[Elecraft] K3 Filters for digital work

[Joe Subich, W4TV]

 > My K3 copies RTTY fine through the 200 Hz filter.

This is much like the old ads "I worked 150 countries with my
Gotham vertical" ...  When one tries to pass a FSK signal through
a "too narrow" filter it doesn't just stop working.  However, the
tight skirts of the filter cause the energy in the mark and space
channels to smear (pulse stretching) into the next bit period and
cause errors in decoding.

If one is trying to copy a strong, stable signal in the presence
of strong adjacent channel interference, the "too narrow" filter
may provide improved copy by reducing AGC capture from the QRM.
However, if one is trying to copy a weak signal with flutter or
selective fading in flat noise, copy will be much worse with the
"too narrow" filter.

Chen, W7AY has written a lot on FSK decoding.  I strongly recommend
his web site (and following some of the bibliography) for understanding
RTTY, required bandwidth and filters.

73,

    ... Joe, W4TV


On 11/29/2013 9:04 AM, Bill Breeden wrote:
> Dave,
>
> I have 200 Hz and 400 Hz filters in my K3.  My K3 copies RTTY fine
> through the 200 Hz filter.  That being said, I normally use the 400 Hz
> filter unless the band is crammed with signals during a contest.  The
> 200 Hz filter also reduces a the apparent signal to noise ratio between
> my ears when working CW on the low bands during very noisy conditions.
>
> 73,
>
> Bill - NA5DX
>
>
>> Which two of the 200/250/400 and 500 hz filters are best for digital
>> use, primarily RTTY, both contests and dx.  I understand that for JT-65
>> and PSK the standard ssb filter, or even the AM filter is useable.  I am
>> concerned that the 200 hz might be too narrow for RTTY.  I work some CW
>> but almost no ssb.
>
>> 73, Dave, K2YG
>
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