[Elecraft] Crystal Filter Offset in 4.81, What does it mean?

[Brian Alsop]

I should also point out that his shows no measurable effect on the 250 
and 200 Hz filters. 400Hz and wider are impacted.

On 2/5/2014 14:37, Brian Alsop wrote:
> Guys,
>
> I ran a sweep of the filter response with a 400 Hz filter at nominal 0.2
> and 03.
>
> I have the plot but can't post here.
>
> In short the left side of the filter response is moved to the right. The
> right side moves slightly inward as well.
>
> The net effect is a narrowing of the filter -6db bandwidth and also a
> small shift in center frequency.
>
> Here are the numbers:
>
> BW (-6dB) =380 Hz, center 485 Hz @ 0.2
> BW (-6db) =300 Hz, center 508 Hz @ 0.3
>
> It appears if you do this, you might also have to adjust the filter
> offset to bring the center of the passband back to the nominal pitch value.
>
> 73 de Brian/K3KO
>
> On 2/5/2014 13:40, Mike K2MK wrote:
>> I installed the 4.81 beta firmware and I am able to change the crystal
>> filter
>> offset as described in the firmware notes. I can hear slight
>> differences in
>> a CW signal between 0.1, 0.2, and 0.3 KHz. What I don't understand is
>> what
>> does it mean. Previous to this release I would have assumed that the
>> crystal
>> filter is centered on my chosen CW pitch suggesting a 0 KHz offset. If I
>> choose one of the 3 offsets am I now listening (and transmitting)
>> slightly
>> off zero beat. Why would I want this? Wouldn't I also want a 4th
>> choice of 0
>> KHz?
>>
>> Explanations in layman's terms would be appreciated.
>>
>> 73,
>> Mike K2MK
>>
>>
>>
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Checked by AVG - www.avg.com
Version: 2012.0.2247 / Virus Database: 3684/6563 - Release Date: 02/05/14