> Please do not be confused. The DSP *is* at the IF frequency, *and it
> does* process AM at the full bandwidth for all modes as required.
That is only true to the extent allowed by the roofing filter. Thus
if one has the 6 KHz AM filter and is tuned EXACTLY to the carrier
of the AM station, the audio bandwidth is something around 3300 -
3500 Hz because the Roofing filter will be down 6 dB at +/- 3 KHz.
One can get a full 5 KHz (really 4.2 KHz since that's the maximum
audio frequency supported by the DSP) by tuning slightly to one
side of the carrier to receive one full sideband.
> (FM might be different, I don't have the FM filter to try).
FM displays N/A ... the DSP is "fixed" at the 15 KHz IF/4.2KHz AF.
> > 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.
When the DSP showed the IF bandwidth in AM and the audio bandwidth
in other modes if caused far more confusion than it does now. In
addition, it broke all of the software width controls because of
the inconsistency when changing modes.
> Please believe me. I'm not confused. It just needs to be made clear to
> people who purchase the 13 Khz filter will only see 5 Khz on the
> display.
5 KHz is fiction anyway since the DSP has a high cut of 4.2 KHz
(2.8 KHz in CW). BW may say 5.00 but the real bandwidth is only
4100 Hz (100 to 4200 Hz). Audio response is down 60 dB or more
at 4.5 KHz even when BW says 5.00.
73,
... Joe, W4TV
> -----Original Message-----
> From: elecraft-boun...@mailman.qth.net
> [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Don Wilhelm
> Sent: Sunday, May 03, 2009 5:03 PM
> To: Steve Ellington
> Cc: elecraft@mailman.qth.net
> Subject: Re: [Elecraft] Shortwave filters for K3
>
>
> Steve,
>
> Please do not be confused. The DSP *is* at the IF frequency, *and it
> does* process AM at the full bandwidth for all modes as required.
>
> The AM bandwidth *used to be* displayed as the IF bandwidth, but many
> were confused because it was double the bandwidth that could be heard
> - so it was changed to *display* the audio bandwidth.
> It is a matter of display only, and not the actual operating IF width.
>
> The display of the audio bandwidth in AM is consistent with the
> bandwidth displayed for other modes - the audio bandwidth is what is
> displayed. (FM might be different, I don't have the FM filter to
> try).
> In any case, now the DSP displayed bandwidth is equal to the audio
> bandwidth, no matter what the actual IF processing width may be.
>
> 73,
> Don W3FPR
>
> Steve Ellington wrote:
> > 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
> >
> >
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