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(Fwd) Re: Transverters with *70cm* IF's



------- Forwarded Message Follows -------
From:          Self <Single-user mode>
To:            joseph v murray <k0vty@juno.com>
Subject:       Re: [amsat-bb] Transverters with *70cm* IF's
Reply-to:      davemetz@muscanet.com
Date:          Wed, 2 Feb 2000 08:44:10 -0600

 > To:            davemetz@muscanet.com
 > Date:          Wed, 2 Feb 2000 00:41:46 CST
 > Subject:       Re: [amsat-bb] Transverters with *70cm* IF's
 > From:          joseph v murray <k0vty@juno.com>

 > Hi Dave
 > 
 > One thing I can say is that you and I have the same rigs to contend with
 > grin.    I don't use the 28 mHz mix you speak of .      I have a pair of
 > 22c's and a pair of 40cx's plus a 2 ft dish on mode "S" .     Have worked
 > many with the unit.   

I've got a 20" dish with a G3RUH feed.  Its never been on the air :-(.

   I also have a 54 inch dish that I'd like to have
 > a dual helix feed for 1.2 and 5.6 gHz uplink for P3D .    All of my
 > desire has not been put to final design by a long shot.

I suspect that 5.6Ghz will be a long time coming.  I am sure that someone will
come up with a very small antenna for that band.  Maybe even a phased
array type FLAT antenna.  There is a huge need for that type of antenna for
those of us that live in areas with antenna zoning restrictions.  
There are a lot of us that need something that can be mounted flat on the roof.
I wonder if anyone is working on that problem?

     However it is
 > about  time that we as a community decide what is a good design .     
 > There has been considerable discussion about this ( some of it on the BB
 > and some not on the BB )     Hopefully all of this will come out in the
 > wash .       Do you know if anyone has done anything using 220 for a IF
 > with any success?     I don't see many 220 all mode rigs floating around.

This is true, 222 is still a pretty rare band.  I just completed a 222Mhz
transverter.  Like all of my VHF/UHF transverters, it uses a 28Mhz IF.

So that rules it out of the race forp uconversion service.  I could use it
as an IF for the 2.4Ghz receive converter though.
 > 
 > I have and use the DEM mode "S " down converter plus their preamp.   
 > Many years ago I had the converter made with two oscillators ( relay
 > switched  ) and 5 minute heaters attached to the xtals to shorten up the
 > drift time when turned on .    There was always more doppler drift to
 > contend with than xtal drift on Mode "s" at my qth.    My converter is
 > mounted at the dish and the preamp at the focal point of the dish.
 >
I only experimented with mine for a short time.  I saw that it badly needed
a crystal oven right off the bat.  And like all LO's using a Butler oscillator
circuit, the frequency was way off.  Too far off for my taste.  My dream LO
has the crystal in an oven and has a crystal that can be correlated.
  
 > Were you running digital up link and computer controlled doppler freq
 > changing that gave you the drift problem?

No, it was simple thermal drift.  My unit also used the "Russian" transistors
in it that DEM was in love with for a while.  Another correspondant has told me
that changing those back to 2N5179's reduced the drift considerably.
 > 
 > that noise figure meter sounds interesting.
 >
I have great hopes for it.   The design, schematics, etc for it can be found at

  http://escriba.cfn.ist.utl.pt/cupido/

It is used with a HP spectrum analyzer.  The nice part is that it works on any
frequency the analyzer covers.  In other words, you can measure the NF/gain
of a say 70cm converter at any IF frequency.   Calibration depends on the
calibration of your noise source.  That I can do at the next microwave conference.

  
 > Take care
 > 
 > Joe   K0VTY
 > 
--73-- David WA0AUQ

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