Jay, Ekki, and all,
I suspect you are both correct but I would also like to consult with the
signal processing experts on the math. Ekki, can you steer me to some math
sources on your BW calculations?
I am also using the IC 756PRO as Ekki is and have to make sure my narrowest
settings in crowded conditions are a little wider. I settled on 300 Hz as I
found 250 Hz too narrow. This was just by experimenting.
But, Jay, this is a DSP filter inside the AGC loop with "brick wall" sides.
I also was OK with my IC 765 with its 250 Hz "standard shape" filter.
Again, as Ekki noted, this was with weaker signals in crowded conditions
that I was OK with the narrow filter on the 765 but not OK with the 756PRO.
I did a "shape test" with Brian Beezley's RITTY display and found both radio
filters to be very accurate in both bandwidth and center frequency. But, of
course, the skirts on the DSP filter were as vertical on the display as I
could visually detect. (about 30 db or so). The audio actually drops off
like a stone.
So I am now interested in the math to see if there is some correlation I
could match up. Ekki's analysis is the first I have seen on "practical"
bandwidth calculation.
Any other "wizards" out there ?? (Chen...)
73, George .. W1ZT
----- Original Message -----
From: "Jay" <jay@ieway.com>
To: "Ekki" <ekki@plicht.de>; "_Rtty" <rtty@contesting.com>
Sent: Tuesday, August 28, 2001 4:59 PM
Subject: RE: [RTTY] Bandwidth of a RTTY signal (was:SO2R RTTY Radio)
> At 10:17 PM 8/28/01 +0200, Ekki wrote:
> >> If possible, use a 250 Hz filter for RTTY. 500 Hz is ok for Pactor but
> >> unnecessarily wide for RTTY.
> >
> >I beg to differ :-)
>
> Well I beg to differ )!
>
> I have used 250 Hz filters in my final IF for RTTY operation since 1985 or
> so in contests. I have used them with Icom 751, Icom 761, Icom 765,
Kenwood
> 850, Yaesu FT-1000, Icom 706, Kenwood 940, Kenwood 930, Yaesu 990. All
> stock manuf. filters.
>
> All stock manufacturer filters at 250 Hz in no way, shape, or form
actually
> pass only 250 Hz you need to note that most are 250 Hz at 6 Db.
>
> Actually use what ever you like. But here's what others have said about
> this subject:
>
> Walter, DL4RCK - I am running a TS850SAT and it work very well with RTTY
> with a 500Hz and 270Hz filter.
>
> Bruce, WT4I - Used on FSK, 250 and 500 Hz filters
>
> Roy, N8YYS - Have 500 Hz and 250 Hz IF filters (INRAD).
>
> Jan, SM5FUG - Filter: 270 Hz (in 8.83 MHz IF) and 500 Hz (in 455 kHz IF).
>
> Don, AA5AU - I use either the 500 hz or 250 hz filters.
>
> Hal, WA7EGA 250 Hz lets me operate in a crowded band.
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