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[TenTec] Re: RX-340 and Noise Reduction

To: <tentec@contesting.com>
Subject: [TenTec] Re: RX-340 and Noise Reduction
From: Jim FitzSimons" <cherry@getnet.net (Jim FitzSimons)
Date: Sun, 17 Feb 2002 20:46:58 -0700
Ten Tec provides complete diagrams and schematics of the Pegasus.
I have them. I also have the manual for the RX-330.

----- Original Message -----
From: "Jim Reid" <jimr.reid@verizon.net>
To: "Carl Moreschi" <n4py@earthlink.net>; "tentec" <tentec@contesting.com>
Cc: <kh7t@arrl.net>
Sent: Sunday, February 17, 2002 14:30 PM
Subject: Re: [TenTec] Re: RX-340 and Noise Reduction

> Hi,
> Yesterday I wrote:
> "I suspect the Orion will similarly have a rich set of DSP filters.
> And probably nary a crystal filter."
> Wrong!  John Buck,  KH7T pointed out that the 1st IF of both
> the Pegasus and the RX-340 is at 45.455 mHz.  Something
> has to be done to eliminate the "birdies"  which would be
> generated by the 1st mixer spurious products and the 2nd
> mixer image at 910 kHz offset.  So I went looking in the
> 340 manual again.  Sure enough, there are two crystal
> filters: a pair of 2 pole crystal filters do the job in the 340,
> and probably also in the Pegasus. (Note: the Pegasus
> manual is completely unlike any previous Ten Tec
> radio manual I have had -- absolutely NO  circuit
> details,  diagrams, etc.  at all!? Wonder why.  The 340
> manual is chock full of details: pc card layouts,  alignment
> and elaborate test instructions,  but nary a word about
> any of it in the Pegasus book.  Is there a separate
> Pegasus Service Book available??).  I probably wouldn't
> touch a thing anyway;  don't like surface mount component
> fiddling,  hi.
> Therefore,  I suspect the Orion will also have a 45.455 mHz
> IF (note the 455 part which is the 2nd IF frequency),  and
> will have the same needed pair of crystal filters,  one on
> the input,  the other on the output of some gain stages within
> the 455 kHz IF strip.  These filters are 16 kHz wide in the 340;
> may be only 8 kHz in the Pegasus.
> The "main" rcvr within the Orion is said to be only amateur
> bands,  so it probably only needs to be 8 kHz wide;  however,
> the "sub" or dual rcvr of he Orion will be general coverage,
> wonder if that one might have a wider IF,  as in the 340 for
> more "hi-fi" international broadcast reception, synchronized
> AM?
> Will sure be interesting to see what comes within the Orion,
> won't it?
> A bit more, also from KH7T which might explain the high gain
> within these DSP core rigs.  A quote from one of John's posts
> to me (trust he doesn't mind my giving it out,  hi):
> "My limited DSP work would suggest that the gain of the amplifiers will
> be adjusted to keep the DSP digital sample memories as near full scale
> as you can without any overflow.  Therefore the gain will be greatly
> increased when there are no strong signals in the passband.  So you have
> to manually limit the gain to prevent the effect that we have been
> discussing.  That is ok because you cannot use stuff below the noise
> Now if you were using additional DSP to dig out correlated stuff below
> the noise level then you might use more gain and your receiver[the 340]
> would be  superb for this purpose.  Note Ed Hare's comments in
> QRP-L about trying  for dsp enhanced 10 micro watt trans continental
> work.
> John KH7T"
> And that high noise when " the gain will be greatly
> increased when there are no strong signals in the passband.
> So you have  to manually limit the gain to prevent the effect that
> we have been  discussing."
> My experience as noted in previous posts exactly!  So turn
> down the RF gain of your Pegasus/RX-340,  you won't miss
> a signal so long as you can still just here the antenna noise
> contribution when switching the antenna ON/OFF as you
> cut the gain.  Found I was cutting the gain of the IF strip
> by 65 dB last evening on 40 meters.  Result was a nearly  dead
> quiet rcvr,  but signals just appeared from the speaker when
> tuned across,  very interesting effect.
> 73,  Jim  KH7M

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