AM radio signal injected to mains - Page 1
Forum section: electronics / general

author: electr_peter
author_rank: Unknown
timestamp: September 06, 2015, 01:30:16 pm
content: HAM radio operator admits he was a bit naughty on the video.Stan Gibilisco tells a story when he intentionally injected high power AM modulated audio signal on 120 VAC house mains system (!!!) to create audio signal on stereo system (operated by annoying neighbour) in 1979.To me it seems a bit dangerous and crazy to even attempt. Any comments about the capability to do such thing in current times with HAM equipment, potential dangers, effectiveness of it to create audio on stereo systems, etc.?

author: SeanB
author_rank: Super Contributor
timestamp: September 06, 2015, 01:39:46 pm
content: Well, it is done with POE comms all the time, and they claim it has no effect on the other equipment all sharing the local supply grid.

author: electr_peter
author_rank: Unknown
timestamp: September 06, 2015, 01:53:16 pm
content: POE does not transfer any power at all compared to what this HAM radio operator did.I think high power high frequency AC can manifest as clock jitter on mains frequency clocks, stress mains input filters and disturb lamp dimmer circuits. High power motors/heaters/other equipment would not care at all. Such event can probably be a bad day for volt-nuts and sensitive RF equipment though.

author: SeanB
author_rank: Super Contributor
timestamp: September 06, 2015, 02:15:05 pm
content: Industrial areas with high power RF heating does nasty things to the local mains supply, though the power transformer at the final MV section to LV does do a good job of filtering this ( along with the high capacitance of the MV cabling) from being fed back up the system, and the utility PFC capacitors finish off the job making the power line draw look like a close to resistive load.PLT does have high power, though not at the tens of watts level, and most of the time the noise is wideband noise so it does not appear to be caused by the PLT stuff, even as it raises the local Rf background noise to S7 levels over the whole band from 100kHz to 200MHz.That they say the PLT stuff is only confined in the actual wiring is false, it will radiate. The only reason that the testing passes is they test a __**SINGLE**__ unit in an isolated chamber, where it does of course not transmit. Take 2 into the chamber, along with 200m of power cord, the stuff they sell at the hardware store, not the most expensive shielded cable you can find, and you will have a very different result transferring data between the 2 devices.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 06, 2015, 09:22:44 pm
content: I did something similar against a next door neighbor in a dorm with a noisy stereo, though I did it with a motor run cap, a loop of wire, and a SCR. Charge up the cap to 340V or so with a voltage doubler from an isolation transformer, then discharge it through the loop with a few neon bulbs to trigger the SCR. Range is quite short, but it only needed to reach next door so it did the trick.

author: aargee
author_rank: Frequent Contributor
timestamp: September 07, 2015, 12:21:45 am
content: Many years ago I had an older (crap, probably my current age) neighbor who used to listen to an AM radio station, that played countryandwestern music continuously, pretty loudly, some week nights and most weekends.He'd turn it down when requested for a short time but it'd just take one of his gazillion favorites to show up on the radio and it would be up loud again for the duration. His consumption of alcohol probably didn't help with his ability to make rational decisions either.Eventually we had enough. I got out my signal generator tuned to the AM radio frequency, modulated it with 1kHz and connected a long loop antenna. If the music got too loud, the sig gen went on, the radio blarted out 1kHz and the volume went down, the sig gen went off... eventually.Eventually, he came around for some advice about his radio that 'was playing up'. Knowing I was one of those electronic nerdy types, he thought I help him out.Pretty much told him that the radio was getting old and overloading when the volume was turned up for any length of time. He was happy with that explanation and the radio never seemed to be a problem after that.

author: tautech
author_rank: Super Contributor
timestamp: September 07, 2015, 12:25:43 am
content: Quote from: aargee on September 07, 2015, 12:21:45 amNice.

author: Red Squirrel
author_rank: Super Contributor
timestamp: September 07, 2015, 02:37:25 am
content: My back yard neighbour CONSTANTLY has his radio on full blast. Summer is short, so I'm not one to complain about someone that wants to enjoy the little nice weather we get, but it's gotten a little out of hand. I work shifts so sometimes I can't even sleep because it's on too loud and I can hear the muffling through the walls. I usually turn on the furnace blower and a fan and can mostly drown it out though so I just learned to put up with it. It's crossed my mind to build a FM transmitter to tell him to turn it down, or just mess with him though.