Joe, Good observations, all. I agree that 4.2 KHz is certainly good enough for communications audio.
The only reason I had for putting the FM filter in the 2nd receiver was to be able to hear more of the split in a broad pileup situation (like the extremely large split widths that we saw a few months ago with 7O6T), figuring that being able to simultaneously hear the wider bandwidth and see it on the P3 would be a great combination. I'll just have to be a bit quicker with the VFO-B knob ;-) 73, Dale WA8SRA On 9/26/2012 8:10 PM, Joe Subich, W4TV wrote: > The limit occurs several places ... adjust the "HI" setting and one > will find 4.20 is the maximum available. There is also an analog > lowpass filter in the audio (headphone and speaker) between the DAC > and the headphone/speaker amplifiers. > > I'm sure this limitation derives from the roughly 10 KHz clock/sample > rate used for the DAC ... Nyquist says the maximum frequency can not > be more than half the sample (clock) rate. 4.2 KHz is plenty good > enough for communications audio ... and not bad for AM with fading, > noise, and interference typical of medium and high frequencies. > > The FM filter still provides noticeably better double sideband AM > response (4.2 - 4.5 KHz with DSP/LPF skirts) than the AM filter > (3.0-3.3 KHz depending on the IF filter response). > > 73, > > ... Joe, W4TV > > > On 9/26/2012 7:23 PM, Don Wilhelm wrote: >> Sorry, but yes, the K3 audio is limited at 4 kHz, no matter whether it >> is to the headphones or to the speaker. Please do not "shoot the >> messenger". but that information is in the archives of this reflector in >> several places - it has been discussed periodically. >> >> If you want to lobby for extended audio response, that is fine, but I am >> just saying what the limits are today. Whether those can be extended or >> not is for the DSP designer to answer. >> >> 73, >> Don W3FPR >> >> On 9/26/2012 7:11 PM, Dale Boresz wrote: >>> On 9/26/2012 1:35 PM, Edward R Cole wrote: >>>> ... But I learned that audio is limited to 4-KHz >>>> regardless of IF filter so I ended up selling the extra 13-KHz filter. >>>> >>>> ... >>>> >>>> 73, Ed - KL7UW >>> I really hope that this does not apply to received audio to the >>> headphones or loudspeaker! I just purchased two FM filters (one for >>> sub-receiver to monitor wide splits) specifically to open up the receive >>> passband (audio included) for SWL and BCB reception. I have no intention >>> of actually transmitting FM or AM for that matter -- just want the wider >>> audio bandwidth for receive. >>> >>> So... is the received audio bandwidth *really* limited to 4 KHz? >>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
