Helping a friend with his RFI problem.

He has a SDR HF radio and Hustler BTV antenna with a toroid choke and about 32-radials. He has vertical bars on his panadaptor around 20 khz apart, mainly on 40M.

Disconnecting the antenna at the radio-end the bars go away, unscrewing the PL-259 so only the centre-pin is connected the RFI is mostly gone, fully connecting the PL-259 the bars are there.

Disconnected the coax at the antenna end, bars are also gone (thus i don't think this is common-mode RFI on the coax).

We've deduced his RFI is getting into his system from a radial wire ran under the BTV with RFI coming from a neighbours device (he's going to disconnect bunches of radials to triangulate which neighbour is the source of the RFI).

As this RFI is entering the system from a wire (radial(s)) and transported inside the coax, rather than the outer-shield, is there anything he can do on his equipment to remove this RFI?

As far as i know, the only solution would be for him to track the noisy device and put some ferrites on them, assuming a compliant neighbour. Did i miss anything?

Thanks :)

  • 2
    $\begingroup$ I'm curious about this radial wire from the neighbor's device that runs under your friend's antenna. It sounds as though the neighbor is also a ham with a vertical, and one of the neighbor's radials runs under your friend's antenna. Is that right? (Editing the question might be better than answering with a comment.) $\endgroup$
    – rclocher3
    Aug 18, 2020 at 15:52
  • $\begingroup$ Adjusted the question to be a bit clearer, but the radial(s) are his own, it just extends to his fence-line and we currently think it's picking up the RFI from a neighbours device (yet of unknown origin). $\endgroup$
    – t252
    Aug 19, 2020 at 10:13

1 Answer 1


You might look into a noise cancelling device. The principle of operation on this is to use a second antenna to 1) capture the same noise but phase shifted 180º and 2) mix/add to the primary antenna's signal to leave just the desired signal.

The second antenna doesn't need to be huge or effective... in fact, if it's not very sensitive and the only thing it picks up is the RFI, that will be perfect for your application. And as Mike points out in the comments below, placed and oriented to pick up the RFI as strongly as possible.

The product link I shared is to an MFJ product I've never used, but there are other manufacturers or you can home-brew your own.

I know this doesn't directly answer how to find the RFI source, but hopefully this will help you in getting to what you really want anyway: RFI out of your receiver!

  • 1
    $\begingroup$ I have an MFJ-1025 and can testify that this is a good answer to part of the question. However, the noise antenna should be placed where it picks up as much of the RFI as possible. $\endgroup$ Aug 20, 2020 at 12:48
  • 1
    $\begingroup$ Great point Mike, edited my answer to incorporate it. $\endgroup$
    – webmarc
    Aug 20, 2020 at 15:10

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .