Modifying the UHF M212 Pye Olympic for Packet Radio - Part 1 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The Pye Olympic is a relatively modern PMR radio which has some rather nice features. The diecast alloy chassis houses plug-in modules which can be easily removed for maintenance. The receiver is dual-conversion with a 21.4 MHz 1st I.F. and a 225 kHz 2nd I.F. The M212 is the UHF version which originally operated in either of two sub-bands: T1 405-440 MHz and U0 440-470 MHz. All UHF Olympics are either 20 kHz (Suffix R) or 25 kHz (Suffix V) channel spacing. The T1 Band Olympics are ideal for use on the 70cms band and will give more than 10W output on TX and produce 12dB SINAD for around 0.5 microvolts p.d. RX signal. The U0 Band Olympics will also tune 70cms, but with slightly lower RX sensitivity. M212 Crystal Details: ~~~~~~~~~~~~~~~~~~~~~ The crystals required for 432.675MHz are: TX = 16.0250MHz RX = 16.8176MHz Realignment: ~~~~~~~~~~~~ 1) Remove the plastic front panel by locating the pin on its right-hand side. With a small screwdriver, push the pin in, whilst gently easing the panel off from the right. Do this carefully! 2) Remove the two screws at the front top and bottom, which are now exposed and then remove the covers. 3) Remove the push-on metal covers to access the various boards which need realigning. Rx Alignment: ~~~~~~~~~~~~~ RX Oscillator Multiplier Board: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Locate the RX oscillator multiplier board (4) and with a suitable test meter (+ve meter lead to +ve supply and negative lead to the various test points on the multiplier board ) run through the following sequence: n.b. all the following voltages were measured with a Fluke 77 digital multimeter. a) TP1 - tune C3 for a maximum reading (1.5v) b) TP2 - tune L2 & L3 for a maximum reading (2.5v) c) TP3 - tune L4 & L5 for a maximum reading (1.65v) d) TP3 - tune L6 for a minimum Transfer the test meter +ve lead to chassis and the negative lead to TP1 on the RF amp/mixer board (1) a) TP1 - tune C22 on the oscillator multiplier board for a maximum (0.2V) b) TP1 - tune L9 & L10 on the RF amp/mixer board (1) for maximum c) TP1 - tune C3,L2,L3,L4,L5,L6,C22,L9,L10 for absolute maximum (0.2v) RF Amplifier/Mixer Board: ~~~~~~~~~~~~~~~~~~~~~~~~~ Switch on a signal generator, tune to the selected carrier frequency and set the output level to 10 mV CW. Using a 21.4MHz marker oscillator near to the receiver I.F. amplifier/squelch board (2), tune the appropriate crystal trimmer for zero beat. a) L2, L3 - tune for the best receiver quieting, reducing signal generator output as necessary b) L4, L5 - tune in sequence for the best quieting, reducing L6, L7 signal generator output as necessary L8 c) L9, L10 - tune in sequence for best quieting, reducing signal generator output as necessary On the I.F. amplifier/squelch board (2), locate TP1 and with the digital voltmeter (-ve lead to chassis) connect the +ve to TP1. Increase the signal generator output to about 100 microvolts, then tune T1 and L1 on the IF amplifier/squelch board for a maximum. Modulate the signal generator with a 1 kHz tone at 2.5 kHz peak deviation (for 25 kHz bandwidth: 2kHz peak for 20 kHz bandwidth) and then tune L3 on the IF amplifier/squelch board for maximum audio output. This completes the receiver alignment. The Olympic isn't the most sensitive receiver in the world, but is entirely adequate for packet radio use where signals should be pretty good anyway! Part 2 deals with the TX alignment and TNC interfacing Modifying the UHF M212 Pye Olympic for Packet Radio - Part 2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ TX Alignment: ~~~~~~~~~~~~~ TX Exciter: ~~~~~~~~~~~ Locate Module 8, TX Multiplier/Exciter, next to the Facilities Socket. Connect a power meter/50 ohm load on the antenna socket and the digital multimeter negative leg to to chassis. a) TP1 - Tune L1 and L2 for a maximum (3.1v) b) TP2 - Tune L4 (underside) for minimum (1.8v) c) TP3 - Tune L6, L7 (underside), and L8 for a maximum (3.8v) Repeat steps a, b, and c, for an absolute maximum on TP3. d) TP4 - Tune L8, L9 for a maximum e) TP4 - Tune L1 to L8 for an absolute peak (1.1v) If tuning a U0 band set, locate L17 and L18 and place the cores at the bottom of their travel. With a T1 band set, leave the cores of L17 and L18 where they are. With a diode probe on C36 (collector side) i.e. the metal adjustment screw, tune C31 (underside) for a maximum. Transfer the diode probe to C42 (positive) i.e. the metal adjustment screw, and tune C36, L17 and L18 for a maximum. When correctly aligned, L17 and L18 (band pass filter) should be at the same position in their formers. Transfer the diode probe to C44 (collector side) i.e. metal adjustment screw, and tune C42 for a maximum. Tune C31, C36, L17, C44, L18, C42, in that sequence for a maximum. P.A. Module: ~~~~~~~~~~~~ Now, watching the RF output meter, tune L1 and L2 on the rear, panel mounted P.A. Module (9). Tune them for maximum RF power output, then retune C44 for an absolute maximum. There should be approximately 10W RF output from the M212, however, most have a power adjustment control: RV1 on the PA Board. Maximum power corresponds to RV1 being fully counter-clockwise. Set RV1 for 10W RF output. The TX peak deviation is adjusted by RV1 on the Transceiver Audio Board (7) and should be set for +/- 3.25kHz peak with the highest audio tone from the TNC (using the CAL routine) for use on Packet Radio. This concludes the TX alignment. Facilities Socket: ~~~~~~~~~~~~~~~~~~ On the left-hand side of the Olympic, a slide-in facilities PCB holds a SELCALL board; a squelch busy lamp, and push switch. The facilities PCB fitted in my Olympic also had a small 12V reed relay with c/o contacts which was utilised as part of the modification detailed later on. The facilities PCB plugs into socket SKB, which also carries most of the connection paths needed for the TNC, although the microphone socket SKA (a 270 degree locking DIN type), linked to SKB, is used as the TNC interface. Socket SKA/SKB Details: ~~~~~~~~~~~~~~~~~~~~~~~ SKA Microphone Socket Pin 1 Microphone input Pin 2 Microphone screen (-ve) Pin 3 TX oscillator 10v switched input (PTT) Pin 4 Earpiece audio Pin 5 +10V regulated SKB Facilities Pin 1 -ve line Pin 2 Non de-emphasised RX audio Pin 3 Microphone Input (Pin 1 SKA) Pin 4 Pin 3 SKA Pin 5 Pin 5 SKA Pin 6 TX audio output Pin 7 TX oscillator +10v switched (Pin 3 SKA) Pin 8 RX audio output (from top of volume control) Pin 9 +13.5v Pin 10 Busy lamp (0V with squelch open, +13.5v squelch closed) Pin 11 +10v regulated Pin 12 RX audio input Pin 13 Pin 14 -ve line Part 3 details the modifications for Packet Radio use. Modifying the UHF M212 Pye Olympic for Packet Radio - Part 3 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Packet Modification: ~~~~~~~~~~~~~~~~~~~~ Remove the facilities card (CT35013 - module assembly) and strip off all the components. The one in the Olympic I have here had a bare motherboard with smaller CTCSS cards bolted to it. The extra switching stages necessary for packet work were all built on a small piece of Veroboard measuring 74mmx58mm. The modification provides: 1) a PTT line compatible with most TNCs 2) a squelch "busy" lamp 3) a TX key for test purposes The busy lamp and TX push button were already mounted on the module assembly. Link Pins 8 and 12 on the module assembly to provide RX audio in the speaker (if required) Pin 1 is at the left, looking at the top of the board. PTT Modification: ~~~~~~~~~~~~~~~~~ The PTT on the Olympic is a switched +10V line to the TX oscillator, this is incompatible with most TNCs, and the reed relay, from the facilities board, is used to switch the oscillator positive voltage rail. It is necessary to make the TX PTT compatible with the TNC. Most TNCs earth the TX PTT line via a switching transistor. To achieve this on the Pye Olympic, a small reed relay is used to key the +10v TX oscillator line, the reed relay itself being switched by a BC477 PNP transistor. ............................... To Pin 9 : : RLA make contacts to Pin 7 of SKB (+13.5v) : --- and Pin 11 SKB RLA / \ D1 : ~:~ 1N4001 :......: : / To Pin 5 -----: 4.7K :--: BC477 of SKB (PTT) : \ : collector : To Pin 1 of SKB :......................... -ve line RLA, a 12v reed relay, was already available on the plug-in facilities card and was re-used. The diode D1 protects the BC477 from damage by back EMF from the coil of RLA during switching transients. The BC477 emitter is connected to the relay and its collector to -ve (ground) The two make contacts of RLA are used to switch the 10v regulated line to the TX oscillator. TX keying is now achieved by earthing the base of the BC477 via a 4.7K resistor. A small locking push-switch was available on the module assembly I had and this was used to provide a TX key for test purposes. Busy Lamp Modification: ~~~~~~~~~~~~~~~~~~~~~~~ A busy lamp indication of squelch operation is relatively simple to achieve, and is similar to the PTT modification detailed above. A BD238 PNP plastic power transistor is used to switch the busy lamp indicator bulb which is already mounted on the module assembly. ........................ To Pin 9 : of SKB (+13.5v) : LP1 (Busy Lamp) : : : / To Pin 10 -----: 10K :--: BD238 of SKB (RX Busy) : \ : collector : To Pin 1 of SKB :......................... -ve line The interface to the TNC is now via SKA, the microphone socket. Very conveniently, the pin-out connections are identical to those on the Pye Westminster (which I use on 4m), making testing and setting up simple. SKA Pin Out (after modification): ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Pin 1 Microphone input Pin 2 Microphone screen (-ve) Pin 3 Common (-ve) Pin 4 RX audio (earpiece) Pin 5 PTT The modification detailed above works very well here at G3VMW, however, I would be the first to accept that there may be better ways of achieving the same result. I am now working on removing the pre-emphasis on TX and de-emphasis on RX. Pin 2 of SKB has RX de-emphasised audio already available and it may be possible to utilise this. If I've re-invented the wheel, I apologise! This information is sent out to try and encourage people to have a go at modifying ex-PMR radio gear which is usually the cheapest way of getting on Packet Radio. Modifying the UHF M212 Pye Olympic for Packet Radio - Part 4 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Addendum: ~~~~~~~~~ Part 3 of this series dealt with modifying the M212 UHF Olympic for packet radio. The original radio which I modified did not have a 15 Way D-Type, External Facilities Socket on the rear panel. I have subsequently modified another two Olympics which did have the D-Type socket, and there are some slight differences in wiring configuration, particularly around the microphone Socket SKA, which is used as a TNC interface. The wiring MUST be altered as follows or the modification will not work correctly on this type of M212. On Olympics WITHOUT the D-Type socket, wiring is as follows: SKA Pin 5 (Yellow) to SKB Pin 5 (+10v regulated) SKA Pin 3 (Green) to SKB Pin 4 (TX oscillator 10v switched input) SKB is the horizontally mounted edge-connector socket, on the left-hand rear of the M212, when viwed from the front. SKB mates with the slide-in Facilities Card which come in various configurations. On Olympics WITH the D-Type socket, wiring is as follows: SKA Pin 5 (Yellow) to Motherboard Pin 33 (+10v regulated) SKA Pin 3 (Green) to Motherboard Pin 32 (TX oscillator switched input) SKB Pin 5 (Green) to (15 Way D-Type) SKD Pin 12 SKB Pin 4 (Yellow) to (15 Way D-Type) SKD Pin 4 Pin 33 on the Motherboard is a solid connection to the +10v line from the 12.5V Restrictor & Regulator Card (6) To enable the modification I detailed in Part 3 to be compatible with this alternative Olympic configuration, the following modification is necessary: a) Pull off the two connections to the Motherboard, Pins 32 & 33 (adjacent to SKA) which go to Pins 3 and 5 of SKA. b) Unsolder the yellow wire from SKD on Pin 4 and the green wire on Pin 12. c) Connect the yellow wire which is connected to SKB Pin 4 to the green wire from Pin 3 of SKA, enclosing the joint with a rubber sleeve. d) Connect the green wire which is connected to SKB Pin 5 to the yellow wire from Pin 5 of SKA, enclosing the joint with a rubber sleeve. It helps to remove the screw holing the supply line filter to the rear panel, and moving the filter slightly to gain access to these connections. The object of the excercise is to ensure that Pins 3 & 5 of SKA connect directly to Pins 4 & 5 of SKB respectively, so that the reed relay can switch the +10v line to the TX oscillator. Modifying the Pye UHF M212 Olympic for Packet Radio - Part 5 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Full Duplex Operation: ~~~~~~~~~~~~~~~~~~~~~~ Parts 1-4 of this series dealt with modifications to the M212 Olympic for use on 70cms Packet Radio. This latest modification has a number of uses, including Packet Radio. The UHF Olympic can be converted quite easily for simultaneous TX and RX operation, i.e. Full Duplex, which allows it to be used for various other purposes: a) Full Duplex "local" links b) Portable, easily set-up repeater for RAYNET use Thanks to Ian Pomfret, G6MHO for implementing a series of technical suggestions I made, and proving that the theory really does work in practice! Ian now has an M212 Olympic running full-duplex on 434.625 RX and 439.225 TX. He contributed significantly to the following information. Introduction: ~~~~~~~~~~~~~ Close examination of the M212 reveals the following features: a) Completely independent TX & RX modules b) Excellent interstage screening c) Spare position for an additional BNC socket on the rear apron It is possible that a full-duplex version of the Olympic was marketed in view of the last feature. Technical Details: ~~~~~~~~~~~~~~~~~~ On TX, the Olympic switches the +12.5 line to the RX Oscillator via RLB on the Antenna Filter and c/o Relay Board (10) Pin 6. To work in full-duplex mode, the +12.5 line must be taken permanently to Pin 13 of the RX oscillator so that it can run all the time. A +10v muting line is applied via a 3.3K resistor (R1) to Pin 11 of the Transceiver Audio Board (7) which is located immediately to the right of the TX Driver Board (4). This +10v line shuts off the Squelch 'B' I.C. TF2 FU00533 and kills the audio output. If you unplug Board 7, on the motherboard, you will see the 3.3K resistor (R1). On the underside of the motherboard there are two back-to-back diodes (D2 & D3) which connect to the 3.3K resistor. That junction is the point where the +10v muting voltage is applied via the PTT line. Under normal circumstances, the +10v mute line is switched by the PTT switch in the hand microphone, but with the packet radio modification, the reed relay does the switching. Full Duplex Modification: ~~~~~~~~~~~~~~~~~~~~~~~~~ a) Disconnect the the coaxial cable from the RX RF Front End Board (1) SKF which connects to the Antenna Filter & c/o Relay Board (10) Board 10 is immediately in front of the PA Module (9) and unplugs quite easily. b) Fit another 50 ohm chassis-mounting socket on the rear apron of the M212 chassis. There is just space to mount two BNC sockets, one above the other on the plate which carries the original antenna socket. c) Make up a slightly longer lead using miniature 50 ohm coaxial cable (preferably high quality as per original) from SKF to the RX antenna BNC. Carefully dress the new coaxial to prevent desensing problems later on. Some trial and error might be required here. The original antenna socket is now used for the TX antenna. The RX front end doesn't have the benefit of the TX low pass filter in circuit now, but this has not proved to be a problem in practice. d) Remove the wire link between Pins 13 and 15 in the Crystal Oscillator compartment (on the motherboard). Connect an insulated wire between Pin 13 and a suitable 12.5v permanent supply point on the motherboard. e) Remove the Transceiver Audio Board (7) and in this compartment locate R1 3.3K on the motherboard. On the underside of the motherboard, remove the two back-to-back diodes D2 & D3 (D2 anode connects to R1 and the TX +10v switched line) This completes the modification for full duplex working. Obviously, separate TX and RX frequencies must be used. Preferably with as much frequency difference as possible, to avoid any RX desensing. Ian G6MHO @ GB7CRG has offered to answer any further queries and I will also assist if required. Steve G3VMW @ GB7LDS PORTED AND REALIGNED FROM PC TO AMIGA FORMAT BY BOB G0LBQ - N6XDI.