I have been experimenting with the K3's synchronous AM feature and was wondering about why I am hearing a background "roar" whenever I tune in an AM broadcast station that is running HD. The "roar" is not something supersonic, but is heard right through the audio that runs from 30Hz to 5kHz. I am a broadcast engineer dealing with AM transmitters, and am familiar with the AM HD transmission techniques. The HD sidebands are located approximately 6 to 17 kHz removed from the carrier, are about 20db down from the carrier, and when detected on an AM envelope detector, are heard as a "hiss". I was thinking that if the K3's bandwidth was narrowed to less than 6 kHz, using both the 6 kHz roofing filter and the DSP filtering, the digital HD sidebands would simply be unheard since they would fall outside of the bandwidth of the receiver. Using the K3 in standard AM mode, thats just what happens, you hear no "roar" underlying the detected audio. However when switched to either synchronous mode or USB or LSB in SSB mode, those HD sidebands appear to be causing that "roar" in the detected audio. That also got me to wondering what effects other spurious signals near an AM (or SSB) signal would be audible or detectable as "noise" or any other artifact in the detected audio. Has anyone else found this to be happening on their K3's in synchronous AM or SSB modes? Ted W8IXY [email protected]_ (mailto:[email protected]) ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected]
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