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
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!
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.
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