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Re: MicroWave: 1296 Transverter design advice



> Date:          Fri, 26 Feb 1999 21:54:02 -0500
> To:            Dave Metz <davemetz@muscanet.com>
> From:          Doug McGarrett <dougmack@spacelab.net>
> Subject:       Re: MicroWave: 1296 Transverter design advice

> At 08:34 2/26/1999 -0800, you 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.
> > Any comments, sage advice, and design recomendations 
> > (such as for the  L.O. pre-amp,filters and P.A.) would be 
> >appreaciated.
>
> > --73-- David WA0AUQ
> >
> Why not use a phase locked oscillator for the LO?  Forget all that
> miserable multiplication.  What you will need to do, however, is
> come up with a VCO on the LO frequency.  You may be able to build it 
> from scratch using a ceramic resonator, you might be able to buy it 
> from Murata or Minicircuits, I don't know offhand who has what at that
> frequency.  I know you could get an 864 MHz vco from Murata for a 432 IF.

The Mini-Circuits POS-1060 VCO module covers 750 to 1060Mhz at a cost
of $15   I've done some experimenting with these VCO's and they are 
truely plug and play, +12dbm output as well.  The problem is that PLL
loop and digital design are areas that I am very weak in.
> 
> Philips has some pretty good low noise bipolars that will work at
> 1296, but you probably want a hot FET if you need < 2dB noise figure.

The the preamp, I'll probably use a MGF1304 or maybe one of the
new NEC devices that I'm experimenting with.
> 
> The only way to make filters in an amateur environment is to print them.
> Stripline is way better than microstrip.  You'll need teflon-glass, not
> FR4/G10 material.  Waveguide would work, but WG is humongous at 1296.
> Maybe somebody makes ceramic filters at 1296, but I think it's unlikely.
> (Unless they're made for an FM ht at that band.  Try Murata and Toyocom.)
> You could conceivably make resonators out of orange-juice cans, but I have
> found that this kind of thing is not too stable, particularly if you want
> to be a rover, with packing and unpacking and temperature variations.  I'm
> thinking of the re-entrant cavity type resonator, with probe or loop
> coupling and some kind of variable capcitance element at the hot end.
> Maybe if you made some out of, say, 2" diameter copper pipe, or maybe
> brass sink-drain pipe, they'd be stable enough, I don't know. You'd
> probably need at least 2 poles.  Put them _after_ the preamp, unless
> you have a really terrible environment. Anything you put before the 
> preamp increases the noise figure by the value of its loss.
>
Right.  On my current designs I use homebrew helical resonators.
They are big, hard to build and work great.  Mechanical stability
as you obsurve is vital.  My resonators are built of silver plated
brass and quite rigid.  Next time I'll use the body of some old
Motorola business band radios resonator as the starting point and
save myself a lot of work.

As for the poles you are right again.  On my 222Mhz transverter, 
two poles were not enough.  Three poles did the right job.  I used
the design charts from the ARRL Handbook to design the resonators
and they were right on.
 
> I'm partial to diode double-balanced mixers, altho a lot of people
> commercially are now using Gilbert-cell active mixers from Philips, 
> National, HP, etc.  These Gilbert-cells usually have NF around 14 dB, 
> so you need a _lot_ of preamp gain.  Also, the output impedance is no-
> where near 50 ohms, so you have to build a tuned matching network.

> That's my 2 cents worth.  Good luck.
> 
> --doug, wa2say 

Thanks Doug, all opinions are welcome!

--73-- David WA0AUQ
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