Plessey PTR 1851J

There's not a lot of info on the 'net about these.

OK so it's a Plessey "Smalltalk" VHF Manportable with 16kbps speech crypto. One would think there would be a processor in there but nope, CMOS only. And not a lot of that, for what it does. Date codes are mostly 1984.

30-76 MHz is 1840 x 25 kHz. So channels 800 to 960 will fall in the 6m Amateur Radio band,

At this stage I know almost nothing about these radios. I don't even know what the IF freqency is. Or how the channels work. I'm guessing as to the functions of the various boards... Reverse Engineering in progress.

Batteries are AG10 / LR1130 A.K.A.

Front view. Note how eager I was to get started with the reverse engineering, the top of the knobs come off exposing the screw to loosen them.

The pipe clamp around the antenna connector is because there's a switch that disables things when the antenna is not screwed in. And the radio didn't come with an antenna -- it came with a pipe clamp.

Board 1: Receiver (?)

419/1/73392 Serial Number 843Z

SO41PFM IF Amplifier with Demodulator
TBA820Audio Amplifier
4051 x28-channel analog multiplexer/demultiplexer
4066 x2Quad analog switch
Cathodeon Crystal Filter Type BP 4643-00

Cathodeon Crystals started off as a division of Pye, and radios like this one (with only one crystal for 1840 channels) helped put them out of business.

419/MB/73393 SH.2 ISS.3

Board 2: VCO and PLL

419/1/72478 Serial Number 0843Z


4008 x34-bit binary full adder
4011Quad 2-input NAND gate
4013Dual D-type flip-flop
404012-stage binary ripple counter
4059Programmable divide-by-N counter
4069Hex inverter
4070Quad 2-input XOR gate
4072Dual 4-input OR gate
4081Quad 2-input AND gate
SP8655A200MHz divide-by-32 prescaler
SL622CAF Amplifier, VOGAD & Sidetone Amplifier

4059 Mode

Board 3: Control

419/MB/70016 SH.1 ISS.2

4001Quad 2-input NOR gate
4011Quad 2-input NAND gate
4017Decade counter with 10 decoded outputs
4027 x2Dual J-K master-slave flip-flop
4029Presettable up/down counter, binary or BCD-decade
4042 x4Quad D-type latch
4049 x2Hex inverter
4069Hex inverter
4073Triple 3-input AND gate
4081Quad 2-input AND gate
4093Quad 2-input NAND gate, schmitt trigger inputs
4175Quad D-type flip-flop
4502Hex inverting buffer (tri-state)
4519Quad 2-input multiplexer
4520Dual 4-bit binary up counter
4555Dual 1-of-4 decoder/demultiplexer
45854-bit digital comparator
74C89 x264-bit (16 x 4) RAM

OK, so this board has 16 bytes of CMOS RAM.

419/1/70013 (?) Serial Number 0843Z 419/MB/70016 SH.2 ISS.3

Board 4: Power Stage, Rx/Tx Switching

419/1/70007 Serial Number 0842Z

DV1210S, 10W N-Channel 175MHz FET


Front Panel / Control Board

The break in the trace looks like the PCB was manufactured like that?

The front panel PCB has

4511BCD to 7-segment latch/decoder/driver
4529Dual 4-channel analog data selector/multiplexer

Flex PCB

I numbered the flex PCB traces from the top, 1-25, as a handle for reverse engineering the schematic.


The backplane is 4 x DIN41612 AB (Type B)

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