[Premium-Rx] IF conversion unit - help requested

[Michael O'Beirne]

Good afternoon members from a very cold and snow-laden England.  FYI London
has virtually come to a halt with no buses, no Underground and very few
trains.  I'm stuck at home - hence this.

I am looking for information on a unit that looks as if it was made for the
Royal Navy, described on the lid as "100 - 455 kHz.   UP CONVERTER     51 -
2648"

Externally it is a very solid diecast box (4mm thick) with a sealing gasket
in the lid.  The external dimensions are 4.9 in across (12.5cm), 3.1 in
(8cm) wide and the depth is 2.2 in (5.7cm).  I have found near identical
ones in an old 1990 RS catalogue.

The colour is light battleship grey.  There are two dark grey slim labels
screwed to the side marked:-
a. with the NSN : 5865-99-547-3164; and below it
b. "84 RAZ 101".

There is also the usual black MOD Record label with no strike offs.

This is typical RN equipment livery.

There are two silver-plated BNC square flanged connectors, one on the long
face marked "INPUT" and one on the short face marked "OUTPUT, and a standard
9 pin male D socket on the other short face.

Inside is a HC-6U crystal on 3550 kHz, a ferrite potted inductor resembling
a mini "Vinkor", a MCL SRA-3H quad mixer package, quite a few BC107
transistors (difficult to read).  Two of the transistors are enclosed in a
small heatsink made up of a solid lump of metal and a third has the usual
wriggly circular slip-over heatsink.   I guess these are for LO injection.
There are also the following chips

SN 54132J
SN 54175J
5474J (Texas Instruments).

According to my old Mini-Circuits catalogue the SRA-3 requires a +7dBm LO
injection and covers the range 25 kHz to 200 MHz.  The LO to IF and LO to RF
isolation is about 60dB.

Clearly the 3550 kHz output from the crystal oscillator is divided by 10 to
give 355 kHz. The tunable "Vinkor" inductor is near the crystal and
presumably is tuned to 355 kHz to clean up the output of the decade divider,
and the output is amplified and applied to the DB mixer to mix with the
100kHz IF input giving 455 kHz out.

The 9 pin D connector supplies power:  there are three leads - black to
chassis, green and yellow, and there is some filtering.

It's beautifully made.  The holes for the BNCs for example are all metric
tapped rather than using nuts on the bolts.  The PCB seems very elaborate
for a simple converter.  The resistors and capacitors look high grade items.

I'd love to have more info on this unit, particularly the circuit and power
supply requirements.  I imagine it was used with the 100 kHz output of a
receiver, but I cannot recollect any fairly recent one used by the Royal
Navy that has an IF output on 100kHz.  The last I think was the ancient
Outfit CJK (RA117E plus adaptors).  Nor can I imagine what the Navy wanted
at 455 kHz except perhaps to feed into a unit incorporating 455 kHz filters.

Thanks guys
Michael O'Beirne
G8MOB