[Elecraft] Mildly confused - Assumed filter width and what I see in waterfall do not match

[Thomas Bingenheimer]

I guess my basic answer, is that should be my choice, not the radio firmware. If I want to run 4 (or say, 10khz) into my computer (and out) that should be my choice. After all, how is an SDR all that different. Again, I suspect this is a oversight in the firmware, not a design choice. Why should such a flexible radio be hobbled in this manner? (assuming, of course, that it is actually limited as such, as opposed to me setting it up wrong :) ).


--- On Wed, 1/7/09, Bob Cunnings <bob.cunnings at gmail.com> wrote:

> From: Bob Cunnings <bob.cunnings at gmail.com>
> Subject: Re: [Elecraft] Mildly confused - Assumed filter width and what I see in waterfall do not match
> To: elecraft at mailman.qth.net
> Date: Wednesday, January 7, 2009, 8:59 PM
> Disabling the AGC in the K3 certainly does "do the
> trick" in terms of
> preventing strong signals in the passband from reducing
> receiver gain
> and thus affecting the weaker signal I'm decoding -
> that's exactly why
> I do it.
> 
> As for ADC overload -that's a risk I'm well aware
> of but most of the
> time it's a non-issue, for me at least. If it happened
> I would react
> to it, but I rarely encounter signals in the passband at
> anywhere near
> the level to cause trouble of that sort.
> 
> Bob NW8L
> 
> On Wed, Jan 7, 2009 at 6:23 PM, Don Wilhelm
> <w3fpr at embarqmail.com> wrote:
> > Bob,
> >
> > That will do the trick in an analog only receiver, but
> a receiver like the
> > K3 has an analog front end followed by an ADC and DSP
> processor.  The trick
> > is to keep from overloading the ADC - should that
> happen, the copy will be
> > garbage.
> >
> > That situation is not limited to the K3 - overload of
> the soundcard ADC is
> > also a possibility with equally bad results.
> >
> > I have to admit that in many cases, one can operate
> with a wide bandwidth
> > with no problem, but when that strong signal enters
> the passband, the wide
> > bandwidth possibilities are "all over".  I
> chose to take preventive measures
> > before that happens.
> >
> > 73,
> > Don W3FPR
> >
> > Bob Cunnings wrote:
> >>
> >> I simply disable AGC when I wish to run a wide
> receive bandwith with
> >> PSK31 for "point and click" tuning -
> precisely to avoid such a
> >> problem.
> >>
> >> Bob NW8L
> >>
> >> On Wed, Jan 7, 2009 at 5:44 PM, Don Wilhelm
> <w3fpr at embarqmail.com> wrote:
> >>
> >>>
> >>> Thomas,
> >>>
> >>> I will not answer your questions directly,
> >>> BUT
> >>>  From an operational standpoint, using a wide
> bandwidth for data modes
> >>> is *not* the best way to do it.
> >>> The reason is AGC in the radio.  Any signal in
> the receiver passband can
> >>> activate the AGC - and that is fine *if and
> only if* the strongest
> >>> station in the receiver passband is the one
> you are working - usually
> >>> that is not the case.   The strong signal will
> reduce the receiver gain
> >>> due to its AGC action and the station you are
> trying to QSO with will be
> >>> reduced along with it.  Overload of the DAC by
> the strong signals is
> >>> another similar consideration - fortunately,
> the K3 employs a hardware
> >>> AGC ahead of the DAC to avoid just that
> possibility.  The DSP ADC can
> >>> handle an S9+20 signal without overload, but
> there are signals stronger
> >>> than that even in the sub-bands commonly used
> for digital.
> >>>
> >>> Using a narrow passband for data modes allows
> one to avoid that
> >>> situation.  Yes, one must tune with the VFO to
> place the desired station
> >>> inside the receiver passband, but the
> possibility of a QRM free QSO is
> >>> much greater with the narrow passband.
> >>>
> >>> Just because the software application can
> display a 4 kHz slice of the
> >>> spectrum is not sufficient reason to use a
> wide receiver passband IMHO.
> >>>
> >>> Elecraft may well consider it just because
> some folks want to operate
> >>> that way, but it certainly does not make much
> sense to me.
> >>>
> >>
> >
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