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

[Brian Alsop]

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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