Lee,
The 300 hertz filter in the pegasus does not have a 1.5 to 1 shape factor.
If you tune in an S9+20 signal, you will find the filter is S9+14 or higher
over
a 300 hertz range. This is 300 hertz at the 6 db points. You will also
find
that the range for this signal being at least S2 (60 db points) is about
1200 hertz.
The rx340 specs also state the filters are all 1.5 to 1 or better shape
factor. The
big difference here is they really are. The same test above with the 100
hertz filter
in the rx340 yields 100 hertz between the 6 db points and 120 hertz between
the 60 db points for a real shape factor of 1.2 to 1. There is no need to
disable the AGC with this method.
The pegasus filters are adequate but the narrower filters do not meet their
specs.
Carl Moreschi N4PY
Franklinton, NC
----- Original Message -----
From: "WA3FIY" <wa3fiy@radioadv.com>
To: "John Peregord" <peregord@chartermi.net>; <tentec@contesting.com>
Sent: Tuesday, February 26, 2002 4:35 AM
Subject: Re: [TenTec] Re: Pegasus Filtering
> Hello John.
>
> If I understand correctly what you want to do, I don't believe it
> will work and in fact will render the Pegasus un-usable.
>
> The Pegasus is tuned in two different stages. Coarse tuning
> takes place in hardware at the front end of the radio. Coarse
> tuning happens in 2.5Khz steps. Fine tuning takes place in
> firmware in the IF DSP section AFTER THE 455 KHZ FILTER!
>
> The 455 Khz filter must have sufficient bandwidth to pass a
> signal plus it's sidebands that is moving across that bandwidth as
> you tune between 2.5Khz steps. If you reduce the bandwidth of
> the 455 Khz filter, under certain tuning conditions, the radio will
> clip desired sidebands and even worse, in certain cases,
> completely remove the desired signal. We users don't realize
> this is happening because software seamlessly takes care of all
> the details.
>
> I'm not sure about FM but in all other modes, the entire channel
> to channel selectivity is provided by the DSP. [I hate that
> expression "channel" but don't what else to call it. :-) ]
>
> I don't understand Carl's comment about the 300 hz filter
> having a shape factor of 1:4 or so. My Pegasus manual states on
> page V under "Receiver Selectivity" "...[filter bandwidths listed
> here] All 1.5:1 shape factor or better..." Because of the AGC
> action, this is not an easy parameter to measure so I can't
> confirm Ten Tec's specs. However, I find the selectivity
> adequate and the variety of bandwidth options outstanding!
>
> -73-
>
> -Lee-
>
>
> On 25 Feb 2002 at 19:41, John Peregord wrote:
>
> > Thanks to all that replied to my questions concerning the filtering in
> > the Pegasus. George brought up great questions that tell me I need to
> > do more homework. What the filters display at 300hz is exactly what
> > Carl explained (I just didn't know how to put into the right wording).
> > The Pegasus is working this way according to specs.
> >
> > I guess I'd like to try to get to do something it was not designed
> > for. I know the TS-870 and the Pegasus are different beasts but what
> > I'm suggestioning was done by Yuri, VE3BMV on the TS-870. Read his
> > section on this modification.
> >
> > Does anybody have or know where I could get my hands on schematics for
> > the Pegasus. My original Pegasus did not come with prints.
> >
> > Again, thanks to all for the education....I need to read and research
> > more about this stuff.
> >
> > John/KB8UMD
> >
> >
> > _______________________________________________
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> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
>
>
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