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

[Don Wilhelm]

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.
>>     
>