So, just when I got all happy that I had dramatically improved my HF reception.. - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: July 01, 2017, 09:38:24 pm
content: This RFI just started, and its worse than Ive ever had it before..I'm pretty sure its not my computer or power supply (I didn't change anything!) but unfortunately, I don't have any means of receiving signals right now thats not wedded to my desktop so I cant really check..Ive gone around the house turning other things off to see if that effected the noise and so far no luck. Because of my SDR hobby everything in the house that produces RF noise is already got ferrites on it and has the power cords coiled up tight, etc.So now its been there 24/7 for several days now.I've had varying degrees of RFI problems before and have had interference that resembled this before but its never been even remotely as strong.Does anybody have any guesses as to what it might be? I used a monochrome color map for the images to show what it looks like on the waterfall.On my RTLSDR the signal strength describes a slow increase and then decrease in signal strength.The rise and fall cycle is around ten seconds.Does anybody have any favorite tips to identify sources of strong HF interference generally?

author: piranha32
author_rank: Unknown
timestamp: July 01, 2017, 10:44:35 pm
content: Did your neighbor buy a PLC device?

author: xrunner
author_rank: Super Contributor
timestamp: July 01, 2017, 11:06:21 pm
content: I've had weird issues like that before. Usually it's a bad something-or-other in the house. I had a clock that did nasty RFI once, had to throw it away.Can you turn off all power in your house? Try that and if it goes away then sniff it out with a laptop w/SDR attached USB. Gottta be some device in the house if it goes away with all power off. If not ... be a lot more trouble ahead.

author: WastelandTek
author_rank: Frequent Contributor
timestamp: July 01, 2017, 11:14:21 pm
content: the environment has become so damn noisy of late it is just sadwon hung lo switching power supplies with 11 total components everywhere

author: voltz
author_rank: Frequent Contributor
timestamp: July 02, 2017, 12:07:34 pm
content: One trick is to make a sniffer probe. A long enough length of coax like rg58, then make a single small loop at the end from screen to inner.Connect it to your SDR and go walk about. With luck you will find a large signal at the source of the RFI.

author: cdev
author_rank: Super Contributor
timestamp: July 04, 2017, 04:02:20 am
content: Ive done that a bunch of times and thats how I eliminated all of the "low hanging fruit" at the beginning, but this particular noise is hard to get rid of that way because "its everywhere".Ive managed to reduce it a bit, enough for me to listen between the spikes on Linrad, sort of. But the noise is still everywhere bleeding into the audio.

author: AG6QR
author_rank: Frequent Contributor
timestamp: July 04, 2017, 04:35:11 am
content: The usual way to troubleshoot is to use a battery operated receiver, then switch off all the power to the house, and see if that killed the noise. If so, switch circuits on one at a time until the noise returns. If killing the power to your house doesn't fix the problem, then the problem is probably not in your house. Walk around your neighborhood.Many noise sources are broadband. If you have a portable AM radio, can you hear the noise on it when you tune to an "empty" portion of the band?If the noise only appears on HF, and if you genuinely have no way to receive except via your computer, then can you run the computer off an inverter powered by a 12V battery (from a car, perhaps)? Or if that's not practical, try this: Shut off all branch circuits in your house except the one powering the computer. If that doesn't eliminate the noise, then shut off the computer circuit, and turn on ONE other branch circuit, and run an extension cord from that branch circuit to your computer.But consider getting a battery operated portable receiver. Nothing beats the ability to walk around while chasing noise sources. The CountyComm GP-5 is a very portable shortwave receiver that features SSB. The Icom IC-R6 is twice the price, but significantly smaller, has AM but lacks SSB -- however, it has much broader frequency coverage, featuring UHF and VHF, and is also a full-featured scanner for FM communications. There are many other portable choices.

author: icept
author_rank: Newbie
timestamp: July 08, 2017, 04:41:11 pm
content: Quote from: cdev on July 04, 2017, 04:02:20 amA few 'out there' ideas if you've eliminated the low hanging fruit:-disconnect your antenna and make sure the noise disappears and is not internally generated or coming in on your power supply. Also try 50 ohm terminations or sig-gens if you have them-connect an HF low pass filter between your receiver and antenna to make sure the noise is actually HF and not aliased from a higher frequency. A low pass filter should have no effect if it is truly HF noise-find/borrow a laptop so that you can move around with your receiver to try and localize the source.-The rise and fall cycle of 10 seconds could be a clue, seems like air conditioners and refrigerators might cycle over these periods. Did the appearance of the noise correspond with hot weather?Good luck!

author: retrolefty
author_rank: Super Contributor
timestamp: July 09, 2017, 02:26:07 am
content: I once heard a talk at a ham club by a electric utilities interference troubleshooter. He said a AM portable radio tuned off station was the best method they found to hunt down "noisy hardware" on power poles. So if you can first locate such a noise maker a call to them will usually get attention.

author: cdev
author_rank: Super Contributor
timestamp: July 09, 2017, 04:18:34 am
content: I have a perfect radio for interference location, its battery operated but its old and it recently died. Its a realistic DX-370 that I have had for decades.. Its basically a Sangean. I am almost certain the problem has got to be a leaky or old capacitor. I probably even have an appropriate capacitor. Just need to get it opened up and do it. It covers AM BCB, as well as 3.2 to 7.3 MHz and 9.5 to 21.75 MHz, plus FM BCB.It would be worth fixing for both AM/Shortwave and also as its FM/FM stereo tuner is quite good.Ive managed to whittle down the noise quite a bit but its still there. yes, it did come out in a major way in the hot weather but we've had some good rainfall since then and the noise has been reduced a great deal.. Which makes me suspect grounding is involved.if it is the power system, and I suspect it may be, if I can narrow it down to a single pole, I am sure I could get them to fix it.I went and priced some ground rods and they want around $20 each for them, (and we already have several on the house power system) so I think I am going to try to make my own out of thick wire. several shorter, smaller spikes pushed down a few feet into wetter areas of soil tied together with soldered-on wire might be better than an additional big one for the purpose of SWLing.

author: jh15
author_rank: Frequent Contributor
timestamp: July 09, 2017, 05:35:38 am
content: In the old days, one was told to go around the street with an am radio tuned to around 800khz or so and hit utility poles with a baseball bat.You would hear a change when hitting the bad pole.The problem is, if there is bad hardware, a cracked insulator, you might bring it down on you, so not recommended anymore.Probably you'd be arrested for terrorism these days anyway.

author: cdev
author_rank: Super Contributor
timestamp: July 09, 2017, 01:22:11 pm
content: I think I am going to try using a combination of homemade radials and stripped thick green ground wire pressed into the ground near downspouts (so wetter)Dry ground may be part of the problem.My current activities just require a quiet pole for a PA0RDT style mini whip. PA0RDT type (FET amplified) e-field antenna is inherently less noisy, especially if its shield can have a grounding point outside away from house and electronics and then ideally a common mode choke in/on the coax on the way into the living space. I don't do a lot of shortwave listening any more, used to do much more of it. I mostly just listen to hams. Most of the news on shortwave is gone now. Shortwave radio, sadly seems to be dying thanks to the Internet.Growing up, the news was interesting for hearing a variety of different perspectives. Even just subtle changes like the UK (BBC) vs. US media. Also sometimes I like listening to CW or digital modes just for the ambient sounds.

author: CopperCone
author_rank: Super Contributor
timestamp: July 09, 2017, 06:40:41 pm
content: LMFAOimagine some old gray beard with a baseball bat attacking poles? cops would probably think he is off his medication.this could be also used as a clandestine transmitter for street thugshey tommy, send the signal.

author: ebastler
author_rank: Super Contributor
timestamp: July 09, 2017, 06:51:45 pm
content: Quote from: cdev on July 09, 2017, 01:22:11 pmSounds like your current setup is reasonably portable (or at least luggable). Can't you try a change of location, setting up your antenna, SDR receiver and computer at a friend's place temporarily? That might help to rule out your own computer and power supply as the culprits.