[Premium-Rx] Looking for Rare Part for Rare Receiver

[John Miles]

>
> I have acquired a PR-700A spook radio (for surveillance and
> monitoring) made by Micro-Tel Corporation in Baltimore.  It is
> very interesting radio and is operational on the bands up to 30 MHz.
> It has a defective wide-band amplifier module which is used on
> all ranges above 30 MHz (it goes up to 2 GHz).
>
> This module is a small cube of aluminum about 1 " on a side with
> mini coax in and out. plus a power terminal for 15 VDC.  The
> amplifier inside is an AVANTEK UTO-2021 thin-film circuit.
> I have found a supplier or twp for a new UTO-2021 circuit but
> they want over $200 for it.  Does anyone out there have something
> similar that might work?  I know it is along shot, but I needed
> to inquire. This is a wide-band amplifier that the antenna signal
> passes through and would need to be usable over the 30 to 2000 MHz range.
>
> If anyone has something that might work or has any advice for me
> (other than "buy the $200 unit") I would be interested.

There is nothing special about the UTO-2021 -- in fact it's a
low-performance part by the standards of today's MMICs.  You could replace
it with one of these ( http://www.minicircuits.com/pdfs/VAM-6+.pdf )
dead-bug mounted on a piece of copper-clad board.  IP3 and gain should be
similar, and the NF will be improved.  Cost: $1.40, plus a dropping resistor
and pair of coupling capacitors.  I wouldn't bother with a choke since the
resistor will be 680 ohms for Vcc=+15V.

Or you could splurge and get a preassembled test board for the VAM-6+ for
$59.95.

If this thing is actually connected to an antenna, I'd take the opportunity
to upgrade to something with a better IP3.  The GALI-51F raises the ante to
$2.60 and the IP3 to +32 dBm.

Caveats: 1) Supply current will be a bit higher if you use the GALI-51F, but
probably not by enough to hurt anything.  2) The first few times you
dead-bug a MMIC you should borrow a spectrum analyzer, if you don't already
have one, to check for parasitics.  A copper-foil shield around either the
input or output components will typically get rid of the most common ones,
which show up when the lid goes on the box and turns it into a closed
cavity.  Not a huge inconvenience, considering the bang:buck ratio.

-- john, KE5FX