Don I understand the demodulation theory just fine but the concept of having the DSP act as an audio filter instead of an IF filter causes some confusion since we've been hyping up "IF-DSP" filtering for several years now and suddenly we talk about AF-DSP in only one mode, AM. Maybe if the BW display showed 10 Khz instead of 5 Khz it would limit the confusion since that seems to be what most of us are used to. We understand that we only hear one of the two sidebands anyway. Oh well,,, I guess the question will keep coming up. Steve Ellington n...@carolina.rr.com ----- Original Message ----- From: "Don Wilhelm" <w3...@embarqmail.com> To: "Steve Ellington" <n...@carolina.rr.com> Cc: <n4z...@yahoo.com>; <elecraft@mailman.qth.net> Sent: Sunday, May 03, 2009 3:39 PM Subject: Re: [Elecraft] Shortwave filters for K3
> Steve, > > The DSP audio bandwidth *can* be moved out to 5 kHz for AM - that is true, > and it does not depend on the filter you have installed. > With the 6kHz filter at the IF, the bandwidth is constrained by the 6 kHz > roofing filter, so the realizable audio that can be demodulated is 3 kHz - > it makes no difference if the DSP opens the audio width up to 5 kHz, the 6 > kHz filter still restricts the audio to 3 kHz. > Now, install the 12 kHz roofing filter and the full 5 kHz audio width > allowed by the DSP can be realized. > > Study AM modulation for a bit and you should realize that the RF (and IF) > must pass both sidebands, but the demodulated audio will be only half the > width of the RF waveform. The available audio high frequencies can be > constrained by either restricting the RF (or IF) passband or by > restricting the audio bandwidth - either one produces the same result. > > With your "old shortwave receiver" controlling the IF at 6 kHz (3 kHz of > audio) when it begins to sound muffled? I would think so because most of > the filtering is done at the IF frequency. Equate that IF width to the > roofing filter width and the DSP bandwidth to the audio bandpass and you > will be correct. > > 73, > Don W3FPR > > > Steve Ellington wrote: >> Don >> This doesn't quiet make sense to me. I have the 6khz filter in my K3. The >> BW indicated on the K3 is 5Khz. If I add the 12 KHZ filter and the K3 >> still says 5KHZ and that 5KHZ is the "audio" bandwidth, what good have I >> done? Most any old SW receiver sounds a bit muffled at only 6khz >> bandwidth. Opening them out to 10 or even 15 KHZ always makes them sound >> better. Yes I know the BCB stations are limited to 5 Khz but just compare >> the K3 to a wideband rx and note the difference. >> Steve Ellington >> n...@carolina.rr.com >> ----- Original Message ----- >> From: "Don Wilhelm" <w3...@embarqmail.com> >> To: <n4z...@yahoo.com> >> Cc: <elecraft@mailman.qth.net> >> Sent: Sunday, May 03, 2009 2:01 PM >> Subject: Re: [Elecraft] Shortwave filters for K3 >> >> >> >>> Bill, >>> >>> The 5 kHz width indicated for AM is the *audio* bandwidth, not the IF. >>> The IF bandwidth must be more than 2 times the audio bandwidth for an AM >>> signal - so your 12 kHz filter is good. >>> >>> Remember that the 6 kHz filter must be used for AM transmit. >>> >>> AFAIK, most broadcast stations limit their transmitted audio to 5 kHz, >>> so you are not likely to obtain much better fidelity than the K3 DSP >>> currently allows. >>> >>> 73, >>> Don W3FPR >>> >>> Bill Maddock wrote: >>> >>>> Guys, >>>> >>>> Just got done assembling my second K3 and this one has a 13 Khz >>>> filter where #1 had 6 Khz - I like to do shortwave listening - thought >>>> the wider filter would give better fidelity, but DSP only goes >>>> 5Khz wide is there a mode for this? I assumed with the 13khz roofer >>>> it would be opened up to 10 khz or more? >>>> >>>> Thanks and 73, >>>> >>>> Bill N4ZI K3 #1059 & K3 #2914 >>>> >>>> >>>> >>> ______________________________________________________________ >>> 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 >> ------------------------------------------------------------------------ >> >> >> No virus found in this incoming message. >> Checked by AVG - www.avg.com Version: 8.5.325 / Virus Database: >> 270.12.15/2093 - Release Date: 05/02/09 14:23:00 >> >> ______________________________________________________________ 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
