VHF modulating neighbors speakers?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by WM5TS, Oct 28, 2014.

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  1. WM5TS

    WM5TS XML Subscriber QRZ Page

    I have been operating for about a year and a half and this is the first complaint I have gotten. I live on a 100' X 150" lot in a non HOA subdivision. I was checked into our club Monday night net which is around 145.000, I can't remember the exact frequency but this is close. Anyway he came over and said he could hear me on his computer speakers after he had shut down the PC. He said the speakers were powered and he could barely hear it but figured it must have been me.

    He was very nice about it and was kind of amazed that it happened. I asked him if he could understand what I was saying and he said it was very very low. My 2 meter rig is a new Kenwood V71A with an Arrow J pole in my attic. I was on low power.

    I was also running my ICOM 735 but on digital on 14.070 doing a PSK31 test to check propagation. This test is data and only runs for 10 seconds every 90 seconds. I stop it after three broadcast and check PSK reporter. The antenna for that one is an OCF dipole that has the last leg running along the property line. This antenna has only been up for a week.

    I have never heard anything in my home from any of my radios. I am only running the ICOM at 100W but was considering buying a 500W amp. Now I am not so sure. If he did indeed hear voice and not data then it had to be the Kenwood at 25W.

    I'm going to turn the last 20 feet of the OCF dipole back towards my yard for now but if anyone has some suggestions please shoot them my way. Everything is grounded and I have SWR numbers lower than 1.5:1 on the OCF and not sure on the Kenwood.

    Thanks;

    WM5TS
     
  2. K9ASE

    K9ASE XML Subscriber QRZ Page

    If you have attic antennas How does he know you're a ham? Never mind I just saw the answer.
    It's just a hunch but I think he doesn't like the looks of your dipole.
     
  3. KC9UDX

    KC9UDX Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    That's what my instinct says too. From what I read here, he heard "something" and didn't know what it was but knew exactly where it came from. I hope we're wrong.

    If the guy is really nice about it, he'll let you assist him in determining if it's really you he's hearing, and, he'll be reasonable about any solutions you suggest. Though I don't know why he would consider it a problem needing solved if the speakers are on with the computer off and he has to strain to hear something.

    The first thing I would do is get a Google Maps plot of other hams in the vicinity. I have this just in case something happens. There are multiple hams with powerful stations, with equally-scary-looking antennas close to my station. If there's nothing identifiable, the ambiguity may help. It would also be helpful to plot local broadcasters, GMRS users, and anything else that may cause this, like say the house with the Gizmotchy where the address isn't associated with any FCC licensee. :eek:
     
  4. K4ISR

    K4ISR Ham Member QRZ Page

    In my years as a computer tech, I have seen quite a few cheap unshielded speakers with this same problem. I actually have a set here where if I turn the volume down below 25%, the volume of the "interfering" commercial radio station goes up. So on the rarely used system I have them hooked up to, I turn the PC volume down and keep the speakers around 40-50% or higher. I did have a cheap ferrite choke on the line close to the speaker and it helped a lot, but not completely since the speakers themselves are also unshielded.
    There is not much you can do as the radio user, so it may help to find a quality set of speakers that specifically state they are shielded (or help him build a homemade shield like here: http://www.wikihow.com/Shield-Speakers )
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Impossible for speakers to demodulate FM.

    RFI can occur, but he wouldn't hear your voice. He might hear a hum or something.

    I'd say: Run some tests. Have someone else operate your rig while you go to the neighbor's house and see what's going on; if you don't have anyone else who can do this, you can run a recording of yourself, and play that through the radio (perfectly legal). I use one that says, "This is a test. WB2WIK testing for RFI. This is a test..." and just keeps playing that. You can do that lawfully.

    Normally, electronic devices that can "hear you talking" will only do so with amplitude modulated transmissions like AM or SSB. I've never in my life seen any demodulate FM, unless they're actually an FM receiver.
     
  6. W0AAT

    W0AAT XML Subscriber QRZ Page

    My PC speakers pick up HF thru 70cm, usually hum, on SSB it is somewhat modulated. After a handful of ferrites it is mostly gone to where I can ignore it.
     
  7. K4ISR

    K4ISR Ham Member QRZ Page

    Tell that to my computer speakers picking up 90.1 MHz FM radio station clearly as I turn the volume down. The volume knob is acting like a reverse potentiometer for the modulated RF coming in... so PC sound goes up and RF down as I turn the volume up, and then below 25% the lower I go, the louder the radio station up to a clear 30-40dB.
     
  8. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Put some chokes on the speaker cords at each end. Use at least three turns.
     
  9. K6IGB

    K6IGB Ham Member QRZ Page

    I agree. if it was in fact FM, then all he would hear is a humming or a clicking when you transmit and stop transmitting. In order for the speakers to demodulate the RF (read:detect) it owuld have to be some form of amplitude modulated signal. (AM / SSB) in fact, a lot of GSM phones can be heard through computer speakers because they use forms of modulation where the amplitude and frequency or phase change at the same time. Solution... use non powered speakers, wrap all the cords in ferrite where they enter the speaker that has the actual amplifier in it, and call it a day. I also agree with the others that have suggested that you double check to make sure it is actually YOU causing the R.F.I. .
     
  10. W0JMP

    W0JMP XML Subscriber QRZ Page

    Yes, by all means, first make sure it is indeed you'

    When my wife and I bought our first house and had been their about a month, an irate neighbor came to the door telling me I was "tearing up his TV" during a favorite program. How did he know it was me? By the call plates on my car.

    Only one problem; there was not one piece of ham gear in the house. When we lived in an apartment, I stored my radio gear in boxes in my grandmother's basement. With all the work on the house and a new baby, I did not yet have tome to get it out.

    I told him there was no ham radio equipment in the house. He was angry and adamant that I was causing his problem. I offered to let him come in and we would search the house together. That mollified him a bit and he just stomped off.

    Danny, W0JMP
     
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