Station RFI Both Ways

Submitted by KC3PFR on Thu, 03/11/2021 - 23:08
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Dear Elmer,

I started operating HF this year and have a 100W station with an EFHW 80-10 antenna. Station works great, but I have a couple RFI issues that I could use some advice on:

1) Even before I had the station, I used the antenna on an SDR receiver. Both my radio and the SDR are regularly overwhelmed by a pulsing RFI signal across all the bands. I can attenuate the noise, but it dramatically impacts enjoyment. Based on pattern of life of the signal, I suspect it is a neighbor's television set. (mostly on evenings and weekends, but not exclusively so. Not timed with sun rise / set, not ever present, etc.) What is the best way to track this down? I back to a number of houses.

2) On the transmitting side, a neighbor put out a call to a neighborhood facebook group asking if anyone was a HAM operator. Needless to say, she didn't want to inquire about getting a license. She is apparently a voice artist and recently bought some new headphones and could hear me clearly in them while working. (She sent a recording.) I obviously reached out and offered any assistance I could provide and agreed to help her troubleshoot. She said she ordered a new cable that is gold plated, but I'm a little worried that won't do the trick. I've had a couple issues with my own computer speakers and an old boombox around the house, but figured that was a proximity thing. I must be interfering with other neighbors as well? Anything I can do other than deconflict with her use of her headphones or suggest she keep trying other pairs?

Thanks in advance!

73,

KC3PFR, Brian

K3EEZ - Fri, 03/12/2021 - 05:38

On number 1, are you sure it's not coming from your own house, in other words, have you shut off power to everything (except the receiver of course power that by battery if you can).

Re number 2, are you sure it's her headphones and not the amp (or whatever last stage she's plugged into). It may be possible to add filtering to get rid of the noise. I had a similar problem of hearing my own transmissions through amplified speakers for my SDR. I tried adding ferrite cores to cables, new twisted pair cables, and so on, and finally when I added low pass filters to the outputs of the amplifier I reduced the noise to almost nothing.

KC3PFR - Fri, 03/12/2021 - 23:01

Thanks! Yes, I've shut my house down to nothing at the breaker and still had the same interference on a battery powered laptop with an SDR receiver into my antenna. It shows the same pattern of use on the laptop, so I am confident it is coming from outside the home. I'll try to record some samples with and without.

Not sure on part 2. I haven't been over to look yet. She is willing to test with me. The only indication that I have form her about the headphones is that she just got them. I've been operating for a while now and this is the first complaint, so if I am lucky her headphones solve it.

 

Thanks for the filter idea. I have a similar issue on my computer speakers, so I'll try something along those lines.

KA3LXM - Sat, 03/13/2021 - 07:02

Brian -

Look at your close neighbors roofs... Solar Panel circuitry has also been identified as a source of RFI. 

jim

KA3LXM

K3RSJ - Sun, 03/14/2021 - 13:07

An AM transistor radio is still an effective means of detecting RFI. Years ago I heard advice" "Never operate a linear w/o a LP filter". Still good advce which I always have followed. BGE will come out and survey for RFI. but only report and take action on their equipment. Contact thru main call center, they will route your message to the RFI guy. He came out quickly for me, but it was a guy with a cheap battery tender which I detected myself with the trusty AM radio. Gud luck!

KC3PFR - Sat, 03/20/2021 - 15:37

After some troubleshooting with my neighbor on the number "2" problem above, we've narrowed it down to 40 meters. None of the other HF bands appear to give her issues. I may give her some ferrites, but I suspect that might still leave some residual signal on her recordings. In any event, I've found some space to operate without concern for her and can deconflict 40m operations. Will keep you all posted. Thanks for all of the ideas both here and offline that I have received.

K3EEZ - Sun, 03/21/2021 - 07:33

Did you also try 15M?