MM4001KB RTTY

"It came without any instructions..."

MM made a range of RTTY decoders and transceivers but the only information I have are data sheets from their catalogue and a review in May 1983 Ham Radio Today (thanks G4KFK!). I've seen a lot of requests for instructions and manuals for these devices posted in the various amateur radio forums (mysef included!) without success so it looks like it will be a voyage of discovery to tinker and document the one I've acquired.  

All were based on a Motorola MC6802 and MC6821 PIA. The 6802 is a development of the original Motorola 6800 and uses the same instruction set. There appears to be 1k of static RAM dedicated to the CPU and the firmware resides in a 4k 2732  EPROM.  A Thomson EF9364 is used as the CRT controller with another 1k of static RAM.

I have dumped the 2732 EPROM and run it through a disassembler. It's located at F000h - FFFFh in memory as the M6800 reset vector is FFFEh. Here's the disassembled code.

The transceivers (4000, 4001KB) were supplied with a RCA VP601 keyboard. which is based around a membrane keypad, a CDP1832 as a lookup table and a selection of CD4000 CMOS logic. MM applied their own branding sticker to the keyboard and a cable terminated with a 25-way D type.

Operating appears to be fairly straightforward, assuming you are familiar with RTTY baud rates and shifts in use for Amateur Radio and Commercial signals. Long gone are the days when there were numerous press stations on shortwave to decode and enjoy, but there is still the German Meteo station which broadcasts with 50 baud 425Hz shift on 4583 kHz, 7646 kHz, 10100.8 kHz. When not transmitting bulletins, it continually transmits it's ID and RYRYRY tuning signal. 

Operation and keyboard interaction that I've figured out so far... Read the description on the data sheets for more clues.

• The device will be in receive mode when powered up. Set switches for centre frequency and baud rate.

• Touching any key on the keyboard will put the device into PRIME mode. Enter your callsign, press the ESC key. Enter your QTH, press the ESC key again and you will be in the menu. Here you can load the memories and do other TX things or just return to receive mode. 

• CTRL-R will change immediately to receive mode.

• CTRL-K will change immediately to transmit (keyboard) mode.

5-pin locking DIN connector (240°)

1.  not connected?

2. TX audio output 100mV pk-pk square wave

3. power 0 volts

4. Audio input - in parallel with AUDIO IN phono socket

5. +12V power in

8-pin locking DIN connector

1.  loopback plug connected to 6

2. loopback plug connected to 4. Demodulator out/TTL in 5v

3.  loopback plug connected to 5

4.  loopback plug connected to 2

5. loopback plug connected to 3

6. loopback plug connected to 1

7.  +12v from pin 5 on the 5-pin.

8.  0 volts

I've scanned the relevant pages from my Microwave Modules catalogue - unfortunately they didn't include a publication date. The test sticker underneath my unit is dated 1984.