VHF modulating neighbors speakers?

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

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  1. K0RGR

    K0RGR Premium Subscriber QRZ Page

    Now that you mention it, I had a set of Altec Lansing computer speakers and subwoofer that did unexpected things. They would demodulate an FSK or PSK signal - I still don't understand how that worked, but it did. I don't remember it caring about 2 meters at all, though.
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    Slope detection of FM on an AM receiver is definitely an accepted method of detecting an FM (or PM) signal. What WIK was suggesting would definitely result in receiving the FM station.

    Back in the early 1970s, there was even one manufacturer of amateur radio FM equipment that used slope detection rather than a discriminator for the receiver. In the late 1940s, and well into the 1950s, when NBFM was relatively popular on HF, slope detection was used by the majority of operators to receive the signals. There were FM receiving adapters available, and several of the "top end" receiver manufacturers had optional FM detectors available for certain receivers as in my Collins 75A-3.

    Glen, K9STH
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I think it is, if you tune to the center carrier frequency with no offset at all.

    Using a simple diode detector and a tuned circuit to "tune in" an FM signal, if the diode detects any modulation, that means there really is an AM component to the transmitted signal. A "receiver" can also be used, you just have to be careful.
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    It is all FM to me.

    Black Magic is no match.
  5. KK4YWN

    KK4YWN Ham Member QRZ Page

    Well... After taking a peek at the schematic of slope detector, I'm thinking the switching power supply is the culprit. Look for demodulated audio on the DC.
  6. VE3KUT

    VE3KUT Ham Member QRZ Page

    Nope, no TV at home... This is strictly an audio system with extensive noise proofing. Only the sub does it too.
  7. AI3V

    AI3V Ham Member QRZ Page

    There is absolutly nothing wrong with your station.

    Interference to amplified speakers is 100% the fault of the speakers.

    Unless you can run less power, or use an antenna that does not radiate so much in the direction of the speakers nothing you do will reduce the interference. It,the interference is caused by the speakers acting as a "crystal radio"

    Try some ferrite on the speaker wires or a different brand of speaker.

  8. WB5WSV

    WB5WSV Ham Member QRZ Page

    I had a pair of powered computer speakers plugged into my TV because it had too low an audio output. And one night I awoke to hear a strange voice. It was CB, coming quite clearly over the speakers, which were still turned on even though the TV was off.

    It is possible that the neighbor had turned off the computer but the amplified speakers were still powered up - most are powered by wall warts and you have to either remember to turn off the speakers separately or use a master power strip and turn it off too.

  9. K8JD

    K8JD Ham Member QRZ Page

    Selective interference?
    Kind of curious as to why that particular station is getting into your speakers when it is 25.3 miles from your QTH, when there are several other FM transmitters around located within 11 miles, a lot closer? Some of the closer stations are the same 50 KW power level as 90.1. Also the signal from WTJT has to cross a couple of ridges to get to you.

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