This is admittedly topic skew, but for non-critical occasional am listening, it would be nice to have a much lower cost option than the $120 filters. A cheap ceramic or 2-xtal filter, about 15Khz bw would have been a nice addition to the K3, maybe even as a st'd component.
73, Barry N1EU Joe Subich, W4TV-3 wrote: > > >> Even with the 10 kHz channel spacing used in the USA, AM broadcast >> stations do not have 5 kHz audio bandwidth. The FCC requires a guard >> band between stations. As I recall, rgulations require that the audio >> start to drop off at about 4 kHz so that it can be down 20 dB >> or so by 6 kHz (the passband edge of the adjacent station). > > I don't think that's right ... or wasn't the last time I was around > an AM station (I spent most of my career in TV). I remember the AM > guys doing proof to 10 KHz. > > Admittedly, many of the directional stations could not maintain 10 KHz > through the phasors and the high end got trashed at night but the old > allocation systems generally kept first adjacent situations far enough > apart that 10 KHz could be obtained on groundwave during the daytime. > > "In the day" most receivers would start to roll off somewhere around > 6 KHz and the better ones had a 10 KHz notch for nighttime conditions. > > Given the DSP demodulation in the K3, it's a shame that there isn't > an "offset" option to do "vestigial sideband" demodulation (offset the > AM filter to the upper sideband or lower sideband) and demodulate > carrier and one sideband for better fidelity. This would work quite > well if the carrier were placed at the -6dB point on the composite > filter passband since it would keep the proper ratio between carrier > and sideband. Alternatively, the carrier could be moved to 1 KHz > from the -6 dB point and the DSP could equalize out the 6 dB boost > in audio below 1 KHz from the "opposite" sideband. > > 73, > > ... Joe, W4TV > > > > >> -----Original Message----- >> From: [EMAIL PROTECTED] >> [mailto:[EMAIL PROTECTED] On Behalf Of Alan Bloom >> Sent: Sunday, January 13, 2008 10:48 PM >> To: David Woolley >> Cc: [email protected] >> Subject: Re: [Elecraft] New K3 SN#207 built but question on AM Filter >> >> >> On Sun, 2008-01-13 at 02:49, David Woolley wrote: >> > Paul Webb wrote: >> > >> ... >> > The basic reason has already been explained, however, there >> are very few >> > cases were exceeding 3kHz audio bandwidth is useful. HF broadcast >> > stations use 5kHz channelling, which would only allow them >> 2.5kHz with >> > brick wall filtering at both transmit and receive ends, >> although they >> > probably do expect to suffer significant adjacent channel >> interference. >> > >> > MF broadcast stations use 9kHz channelling in Europe and >> 10kHz in the >> > USA, but I suspect that adjacent channel interference is less >> > acceptable. As they were designed to be received with LC >> IF filters, >> > with poor shape factors, I suspect they don't even make use >> of the full >> > channel, and if they did, they would probably be required to have >> > filters which put the adjacent channel into the filter stop band. >> >> Even with the 10 kHz channel spacing used in the USA, AM broadcast >> stations do not have 5 kHz audio bandwidth. The FCC requires a guard >> band between stations. As I recall, rgulations require that the audio >> start to drop off at about 4 kHz so that it can be down 20 dB >> or so by 6 >> kHz (the passband edge of the adjacent station). >> >> So there's not much point in the receiver audio being wider >> than 4 kHz. >> >> Al N1AL >> >> >> _______________________________________________ >> Elecraft mailing list >> Post to: [email protected] >> 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 >> >> > > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > 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 > > -- View this message in context: http://www.nabble.com/New-K3-SN-207-built-but-question-on-AM-Filter-tp14780362p14800931.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: [email protected] 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
