Help with RFI coming from my PC please!

[SpaceForceCmdr]

I've been getting a low, pulsing hum on certain stations (happens a lot around 4840 and the surrounding areas). I was pulling my hair out, but I think I figured it out. It's not interference from my home electrical system or various electronics: it's my dang PC! I connected my SDR (HF+ Discovery) to my laptop, but used the same antenna. Bingo! The hum is gone.

However, I'd prefer to use my PC for listening, so is there a way I can somehow connect it but eliminate this hum? The USB cable that came with my HF+ does have little cylinders at each end, but it doesn't seem to matter. If I use a plain, old USB cable, the hum remains Any advice would be greatly appreciated!!

 

[majoco]

I found the same some time ago, but it wasn't the PC, it was the monitor power supply. Turning the monitor off at the front panel pushbutton didn't fix it so I though it must be something else but of course the power supply is still going. Pulled the power plug out and noise gone. Found a monitor in an op shop for $10 and....no noise!

 

[SpaceForceCmdr]

Thanks, that is a possibility. I'll investigate.

 

[prcguy]

You might try running your SDR from a laptop then make an RF probe with a very small turn or several turns of wire at the end of some coax from center conductor to ground. Then sniff around the suspect computer while watching a spectral display so see what computer cable(s) are the worst offenders. Then you can wrap those cables around some ferrite with the proper number of turns for the ferrite mix and frequency range of interest.

 

[SpaceForceCmdr]

Thanks, all! I did figure out that even though my PC is causing some noise, it's not the culprit when it comes to the low humming I'm hearing. I think some of it may be due to the LED light bulbs in my room, but not sure that's the only cause. I narrowed it down to the breaker that controls most of the light switches on my first floor, but there's some weirdness going on. Even with the breaker off, if I flipped on the switch in my room, the hum would return. There shouldn't be any power going to it, so WTH?

 

[ecps92]

Quick thought is a bad ground, time to get an electrician in to check out the wiring

Thanks, all! I did figure out that even though my PC is causing some noise, it's not the culprit when it comes to the low humming I'm hearing. I think some of it may be due to the LED light bulbs in my room, but not sure that's the only cause. I narrowed it down to the breaker that controls most of the light switches on my first floor, but there's some weirdness going on. Even with the breaker off, if I flipped on the switch in my room, the hum would return. There shouldn't be any power going to it, so WTH?

 

[Carter911]

Or stop by Lowes, Ace Hardware, etc., and get one of their outlet checkers.
You plug it in and the LEDs in the device tell you if Hot & Neutral are correct or reversed, and if the Ground connection is good.

I found my (Cannon) laser printer/ scanner device's power supply was radiating EMI.
Not an easy one to fix.

JC

 

[K4EET]

For the price, when compared to its analog cousins, I would get a digital Electrical Outlet Checker like this one:

https://www.lowes.com/pd/Kobalt-Digital-30-250V-Test-Meter/1001799404

 

[ecps92]

problem is, the OP said a Light Switch
Best to leave the 120v issues to the Licensed professionals

Or stop by Lowes, Ace Hardware, etc., and get one of their outlet checkers.
You plug it in and the LEDs in the device tell you if Hot & Neutral are correct or reversed, and if the Ground connection is good.

I found my (Cannon) laser printer/ scanner device's power supply was radiating EMI.
Not an easy one to fix.

JC

 

[K4EET]

<snip>
Best to leave the 120v issues to the Licensed professionals

That is good advice but it doesn’t hurt to know the “health” of the electrical system so one can speak intelligently to the professionals. The more they think you know about their trade, the less likely they will try to charge you for things you don’t need.

As for Electrical Outlet Testers, I found this one at Amazon that is a name brand tool maker and it even measures the time it takes for a GFCI to activate. And it costs under $20 USD.

Amazon.com

 

[prcguy]

A good ground or lack of one probably has nothing to do with your noise. Noise doesn't know its supposed to travel only to ground so usually it goes everywhere on every conductor. You need to either use an RF sniffer as described to find where the noise is coming from or on the computer itself try ferrites on various cables in and out of the computer and watch for a reduction in noise. You don't want to guess how the noise is getting to your receiver, you want to know precisely how it gets there so you can actually fix it.

On the circuit breaker being off but a switch on that circuit causing noise, when you flip a switch it is connecting or disconnecting a wire back to the associated circuit breaker. If noise is present in the main circuit breaker panel it can travel throughout the house wiring. Noise can easily couple to other wiring in a circuit breaker box and it could be when you turn a wall switch on its connecting more wire that is acting like an antenna bringing the coupled noise closer to your antenna.

Quick thought is a bad ground, time to get an electrician in to check out the wiring

 

[SpaceForceCmdr]

I picked up a multimeter to make sure the dimmer in my dining room was hooked up correctly. It was impossible to tell visually because both wires coming out of the box are black. I ended up replacing the dimmer just for the heck of it. Anyway, with the new one, it doesn't matter which wire goes to which. However, it also has a green ground wire, like my old dimmer, and that can't connect to anything since there is no ground wire in the box. I was originally thinking I could ground it to the box, but thanks to my handy new meter, I determined that the metal box is not grounded.

I think my electrical system is a bit wonky in this house. It was built in the 30's, and the wiring was apparently updated at some point before I bought it. It looks like it was knob and tube before that. I thought all the knob and tube was disconnected, but there are some wires in my basement that are hot (when I use the non contact feature on my meter, it lights up). Also, some of my outlets are the grounded kind (with 3 holes), and some are only 2 holes.

And then there's this fun little access panel in my hallway on the first floor. There's a mix of old and new wires, and only some tape with numbers on it, so not sure what any of it goes to.



As far as grounding, there are a couple of copper wires coming off the main panel in the basement. One goes out through a hole in the basement wall below ground level, and the other runs over to the water main and it bolted to it.

 

[dlwtrunked]

Light dimmers and radio never do well together. I have none in my house and am willing to pay neighbors not to have any.

 

[DS506]

some of my outlets are the grounded kind (with 3 holes)

Does not necessarily mean they are connected to a ground wire that goes back to the panel... Someone could have opted to replace the outlet instead of using ground adapters.

 

[SpaceForceCmdr]

I didn't check all the 3-prongs, but the ones I did check (with a multimeter) do appear to be grounded. If I put a probe in the hot hole, and one in ground, I read 122V or so.

 

[K4EET]

I didn't check all the 3-prongs, but the ones I did check (with a multimeter) do appear to be grounded. If I put a probe in the hot hole, and one in ground, I read 122V or so.

Still may not be a separate ground and could be jumpered to the neutral. You really need one of those under $20 electrical outlet tester to know for sure. I ordered the Klein RT250 GFCI Outlet Tester from Amazon Prime and got it the next day to replace my antique tester that didn’t do as much. The Klein RT250 is rock solid construction and performs like a champ!