145MHz telemetry signals from the FUNcube spacecraft and the system performance seems on a par with a PC system that runs in parallel...maybe i just lucky!
73
Graham
You are lucky - it doesn't work for me - but in this case I think it is the 7" screen or its cables that are radiating. Put it in a screened metal box making sure to ground the screen.

Mike

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