[RTTY] RTTY Rx filter bandwidth

[Joe Subich, W4TV]

On 1/10/2013 2:01 PM, Ed Muns wrote:
 > The KFLA-250 is nominally 370 Hz wide at the -6 dB points.

Which is why it makes little sense to put both the KFL3A-400 and
KFL3A-250 in the same K3<G>.  Again, see the Elecraft filter plots:
    http://www.elecraft.com/K3/K3_filter_plots.htm

370Hz is very close to the theoretical limit - one can debate whether
the 3rd, 5th or 7th harmonic of the 22.727 Hz "clock" are required to 
adequately reproduce the edges of the keying waveshape - for minimum
ISI.  The 400 Hz filter provides just a bit more ease of tuning at
minimal added risk of close in AGC effects and 400/200 is a better
combination that 500/250 on CW.

73,

    ... Joe, W4TV


On 1/10/2013 2:01 PM, Ed Muns wrote:
> The KFLA-250 is nominally 370 Hz wide at the -6 dB points.
>
> If SHIFT is needed to center the filter on the Mark/Space signals, then the
> filter needs an offset in the CONFIG parameter.  Despite the claim that the
> 8-pole filters have zero offset, I've found a number that do.  This is
> especially important on these narrow bandwidth filters.
>
> Ed W0YK
>
> Dave K6LL wrote:
>> I use the 250 Hz roofing filter and DSP BW 350 as my go-to
>> RTTY settings on the K3.  It seems to work well for me.  Use
>> the SHIFT control to make sure the mark and space are
>> centrally spaced in the spectrum display.  The mark and space
>> should be just about the same amplitude as the center
>> amplitude, with the sidebands tailing off on both sides from there.
>
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