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Re: 1296 Transverter design advice

> Date:          Thu, 25 Feb 1999 07:51:25 -0500
> From:          "CAPT J. A. Sanford" <reactor@roosevelt.navy.mil>
> Organization:  Reactor Department
> To:            davemetz@muscanet.com
> Subject:       Re: [amsat-bb] 1296 Transverter design advice

> Dave:
> some thoughts from a guy who's thought about this a long time, but not
> yet built anything.
> There are a multitude of VCO's available cheap.  Use one of them for the
> LO, pick one with the lowest phase noise.  Almost all have output in the
> +7dbm range, so easy to drive a dbm.  Synthesize the LO with one of the
> cheap motorola (& other) PLL chips.  This is a new design, but not too
> hard with currently available hardware.

I've gone a long way down this road for another project.  The brick wall
I ran into was getting the software written for the microcontroller.  I'm not
a software man so I tried depending on others in our club.  The result
is two years have gone by (three programers later) and no software.
Yup, I even got a Motorola development kit, the VCO's, the whole
nine yards.  Unless you can personally write the code. Forget about
the PLL VCO approach.  
> For frequency reference, I bought a highly accurate TCXO from Rakon (10
> MHz) that I intend to use as reference for all my microwave stuff.
Excellent idea.  What did it cost?  I have a highly accurate 1Mhz standard
in my service monitor that I could use.
> You'll need a good diplexer downstream of the dbm, not hard to do with
> 400 mhz IF.

This brings up another good point.  In some designs I see a diplexer,
in others not.  I used one in my two meter receiving converter but did not
in the 222Mhz rig.  Its mixer is terminated by a ERA-1 MMIC.   How 
important is the diplexer?
> Hardest part is bandpass filtering at RF.  This is important to keep out
> other signals, particularly image frequency.  You choice of 400 mhz IF
> simplifies this, at the risk of giving you a problem if p3d is in mode
> L-U.
Another good point.  I hope to be able to use my two meter receiving
setup as the IF for the 2.4Ghz downconverter.  This would leave the
70cm rig free for the up link.
> Post diplexer gain is easy with the mmic's available, but again some
> bandpass filtering is a good idea.  (here's where the no-tune stuff
> shines . .)

Speaking of filters.  I like the interdigital ones that were in the 
last issue of QEX.  They look like a good solution.  I'm using helical resonators
in the 222Mhz rig.  Trust me, they work great but are a real pain to build.
Next time I'll look closer at the mechanical considerations before
picking a filter design.
> For RF amp:  The modules which are available from RFParts (among others)
> are a good choice.  mw in to 3 watts (or so) out, and 1.5 watts in to 18
> watts (or so) out.  You have some excess drive here, so if you can come
> up with a good splitter, the 3 watt device can drive a pair of the 18
> watt modules for a fairly powerful signal.

I've used the hybrid modules in my 6M and 222Mhz transverters and they
have done a great job.  On 1.2Ghz cost is a consideration.  I can use the 
10mW to 1.5 mW module as a driver, true.  But then the cost to get to
18 watts is about $180.   Maybe that's not too much :-) at this frequency.
On the VHF rigs I use a discree component "MMIC" designed by Zack
at the ARRL labs for a driver stage.  It gives me 100mW (up to 70cm)
from a MAV-11 MMIC driver.   What we need is something like that
running class AB to eliminate that costly first hybrid.
> For L-band up to p3d, I intend to use a single module at 18 watts,
> providing the rest of the ERP with antenna gain.  For my terrestrial
> system, I intend to drive a pair, to give me enough signal to help
> generate some activity.

Again, I was thinking along simular lines.  Except mounting the P.A.
at the antenna to beat the feedline losses.  
> Hope this helps . . . anxious to hear what you decide and see your
> results if you get to the hardware before I do.
You will, I am hoping to get a open discussion going on this problem.
Maybe stimulate some tech talk on the reflector.
> 73, Jim
> wb4gcs@amsat.org
> Dave Metz wrote:
> > Dear Group,
> >
> > I'm planning to build a transverter for 1296 as my next project and
> > am looking for your recomendations on the design.  I'd like to
> > do something other  then the "no tune" kit.  Its more fun that way.
> >
> > This transverter would be for SSB weak signal work.  A lot of
> > its time would be for "L" band uplink service on P3D when it
> > flys.  In other words, I'm looking for a few watts of output.
> >
> > Any comments, sage advice, and design recomendations
> > (such as for the  L.O. pre-amp,filters and P.A.) would be
> > appreaciated.
> >
> > I'm currently considering used my TR-851A 70cm rig as the I.F.
> > This would free up my two meter system for use as the receiving
> > I.F. for another microwave band.
> >
> > --73-- David WA0AUQ
> >
> > davemetz@muscanet.com
> > ----
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