|DEDICATED TO THE MEMORY OF ANTHONY (ANT) MARTIN M1FDE 5th January 1967-20th September 2008|
This is a page about the RC690 transceiver.
The RC690 "Repeater Mobile" is a boot-mount transceiver with a separate control head unit. It was made in the 1980's by Marconi, Chelmsford and sold to many police forces & ambulance fleets. "Repeater Mobile" comes from its ability to act as a repeater for the Police handhelds when the officers leave the vehicle. It is also classed a "Wideband" mobile due to the wide tuning band without factory realignment. RC690 is capable of full-duplex operation with two antennas but may also be fitted simplex with one.
I'm told about 3000 were were made.
There exists several variants:
As I don't have the 70MHz unit all the following applies to the 144MHz radio.
My RC690s were purhased for small change at the Stevenage amateur radio show. I have 3 sets complete with handsets and control units. Some had facilities bypass plugs and one had a short power lead with inline fuse. The radio units were all fairly dirty, but the control units were clean.
I have made my own interconnect cables.
RC690 is a duplex radio; it has separate Tx and Rx synthesisers and antenna connectors.
RC690 can also work in simplex mode; it simply mutes Rx audio in Tx! There is an antenna switch relay provided for simplex single-antenna use.
RC690 can also operate as a repeater, using EEA selcall tone access. NB: no CTCSS. In this mode of operation it scans two channels for activity and will activate repeater operation in the appropriate direction.
The RC690 also has a PA (public address) mode which delivers substantial audio power to a speaker on top of the police car or perhaps behind the radiator grille. The "PA" button and and PA volume knob on the control unit control this function.
The radio supports detection and generation of 5-tone EEA-standard selcall tones. In fact the head-unit's tone generator can send almost any in-band tone (eg. 1750 Hz). Firmware only uses selcall for validating access to the repeater function.
The radio has a time-out timer which bleeps you shortly before expiry and then cuts off the Tx.
The radio is linked to the control head via a 15-way female-female D-type cable with all pins wired one-to-one.
The 15-way male "facilities" connectors on both the radio and control head must be fitted with link plugs to bridge the audio and PTT through.
A handset connects to the head unit with a 5-pin DIN plug; it is a black telephone-type with a pressel suitable for duplex working.
Varicap voltage tuning is used in the Tx & Rx synth LO filters and Rx front end RF filters. No re-adjustment is needed for 2m band - unless you messed with them! It is designed like this to support a wide Tx/Rx split for duplex/repeater working and to work with Tx & Rx either way round. If you tweak, be aware the filter centre-frequency will shift with radio tune frequency; ie. set radio for 145MHz and set filters on 145MHz. Don't even look at them if the synths are off-frequency. Varicap tuning voltages are derived from the synth loops.
Receiver RV1 - Audio out to head unit level
Mod-Reg RV1 - +9V supply current limit
At present I can't say how the PSU should be set up, don't fiddle. When I say "current limit", it's a protection of the LDO regulators that acts to prevent overdriving the pass transistors if the supply is overloaded or the input voltage is too low.
The channels are stored in the radio in battery-backed RAM.
Each channel can specify Tx & Rx synth setup, time out timer, CTCSS modes, and duplex mode. There is also some non-channel data including selcall identity and scanning dwell times.
The RC690 is intended to be loaded from a fill-gun unit connected in place of the control head. At the moment I have no idea what the gun looks like, although it appears to be the same gun as used with RC640. Although the channel data is different, it doesn't matter to the gun as it simply transfers a RAM-image. The gun, in turn, received its fill from another device. In later days PC-based software was produced to generate radio configuration files and transfer them to the fill gun.
The gun essentially transfers records of intelhex using a serial handshaking protocol. Fills have versions and editions and radio types, and so the appropriate fill selection becomes automatic when simply updating a radio. Fills also have a "status block" which contains a checksum and version info; checksum is only ever checked after filling and never at powerup.
The serial interface between the radio and control head is RS422; 2400 baud, 1 start, 7 data, odd parity, 1 stop. At powerup, the radio sends the letter "C" at intervals and awaits an "H" reply from a control head or a "G" from a fill gun.
Big knob - push/pull the knob in to switch off/on. Turn to set volume. If it won't click when you push/pull then tighten the allen grubscrew!
The decimal point in the display shows it's on. If it's dim that's normal; if it comes on bright it's an indication the CPU is not running and is not scanning the display & polling the keypad.
Channels are entered by pressing "*" followed by two digits and another "*". "00" is illegal.
# key (cancel) - cancels an unfinished entry or cancels repeater mode.
HP key - (REPh) - repeater mode
R key - (REPnn) - repeater mode. Follow by 2 digit channel and "*".
The difference in REP and REPh is the channels used. My theory is that one offers a local repeat between handhelds and the other between handhelds and HQ.
T/T key - function is unknown. The key is blank on some units. A selftest key?
S key - shows the 5-digit selcall number. At one time it was also possible to edit the selcall.
PA (public address) key - enables Public Address mode, indicated by green LED. Mic no longer activates transmitter but audio goes to speaker output on radio unit. This feature is almost a by-product from the audio amplifier used for high-level AM modulation of the RF PA.
Between PA key and LP key is a small knob which adjusts the PA volume.
LP (lamps) key - turns off/on the keypad illumination (on by default).
Between LP and SQ is a small knob that dims the display and illumination.
SQ (squelch) - pressing this toggles squelch-mute. Squelch is on by default.
LS (loudspeaker) button - enables the loudspeaker, indicated by the amber LED. Speaker is always muted when keyed in Tx Duplex to prevent feedback.
The radio chassis is DC isolated from supply 0V although chassis is RF ground.
The magnetic mic is connected between 1 (yellow) & 2 (green).
The earpiece is connected between 2 (blue) & 4 (grey).
The PTT switch is connected between 3 (pink) & 5 (white).
For duplex, some kind of handset or headset is required. I recommend separate ground wires for mic and ear back to the connector to avoid crosstalk. Fist speaker-microphones could be used for simplex if they have separate mic and speaker or if the PTT switch will swop the connections. Note that fist mics usually have PTT-to-ground; to rewire it you need at least 5 wires in the cable.
One warning: Don't short the PTT to +12V as it connects directly to the processor, which will probably die instantly. In fact ESD protection is lacking on many signals. The PTT pin is next to the +12V pin on the facilities connector.
For normal operation, a facilities bypass plug must be fitted at both radio and control head with the following pins linked: