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why

Discussion in 'On-Air Operations - Q&A' started by BD5QCE, Sep 25, 2019.

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  1. BD5QCE

    BD5QCE Ham Member QRZ Page

    [媒体=的YouTube] WTZ-w4EPbqs [/媒体]
    1190khz
    3570khz
     
    Last edited: Sep 25, 2019
  2. BD5QCE

    BD5QCE Ham Member QRZ Page

    1190khz 3570khz
     
  3. WR2E

    WR2E Ham Member QRZ Page

    because you are close to the transmitter and are hearing the 3rd harmonic of the broadcast station.
     
    W7UUU and K7TRF like this.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Yup, and it's possible that third harmonic is being generated right in the receiver front end especially if the noise blanker is enabled.
     
  5. K8JD

    K8JD Ham Member QRZ Page

    Some AM stations are poorly maintained because all the money goes into FM HD and subchannels.
    I could hear the third harmonic of a 5 kW station on 1270 khz, very well, S5, on 80 m, 5 miles away.
     
  6. WA8NVW

    WA8NVW Ham Member QRZ Page

    @K8JD: Don't assume that your problem was caused by poor station maintenance. The FCC's out-of-band harmonic suppression requirement for that AM broadcast station is 70 dB. The transmitter starts now with a 50 kW carrier (+47 dBw), which means the 3rd harmonic is legal at -23 dBw, equating to 5 milliwatts. You can't filter their harmonic out because that's your desired receive frequency.
     
    K0UO likes this.
  7. K8JD

    K8JD Ham Member QRZ Page

    My example was a top notch, ABC owned station and I worked there at the time . as well as we kept things, some 3rd harmonic still leaked out. (I also had a good receiver and antenna up !)
     

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