HFU HF Underground
Technical Topics => Equipment => Topic started by: ChrisSmolinski on September 21, 2017, 1909 UTC
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Once again, I ran into a problem with QRM caused by an electronic device. Some hunting around with the AFE822x and Macbook (a portable SDR is very handy for hunting down QRM) found the culprit - the monitor of one of the kids' computers. Wrapping as many turns as possible of the monitor AC power cord around a large ferrite core seems to have eliminated the problem. No doubt a misbehaving switching power supply. Below are pictures of the core, as well as the before and after screenshots of the netSDR connected to the sky loop (not the portable AFE822x).
The core is a Fair Rite 5943003801, type 43, 35 mm inner diameter and 61 mm outer diameter. This is my go-to core for solving QRM/RFI issues. The best price I've found is from Mouser, about $4 each: http://www.mouser.com/ProductDetail/Fair-Rite/5943003801
The horizontal lines you see on the after screenshot are lightning from thunderstorms, which were not present on the first waterfall, taking several hours earlier
(https://i.imgur.com/OfopIUQ.png)
(https://i.imgur.com/vH4WUTF.jpg)
(https://i.imgur.com/1EFxw4S.jpg)
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Hello Chris,
Maybe you could do a little better.
The idea is that the 'in' and 'out' of the cable in the ring should be as far away from each other as possible.
I don't remember where I saw the drawing, with such a big ring.
I use that idea with smaller rings, but it's not the same cute design, and a picture would be of no help. Just finding a way to wind the cable in the ring so that the 'in' is never close to the 'out'.
Apart of that, for a mains AC cable, you can use a so-called 'lightning protector' *with an EMI-RFI filter*. Don't care too much of how many dB's are announced, as there are several ways to give a figure. They are useful from 100 kHz to 100 MHz approx. (not quite good at those limits), and the best filtering is around 10 MHz quite approximately. Once more, the 'out' should not run back near the 'in'.
Ray
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I know where you where coming from Chris, recently purchased a new Samsung Digital Inverter Technology refridgerator and it causes a massive 10dB over interference just about all over HF with spurs 8KHz a part.
Samsung was contacted and are sending a technician in coming days, was told by them that "it complies with Australian standards".
Also experienced hash type RF which was tracked to a wall mounted touch screen control panel for the ducted gas heating in the house, resolved this by climbing under the house and disconnecting it.
RF troubles never end... 8)
Full details/story found General Radio Discussion page.