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[TenTec] Pegasus Filtering

To: <tentec@contesting.com>
Subject: [TenTec] Pegasus Filtering
From: n4py@earthlink.net (Carl Moreschi)
Date: Mon, 25 Feb 2002 03:44:27 -0000
The filters in the Pegasus are all implemented in DSP.
There is no way to improve the steepness of the skirts
without changing the pegasus firmware.  The 300 hertz
filter is 300 hertz wide at the 6 db points, but it is about
1200 hertz wide at the 60 db points.  It has about
a 4 to 1 shape factor.  This is similar to 500 hertz
crystal filters which hear over about 1200 hertz at
60 db.

If the DSP code were improved to make this filter
have steeper skirts, the propagation delay through
the filter would be too long for QSK operation.
I believe the speed of the DSP microprocessor
and constrants imposed on full QSK limit
the filter to its current value.

I find an outboard DSP unit such as the timewave 599zx
does wonders for improving the skirts of the filters.

Carl Moreschi N4PY
Franklinton, NC
----- Original Message -----
From: "George, W5YR" <w5yr@att.net>
To: "John Peregord" <peregord@chartermi.net>
Cc: <tentec@contesting.com>
Sent: Monday, February 25, 2002 2:18 AM
Subject: Re: [TenTec] Pegasus Filtering

> John, I was unaware that the Pegasus used any user-installable
> crystal filters in the 455 KHz IF chain. There is a fixed bandwidth
> or ceramic "roofing filter" there, but it is much wider than 300 Hz and
> changing it should have little or no effect upon the final IF bandpass in
> the DSP section.
> When you say that you measured the bandwidth of "my 300 Hz filter" is that
> measurement based upon the DSP filter selection of "300 Hz?"
> If the -6 db points of the 300 Hz DSP filter are such that the bandwidth
> 800-1000 Hz, then it sounds to me that something is drastically wrong with
> your radio.
> Sorry for any confusion, but this one has me stumped . . .
> 72/73/oo, George W5YR - the Yellow Rose of Texas
> Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
> Amateur Radio W5YR, in the 56th year and it just keeps getting better!
> QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
> Icom IC-756PRO #02121  Kachina #91900556  IC-765 #02437
> All outgoing email virus-checked by Norton Anti-Virus 2002
> John Peregord wrote:
> >
> > Has anybody experimented or attempted improving the IF filtering scheme
> > the Pegasus?  I was wondering if it would be possible to make a
> > similiar to what had been done to the TS-870 by some hams to improve
> > selectivity?  Could I substitute/modify the 455khz IF filter with
> > commericially available on the market.  My 300hz filter on the Pegasus
> > more like 800-1000hz....Is the Jupiter the same?
> >
> > This rig has been one of my best rigs considering the band for buck
> > I'd just like to tinker if at all possible since this list is always
full of
> > great ideas and information.
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