On 1 Apr 2002 at 18:57, George, W5YR wrote:
>[snip]
> However, and this is the other side of the coin, if one can hear a
> certain noise level with the antenna disconnected, then connecting the
> antenna must increase the noise level. If it does not, then the
> receiver has a problem with excessive internal noise AND/OR there is
> insufficient gain to bring the antenna noise up to a level that
> exceeds the internal noise level. In either case, the receiver
> performance is deficient.
> [snip]
First I agree with previous statements that the PJ's are very
quiet radios. When I first got my Pegasus, I thought for sure it
was deaf, just like me. :-) However, after using it and a
Jupiter I subsequently obtained, I find I can hear anything I can
hear on any other RX I have available AND as George mentions
above, I can hear antenna noise well above the RX noise on any
band.
Why is it so quiet yet hears so well? Perhaps the answer to that
question is found in "Solid State Design for the Radio Amateur"
by Hayward and DeMaw and published by ARRL. In the section
on receiver design basics they identify the problem of
broadband noise in receivers where the selectivity is near the
front end and is followed by high gain i-f amplifiers. [See
previous discussions about the desirability of sharp front end
selectivity] After establishing the problem, they go on to say
"...The main need is to restrict the bandwidth of the noise
reaching the audio output. This means that additional selectivity
is required somewhere in the receiver............the ultimate solution
is to use proper i-f selectivity just preceding the product
detector...." [page 87 in my first edition]
Enter i-f DSP. With i-f DSP, significant selectivity is inserted
somewhere around the product detector. I don't know if it is
before or after. The PJ's at least, use the phasing method of
reception, so the selectivity could be inserted after the product
detection and just prior to D/A conversion to high level audio.
But whether it is before or after the product detector, there
will be almost no receiver noise outside the selected bandwidth.
Regardless of how or why the PJ's are so quiet, I find them to
be the most pleasant sounding communications receivers I have
ever listened to.
Just when I think it can't get any better, along comes the Orion
with narrow filters in the front end for maximum dynamic range
AND i-f DSP filters at the tail end to reduce noise and further
tighten selectivity. This has to be approaching perfect reception
capability.
-73-
-Lee-
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