Ron: I agree with you that, unlike a typical analog receiver and product detector demodulating either the upper or lower sideband of a full-carrier AM signal at zero-beat, I found the K3's audio to be exceptionally clean. So clean, in fact, it sounds like an analog synchronous detector even though you might actually be off frequency a couple of Hz from zero beat. I believe the reason for this is due to the extremely low intermodulation distortion inherent in a DSP-based demodulator.
Last week when I was testing the K3 SSB modulator for IMD using the conventional 2-tone approach, I noted that while the 3rd and 5th-order IMD products were at levels comparable to a well-designed analog radio (primarily due to LPA and HPA non-linearity effects), the higher-order IMD is almost non-existent. When the K3's IMD output spectrum is compared to some very well-regarded analog radios, there's no comparison, in that all the analog radios generate some IMD "grass" on the spectrum analyzer that just doesn't appear on the K3. I would be willing to bet the same effect takes place on the receive side as well. Scott N7NB -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ron D'Eau Claire Sent: Sunday, February 17, 2008 10:49 AM To: 'Björn Mohr'; elecraft@mailman.qth.net Subject: RE: [Elecraft] K3 AM vs FM filter For what it's worth, I'm rather astonished by the audio quality of the K3 when receiving AM in "SSB" mode. No typical "SSB sound" at all, and the tuning allows getting on frequency within a couple of Hz, in the worst case, so audio frequencies are very accurately reproduced. Using an external speaker, I've switched between the K3 with the 6 kHz filter in SSB mode and another good-quality conventional AM receiver and neither I or visitors can tell whether we're listening to the K3 in SSB mode or the AM receiver, listening to either music or voice. I set up my K3 doing Ref Cal using procedure 2 in CW mode, so I can hear that I've got the K3 tuning calibrated within a Hz or less. Then it's only a matter of dialing up (or doing direct frequency entry) for the station I want to be perfectly tuned in. Ron AC7AC -----Original Message----- Hi Bjorn, The 6 kHz filter "is" required for AM Transmit. The FM filter will not work. The FM filter will work on RX, but will not be as good with image rejection as the 6 kHz filter. I would suggest starting with just the 6 kHz filter. Then if you feel like you want/need the FM filter for AM receive, go for it. 73 Greg AB7R -----Original Message----- Hi gang, As I understand it the FM filter would be best for AM BC with its wider bandwidth. Not perfect, but certainly better than the "AM filter" that I guess is aimed towards voice AM communications. Has anyone tested the FM filter for AM broadcast reception? If so, what is your comments and advice? Is it suitable for this purpose, or are there a better solutions out there. Regarding AM voice operation, I do one AM contest per year. I guess it would be possible to use the FM filter also for AM TX and restrict the bandwidth on a DSP/audio level, or is this a bad idea? 73 de Björn /SM0MDG _______________________________________________ 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 _______________________________________________ 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
