Mains noise

Useful information regarding antennas for SDR products.
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Re: Mains noise

Postby CaptainNemo » Wed Sep 05, 2018 6:52 pm

Anyone has news about Phil? I hope it's all ok with his eye.

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Tom Atkinson
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Re: Mains noise

Postby Tom Atkinson » Sun Dec 30, 2018 12:35 pm

Really hope your eye is ok, Phil. Myself and many others (I'm sure) are waiting with bated breath for the next installments in this series. Really enjoying your writing, your humour, your expertise and experience. And really appreciating the graphics production effort you have gone to so far.

I got an RSP1A for Christmas and like many others, are now hard at work trying to reduce all that noise. I found 3 x switching power supplies yesterday that, when removed, reduced the HF noise by about 15 dB. I was ecstatic with this improvement, but want to go a lot further (have seen some of your screen captures of the RSP1A spectrum/noise floor and began uncontrollably drooling) .

And, am keenly following your advice re antenna. That horizontal "loop" you suggested is the sexiest antenna I have ever made (have made plenty of dipoles and long wires). Using speakerwire as the feeder at the moment, whilst I wait for the 300 ohm twin lead to arrive!
Last edited by Tom Atkinson on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Re: Mains noise

Postby arcosine » Sat Jan 12, 2019 2:15 pm

Phil, I hope your eye is getting better. Ive found that the USB chargers make noise, as well as LED lighting, florescent lights. Insulators on the main overhead wires can leak causing RFI (noise). If you find a noisy insulator you can call the power company and they will come out. I located mine with a 2 meter beam and an HT set to AM mode. I have one outdoor LED light that wipes out everything when turned on. I had DSL hooked up to the phone lines in the house and that caused a lot of noise. I now have the wireless modem/router where the underground line enters the house and that solve many issues, inducing speed.

Loop antennae have lower noise than whips due to responding to magnetic fields vs electric, and some noise can be null out. Your idea for a balanced line will work, if you make a toroid transformer at the antenna port, its easy. Ive used 300 ohm twin lead to a loop. The antenna side is not grounded. Place your antenna as far away as practical. Ferrite beads on noisy appliance cords also help.

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Re: Mains noise

Postby ON5HB » Sun Jan 13, 2019 10:27 pm

The first solution everybody should do is a common-mode-choke.

In short this is preventing that the outside of the coax/cable works like an antenna.

Most easy and cheap way to remove this is a big plastic bottle and wind coax around it, 20 turns or so and the effect is gone.
Naturally you do this at the antenna connection to the coax, not inside the home.

Other solution is using a 1:1 balun or put a load of ferrite clamps on the cable.

All of that removes unwanted reception, ergo house/man made noises.

Grounding antenna is rubbish, nobody does this, unless it's HF-ground....but that is not the same as household-ground!

Do not ground your stuff to electric ground as it does help reception but also increases rubbish.

Remove common-mode-currents, that is 80% or more won over everything.
Coax has 3 currents....2 inside and 1 outside....the outside is the problem...common-mode-choke solves that.

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