[RTTY] RTTY spectrum analysis article

[Joe Subich, W4TV]

Phil,

Using the "soft" option instead of the hardest (steepest) may help
with regard to the narrow bandwidths as the softer skirts/more gentle
change from passband to stopband should result in lower inter symbol
interference.  I contend the increased ISI due to group delay is a
significant disadvantage of narrow filters - particularly with sharp
skirted DSP applications.

DSP filters tend to have *much* steeper skirts than a crystal filter
of the same passband width.

73,

    ... Joe, W4TV


On 1/10/2013 12:41 PM,  pcooper wrote:
> Hi all,
>
> I must have missed the original posting about this subject, but just wanted to the thoughts from Bill W6WRT with respect to the new Icom rigs.
>
> Bill wrote:
> "Interesting. For years I used 250 Hz filtering in my IC-765Pro3, so
> when I got my new IC-7600 I set it the same way. The reception seemed
> pretty poor, so on a hunch I widened it out to 300 Hz and things
> returned to normal. Not sure whether the actual bandwidth was
> different or if the skirts on the '7600 were too steep. Anyway, 300
> works fine."
>
> I purchased a new IC7800 in 2011 to replace the trusty old IC756Pro.
> On getting it, I set everything in the 7800 as I had it in the Pro.
> The tight filter (for contesting) was set to 250Hz, which worked very well for me. I also had a 450Hz filter for when I was in S&P mode.
>
> However, my first session with the 7800 on RTTY turned out to be less than I expected.
> I was having problems decoding even strong RTTY signals, so I played around with the filter settings, and found that I had to use a 400Hz filter as the tightest setting, with the next one being 600Hz for S&P.
>
> I also had to set the roofing filter to 15kHz, as the 6kHz and 3kHz filters were just too limiting.
>
> Maybe the DSP side of things has changed more than I expected in the Icom rigs of late!
>
> 73 de Phil GU0SUP
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