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

[Thomas Bingenheimer]

I would like to at least get the 4.2 khz mentioned - but in fact, I do not. My chief concern is that I should at least be able to use the full 4 khz waterfall that I can, in fact, get out of most other radios.


--- On Wed, 1/7/09, Joe Subich, W4TV <lists at subich.com> wrote:

> From: Joe Subich, W4TV <lists at subich.com>
> Subject: RE: [Elecraft] Mildly confused - Assumed filter width and what Isee in waterfall do not match
> To: tpbx at yahoo.com, elecraft at mailman.qth.net, "'Bob Cunnings'" <bob.cunnings at gmail.com>
> Date: Wednesday, January 7, 2009, 10:15 PM
> > 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.
> 
> The K3 does not support an audio bandwidth higher than 4.2
> KHz 
> in ANY MODE.  If you do some checking you will find the
> DSP's 
> digital to analog converter effectively includes a 4.2 KHz 
> "brickwall" filter ... even in AM mode with the
> "bandwidth" 
> set to 5 KHz (10 KHz IF).  
> 
> If you expect audio response above 4.2 KHz, you will need
> to 
> convince Wayne and Lyle to relax the upper frequency limit.
> 
> HOWEVER, for digital modes I'm not so sure that is a
> good 
> idea.  With sound cards sampling at 11025 Hz, the input
> audio 
> needs to be band limited to 5.5 KHz maximum and 4.5 KHz
> offers 
> a fair margin for safety to handle the occasional
> application 
> that runs at 8 or 9 KHz.  
> 
> For AM - since the digital modes are not a consideration -
> it 
> would be nice to have 5.5 or 6.0 KHz response. 
> 
> 73, 
> 
>    ... Joe, W4TV 
>  
> 
> 
> > -----Original Message-----
> > From: elecraft-bounces at mailman.qth.net 
> > [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
> Thomas 
> > Bingenheimer
> > Sent: Wednesday, January 07, 2009 9:07 PM
> > To: elecraft at mailman.qth.net; Bob Cunnings
> > Subject: Re: [Elecraft] Mildly confused - Assumed
> filter 
> > width and what Isee in waterfall do not match
> > 
> > 
> > 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.
> > > >>>