Discussion in 'On-Air Operations - Q&A' started by BD5QCE, Sep 25, 2019.
[媒体=的YouTube] WTZ-w4EPbqs [/媒体]
because you are close to the transmitter and are hearing the 3rd harmonic of the broadcast station.
Yup, and it's possible that third harmonic is being generated right in the receiver front end especially if the noise blanker is enabled.
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.
@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.
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 !)