If there’s anything more annoying to an amateur radio operator than noise, we’re not sure what it could be. We’re talking about radio frequency noise, of course, the random broadband emissions that threaten to make it almost impossible to work the bands and pick out weak signals. This man-made interference is known as “QRM” in ham parlance, and it has become almost intolerable of late, as poorly engineered switch-mode power supplies have become more common.
But hams love a technical challenge, so when a nasty case of QRM raised its ugly head, [Kevin Loughlin (KB9RLW)] fought back. With an unacceptable noise floor of S8, he went on a search for the guilty party, and in the simplest way possible — he started flipping circuit breakers. Sure, he could have pulled out something fancier like a TinySA spectrum analyzer, but with his HF rig on and blasting white noise, it was far easier to just work through the circuits one by one to narrow the source down. His noise problem went away with the living room breaker, which led to pulling plugs one by one until he located the culprit: a Roomba vacuum’s charging station.
Yes, this is a simple trick, but one that’s worth remembering as at least a first pass when QRM problems creep up. It probably won’t help if the source is coming from a neighbor’s house, but it’s a least worth a shot before going to more involved steps. As for remediation, [Kevin] opts to just unplug the Roomba when he wants to work the bands, but if you find that something like an Ethernet cable is causing your QRM issue, you might have to try different measures.
I was going to say on/off + binary search, but this sly fox is way ahead of me!
Every communication device these days using some sort of radio signal (WiFi,TV, mobile phone…etc) It’s one of those things that people not realise but technology not evolve as much as people think it did just been “upgraded”…
The FT817, ugh! 😮💨 The FT817 might be an egg-legging wool milk pig, but it’s not exactly very good at shortwave.
Except for PSK31 or FT-8 modes, were signal stability is more important than the rest.
Compared to an classic RF rig, like the FT-101, it’s deef and has poor modulation.
And it’s weak, too. It has less power than a tube era transceiver running off the driver tube. And worse large signal behavior.
For shortwave, I think, it should be nicknamed “FT-8-doesn’t work”. ;)
To be fair, though, the FT-857 unit was fine. It was the bigger brother and had meaningful output power level.
The 817 and 857 had a similar display.
That was it.
Even the reproduction tables where different. After Winelands mod on theb817 you have access to 220. Can’t be done on the 857.
Die eierlegende Wollmilchsau, richtig?
Wow this turned into a weird flame war. I will say that I got involved with (trying) to get some video game cabinets field UL listed, and yeah many of the suspiciously lightweight MeenWhale knockoff switching PSUs were leaky and wouldn’t pass. Replaced them with Meanwells and everyone got passing grades. So no, they’re not all created equally, and what you get on Amazon is automatically suspicious until proven otherwise.
And as for QRM, my house is FULL of switchmode supplies, but I managed to get lucky by accident I guess.. not one of them gives me any serious trouble on any band, except my 3D printer which is only used intermittently and my POE cameras, but I can filter that stuff with a notch on the radio, so.. no big whoop. Also, having the right balun on the antenna helps for some reason.
I just don’t feel they’re worthy of all the shade people are throwing. Yeah some are garbage, and there are lots of good reasons to get rid of those ones, so by all means, send them away. But to dismiss them as a class altogether seems silly.
Now for my radio, I definitely have a linear supply, because in theory they’re quieter, but mostly I realize because it looked badass with the big analog meters and was sitting next to the radio I bought and it was on sale. But I think a switcher would have been fine.
It’s hard to separate the supply from the electronics, too. It’s not like you get “super-well designed ultra-quiet electronics” coupled with “super-cheap switching supply” all that often.
We do some RF testing in our lab that’s at thermal noise levels (handy having an anechoic chamber 15 feet from your office to get down to -174 dBm/Hz) – most of the time the stuff that’s garbage is bad with its original supply and straight DC.
You also have supplies which in and of themselves aren’t that bad, but aren’t good at dealing with the typical crap on an AC line (their input filtering sucks): feed the DC they are providing into the anechoic chamber (from outside AC) and they’re terrible, run them off the filtered AC inside the chamber and they clean up a ton.
hello mr obvious.
I, for one, welcome the knowledge & experience of Mr Obvious.
Back when I was about 10, I started listening to shortwave radio. I was often frustrated by wideband hash noise. One day I was listening and heard the noise start right as the living room lights across the street went on. The noise changed as the lights dimmed. I went over the next day and explained what was happening. I threw a wire up into the trees and tuned in a VoA broadcast from Europe and then had him turn the light on. He was astonished! I offered to replace his ancient dimmer with a new one. (Yeah, I was a weird kid, I actually rode to radio shack and bought a dimmer with my own $.) I added a 22pf cap across the dimmer when I installed it. I had done that to all the dimmers in my house after discovering that this got rid of the last of the noise even a good residential grade dimmer made. That got rid of a huge noise source and made my listening a lot less frustrating. I checked the rest of the dimmers in his house, but none of them were even close to that living room in noise contribution. Unfortunately it seems that today even very expensive devices have some very poorly designed power supplies. The power supply for my CPAP caused so much interference that I almost had to stay up all night for my granddaughter’s sleep study! There is no good reason why a device that cost several thousand dollars should have such a poorly made power supply. The neighbor even asked me to turn in Russian broadcasts when there were rumors that something had happened. It seems the rumors were at least not totally bogus because the news segments were skipped. All they were transmitting was classical music.
Definitely easy fix for any ham radio as all ham radios works on same principles.Just on & off it and adjust frequency for station also antenna should be adjusted for best signal.
Equipment-generated noise is usually called QRN. This is opposed to QRM which is interference results from competing transmissions.