On Sun, 28 Aug 2005 12:59:40 -0700, Ron D'Eau Claire wrote: >Are you suggesting that those low frequencies are somehow being distorted >or causing other problems in the audio I.C. in the K2 before they get to >the filter?
Distorted no. Causing problems -- well, sort of. We don't transmit that LF audio (below the bandwidth of the xtal filters), but it does hit the comp/limiter and cause it to reduce the gain on LF peaks (which also reduces total modulation). So the result is less than ideal operation of the comp/limiter, which in turn results in lower average modulation and less audio punch. So the purpose of moving the low-cut up in frequency is simply to remove that LF energy so that it doesn't hit the comp/lim chip. Think of it this way. Speech energy is distributed between roughly 100 Hz and 8 kHz, but the 1 kHz, 2 kHz, and 4 kHz octave bands provide the greatest speech intelligibility. 500 Hz provides a bit, so does 8 kHz. the 250 Hz octave band and below provides virtually none -- BUT they consume a lot of power if we transmit them. We cannot transmit any of the 4 kHz or 8 kHz octave bands. So it makes sense not to waste any of our limited transmitter power on that energy below about 300 Hz -- it doesn't help us land that DX, or get through noise. All it does is give more body to our voices. So it is simply a matter of wasted RF power! >AM broadcasters were allowed exactly twice the bandwidth - 10 KHz - for music.) Actually, AM broadcasting in the old days (before about 15 years ago) was permitted to go to 15 kHz AUDIO bandwidth, which is 30 kHz occupied bandwidth. Current practice is 10 kHz audio, 20 kHz occupied bandwidth, but I don't recall if that was an actual rules change. The 2.6 kHz upper limit on SSB audio is just plain stupid. Yes, ham radio followed commercial practice. But that doesn't make it GOOD practice. :) Even POTS (plain old telco lines) goes above 3 kHz before it drops like a brick wall! Telco bandwidth is roughly 2.6-2.8 kHz, but it's 500 Hz to over 3 kHz, and it's not 6 dB down at those points! 73, Jim K9YC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
