Interference question
 

I just got a suitcase Zenith trans oceanic radio...when I first picked it up it received pretty good. After I recapped it the performance went way up. In my area there is some sort of on and off interference that does not have any pattern to it but reminds me of a fluorescent light with a bad ballast. On AM when the noise kicks in I can get only 2 local stations......the rest of the band is loud hum.....even on low volume. Is there anything I can do? When the hum is gone sometimes AM is clear and then other times background crackle .......

First make sure it isn't something in your house. The most common causes these days of this sort of interference include LED lights, and switching power supplies. I have one computer monitor which nearly takes out the AM band due to its cheap power supply.

First take the radio somewhere else & be sure its OK.
Then start throwing breakers one at a time. Use a transistor radio as a
noise detector. After you throw the main breaker use the radio to sniff out
the noise. It can still be in your house if its something battery op.
Take a walk around the area to pinpoint it. It can be quite far away.
At the shop we had an int buzz you could even see on a TV. The electric co made many trips & finally found something breaking down 1/2 mile
away.

73 Zeno:smoke:
LFOD !

Thank you, I will check. I haven't had a tube radio in my house for years because of this issue.

I was having the same issue with a couple of my battery operated radios and it turned out that those portable charging bricks that you can use to quickly recharge a cell phone or MP3 player (such as an iPod or even wireless earbuds or headphones) was putting out some interference which is interesting because they are strictly battery powered and shouldn't have to rely on a SMPS, but apparently they do (or at least something similar) so then I just try and keep those away from my radios.

Another weird thing about those portable charging bricks is that they seem to put out interference regardless of whether they are plugged in and charging and or charging something or not..:scratch2::nono:

Modern wall warts and 120V to USB chargers use switch mode power supplies and regulators instead of the 60Hz transformers and linear regulators they used 20 years ago.


Switch mode supplies typically use 17KHz square waves. As Fourrier proved mathematically a square wave is made up of sine waves... Specifically one at the fundamental and an infinite series of multiples of the fundamental each a higher frequency than the last. As frequency increases amplitude decreases, but radios are sensitive to very low amplitude.

The makers of these devices could keep the square waves from interfering by filtering and or shielding the supply to keep these signals from conducting down cables and or radiating, but many makers, especially China, simply don't care enough to do it.

For a while there I had some noise that was pegging the S meter on my Icom transceiver anytime I wanted to talk on 40/80M (7 mhz and 3.8mhz). Turned out to be the 12 volt switcher that fed my sat receiver. Swapped it out for another, problem solved! Somehow my solar setup isn't too noisy, which is surprising as I have one of those cheapo high frequency "pure sine" inverters. It's not grid tied if that makes a difference.

Yeah walk around the house and hunt for the noise and/or start flipping breakers.

I wasn't talking about a wall wart style charger, I was talking about the type that you can charge up and take with you to charge a phone or wireless earbuds when you don't have an AC wall wart to use, like the one pictured below.

Oh, a power bank....Those are switch mode too. Everything is these days.

OK, I didn't realize they had a Switch Mode Power Supply in them, it would explain why whenever I charge them or had one of them sitting near one of my battery powered radios that my battery powered radios went beserk reception wise...:scratch2:

I didn't even think about those being a source of noise. I had my (tr)usdx HF radio plugged into one yesterday (for lower power output while I was tuning the reference frequency). Luckily my power bank isn't noisy.

Good information here about this infernal annoyance. The oldest source of radio noise besides car ignitions, electric trolleys and motors with brushes are the classic lighting dimmer switches.

These https://www.bing.com/images/search?v...t=0&ajaxserp=0

Ah Yes Dimmer Switches, my parents have some dimmer switches in their house and I was staying over one night and I had brought my Zenith Trans-Oceanic with me to listen to some night time DX'ing and for some reason I kept hearing a bunch of hash noise on the radio while I was tuning across the dial and wouldn't you know it, it was coming from the old dimmer switch they had in their basement. :sigh:

The only time I found that a fluorescent T12 (pre-T8 and CFL) was causing AM buzz was a 2-foot shoplight that used a trigger start ballast, only because it wasn't grounded.

120/277-volt electronic ballasts were bad enough but now LED drivers of all shapes and sizes are suspect 1.

The house I grew up in had a dimmer on the lamp above the kitchen table in the dining area. I never had any issues with RFI from that dimmer, none at all. This was the only light dimmer in the house, the other switches being standard on/off switches. The dimmer on the lamp in the dining area never gave five minutes worth of trouble; in fact, if I remember correctly, that dimmer was still there when I moved to my apartment, 21 years ago.

I don't know what happened to the dimmer after I left the house; my best guess, however, is it may have been replaced with a standard on/off switch or perhaps another dimmer. I have absolutely no idea at this time what happened to the dimmer (or to anything else in the house, for that matter), as when I left the house for good in 1999 I did not look back.