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

Wed Jan 7 21:49:08 EST 2009

Thomas,

I believe you are mis-interpreting my response.  It is not a limitation 
of the K3 that I am concerned about.  I just believe that it is 
"adverturesome" to run with an extremely wide bandwidth 'just because it 
is possible'.  I prefer to use a narrow bandwidth because it avoids a 
lot of potential problems such as overload of the system at several 
places - mainly the ADC portions.

Yes, that should be your choice, up to the bandwidth that the radio 
provides.  If you can convince the folks at Aptos to increase the 
available bandwidth for data modes, that is all well and good.  I for 
one would not advocate that message because it has great potential to 
increase the customer support "issues" that would occur when more naive 
operators experience overload conditions or severe AGC pumping.

If you wish to operate digital modes in ESSB mode, the K3 provides that 
capability - it is just not present in the current digital mode set of 
options.

So you *do* have your choice, but not in the set of digital modes 
recommended for the K3.

73,
Don W3FPR

Thomas Bingenheimer wrote:
> 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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