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Simple Conversion

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By Jan Buiting, PE1CSI, Philips Mobile Radio Collection, Sibbe, The Netherlands. Email info@pmpc.myweb.nl

Article originally published in Radio Today September 2000, updates included in this web version.

Warning: the Simple Conversion described here has been tested on the following radios: FM1100 RA911, FM1200 STM22, FM1200 STM23, FM1100 SU0, all with the numeric keypad head.

Warning: The Simple Conversion is not suitable for FM1200 radios with a Type-1 control board. This includes the ex Electricity Systems VHF FM1200 SB014 which is around in vast quantities in the UK. This radio can only be converted by means of the Extensive Conversion.


Provided you can get hold of the right versions, the Philips FM1100, FM1200 and FM1300 PMRs (Personal Mobile Radios) are probably the easiest converted ex-PMRs for amateur use. 
In the FM1100 no conversion is required except changing two EPROMs and one EEPROM, while in the FM1200 and FM1300 the extra work consists of relocating 1 (yes, one) small PCB track. What's more, these brilliantly designed radios require no alignment whatsoever. Thanks to their compact and robust construction, LCD readout and lush transmit power levels of up to 25 watts (6 watts UHF in Germany), the 1100, 1200 and 1300 are highly suitable for mobile use.

About the FM1200 UHF

In all likelihood, any Philips PMR Type FM1200 STM22 found on rallies, car boot sales etc. was at some time part of a large trunking radio network operating in the UHF band. The FM1200 was originally designed around 1990. This once very advanced, very expensive microprocessor controlled FFSK transceiver consists in essence of three modules:

  1. Control Board, holding two microcontrollers (type 80C31) with RAM, EPROM, etc. plus an amount of digital electronics. The lot is in charge of nearly all control systems in the radio. The trunking section on this board has no value for radio amateurs. The control board may be found under the smaller cover.
  2. Analogue Board, containing all analogue electronics, the PLL, VCO, RF, IF and audio amplifiers, etc. For convenience's sake, we also count the transmitter PA in this section. Remarkably, the entire transmitter and receiver are completely adjustment-free between the specified band limits of 400 and 440 MHz (TM band). So, readjustment is never necessary after any frequency change between these band limits, as the receiver and transmitter are automatically kept tuned to maximum sensitivity and output power respectively. This system is called Auto RF Tracking and is implemented by two dozen varicaps tuned by D-A converters, all under control of the 80C31. The analogue board greets you if you open the larger cover and remove the internal screening plate.
  3. Console, this is the user control part with the LCD. The console contains its own microcontroller system, again built around an 80C31. So far I came across 3 different types of console: 'standard', 'basic' and 'keypad'. For this conversion it is assumed that a radio with a keypad head is available.

The three modules that make up the radio communicate via an internal bus en simple pinheaders and sockets. The original EPROMs contain about 32 or 64 Kbytes of machine code for the 80C31s. Years ago, at the Simoco headquarters in Cambridge, the FM1200 was jokingly called ‘a computer acting as a radio’. The FM1200 version STM22 supplies 25 watts of RF power, is suitable for the 12.5 kHz raster, and covers 400-440MHz. In other words, it should be ideal for radio amateur use.

The radios in the FM1000 series are easily assembled for local control (i.e., with the console mounted on to the radio) or for remote control (console mounted on the dashboard and radio somewhere else in the car).

The conversion described here was first tried out by Gerrit Speelman PA1MT. Since then it has been carried out more times than I care to remember, with a good success rate. The conversion typically takes less than 15 minutes to complete.

All the designing, debugging and head scratching has been done for  you and comes in the form of this web document and three ICs: two EPROMs and one EEPROM. As far as transmit power levels are concerned, the FM1200 STM22 puts competing UHF radios like the SE Condor 46 and some other ex-carphones to shame. In practice, 25 watts of RF is a comfortable level to have available on 70cms, providing much more ‘push’ than a 6 or 10 watts rig, especially when going mobile.

The conversion consists of three steps, or, if your like, 'phases'. To begin with, new software is fitted in the console (EPROM). Next up is the only bit of solder work you'll have to do: relocating a single PCB track. This effectively puts the internal trunking processor to sleep, enabling the FFSSK FM1200 to behave like a regular NBFM transceiver. Next, we fit a new ‘firmware’ EPROM in the radio itself. Finally, a suitably reprogrammed EEPROM is fitted. This is an 8-pin IC containing about 1,000 user settings.

FM1200 conversion, step-by-step

General tips

Tidy up your workspace. This reduces the risk of losing vital screws and other parts.
If you remove an EPROM or an EEPROM IC, make a note of how it was mounted on the board.
New EPROMs often have their pins too wide apart to allow immediate insertion in a socket. Align pins as required. This is easiest done by holding the device so that one row of pins is flat on the work surface, and then pulling the IC gently towards you while keeping the pins firmly pressed against the table top.
Do not switch the radio on before it has been completely converted. When the FM1200 is switched off, user data is written into the EEPROM, overwriting previous settings.
Follow this conversion description in a step-by-step manner, do not skip anything unless explicitly stated.
Never leave the power supply switched on while working on the radio.
Although the transmitter PA stage is ‘fool-proof’ by almost any standard, always connect a dummy load or a suitable antenna.
If you suspect your antenna matching is less than optimum, use Low Power (6 watts) and keep TX time to a minimum. A 2m band antenna does not radiate at 70 cms.

Converting the console

a) Use the microphone to tilt the radio front side up.
b) Release and remove the two Pozidrive screws at the sides of the radio.
c) Detach the console from the radio by gently pulling it towards you.
d) At the rear side of the console, you will see 4 rather deep screw holes. The outer two contain Pozidrive screws that have to be released. With the screws removed, put the plastic piece carefully in front of the radio, with the front side flat on the working surface, so that no strain is exerted on the 'flex strip' now in view.
e) Release the 8-way cable by carefully prising it away from and out of the white pinheader, using the tip of a small screwdriver. Be careful with the gold-coloured flex cable near the microphone connector. Leave the flex cable in place!
f) Remove the volume control knob by pulling it off the spindle.
g) Release and remove the four screws in the holes at the rear of the console, then pull the plastic section slowly and gently away from the metal chassis. Keep the console as close as possible to the table top, with the on/off knob down, then look and listen carefully what happens. Why? Well, a minor catastrophe that can happen at this point is that the on/off switch comes apart, literally. Don't panic! If you can recover all the parts it is possible to reassemble the switch, although that requires precision and good eyesight.
h) Release and remove the two screws on the LCD board. One is found near the volume control, the other, in between the keys of the numerical keypad. These screws may require more than usual force to release!
i) Prise the tip of a sharp screwdriver between the PCB and the metal chassis, roughly between the two sets of 8 solder pads near the top edge of the board. Prise carefully and remove the LCD board.
j) Remove the PROM type AT27C512 (it usually has a sticker on it). Throw it away, the device is almost impossible to erase and re-use.
k) Fit the new EPROM type 27C512 programmed with the new display software from the File Downloads page. The notch in the EPROM should be at the side of the 7805 voltage regulator.
l) Check if the little PCB track ‘LK4’ (left, below the EPROM) is fitted to the right-hand side position. If not (rare), then cut the track and connect the centre pad with the right-hand pad.
m) Remove the acrylic film from the LCD frame by pulling it out from the right-hand side. Details on how to make or obtain a new film are given a bit further on.
n) Re-assemble the console using the reverse order. Be sure to fit the LCD board properly to the basic part. For aligning the two, use the screw holes as guides.

Converting the radio proper

a) Turn the radio with its front towards you, and the small cover up.
b) Remove the small cover (1 large screw).
c) Some radios contain a plug-on daughterboard in the top right-hand corner of the control board now in view. Remove the daughterboard, it serves no purpose in the converted radio.
d) In some older radios, trunking EPROM IC549 is fitted in a socket. You are in luck. Remove the EPROM from the socket and continue with step n).
e) Remove all screws that secure the Control PCB (and the 7805) to the case.
f) Lift the PCB at the front edge, where it has two pinheaders at the solder side. This best done by inserting a suitable screwdriver tip or blade into the opening in the right-hand front corner of the PCB and carefully lifting the board a little at a time.
g) Locate the three solder spots to the right of the trunking processor IC548 (80C31). The approximate position of the spots is indicated by three solid black squares in the drawing below.



i) Again locate the three solder spots, this time at the solder side of the PCB.
j) The centre spot is connected to ground via a short PCB track. Break this track by cutting it with a sharp hobby knife or a PCB drill. Use an ohmmeter to check that the connection between the two spots is really gone forever. Do not rely on your eyesight! Wipe and blow the PCB surface clean of copper debris.
k) Solder a thin piece of wire (1 strand is enough) between the centre spot and the ‘other ’ spot (+5V).
l) Inspect your work with a magnifying glass to make sure no short-circuit has been installed! Remember: make an error here = your own fault = control board destroyed = a lot of trouble.
m) Put the PCB back in position, push-fit the connectors at the front edge, then secure the screws.
n) Remove the AT27C512 firmware PROM (IC308, it usually has a sticker on it) and replace it with the 27C512 EPROM programmed with the new firmware from the File Downloads page. The notch in the EPROM is at the side of the PCB edge.
o) Remove the EEPROM type 24C16 and re-program it with the file from the File Downloads page. Re-install the EEPROM in its socket. Note that some EEPROMs have a round hole to mark pin 1, instead of a notch between pins 1 and 8.
p) Mount the console on the radio. The white connector is polarized so cannot be fitted the wrong way around. Turn the console so that the microphone connector is at the same side as the number keys.
q) Finally, check if the BNC socket on the rear of the radio is properly secured. If not, retighten it using a wrench.

FM1200 Testing

Use heavy-duty (min. 2.5mm2 csa) wire for the supply cable, and insert an in-line slow-blow fuse rated at 10A. Connect the microphone, power supply and loudspeaker. If your set came without a connector/cable set, look at the drawing below to find out the pinout of the supply/LSP connector on the rear of the radio (rear view of connector). Pin 8 (Ignition) is usually permanently connected to the positive wire (+12 V).

Set the supply to about 13 volts and switch on the radio using the pushbutton on the front panel. Sometimes the radio produces a short 400Hz tone. The display will indicate the loudspeaker symbol in the top left-hand corner. To the right, you will see the start-up frequency and below it the associated channel number. Current consumption at this point should be less than 600mA with the LCD backlight turned on. If you get ‘Undefined Error Code 03’ then the radio will contain no or incorrect user data in the EEPROM. 

First connect a dummy-load and then key the transmitter. RF power should be in excess of 25 watts (I measured 28 watts on a Bird Thruline, and 26 watts on a Marconi TH1035).

FM1200 additional information

The program and data in the EPROM installed on the control board originate from the FM1100, the 'non-trunking' sibling of the FM1200. The program and data in the display head EPROM were developed out of an example taken from an FM1100. Mind you, the frequencies and texts that appear on the LCD are held in the console EPROM, not (unfortunately) in the EEPROM! The process of display text customization is explained here.

All radios from the FM1000 series look identical and are, in principle, produced for any PMR band between 50MHz and 550MHz. So be sure to read and understand the type number! The STM22 is a hit for 70cm amateur use. When purchasing an unknown ‘FM1000’ radio, make sure you are aware of the number/letter combination indicating the frequency band, bandwidth and transmitter power. The FM1200 SK111 seems to be around in vast quantities (ex trunking systems in Band 3) but it requires major hardware surgery because of its unusual frequency range (K1 band = 175 to 208MHz).

The transparent film you will have found on the LCD is, of course, intended for the original application of the radio. Using the original film, a graphics program, a laser printer and some transparent sheet it is easy to make a new film with the appropriate legends on it. An ordinary copy machine is also suitable, although professionals will of course have nothing less than real acetate film. In the table on the File Downloads page I've included film designs for the FM1100 and FM1200.

Loading a different set of frequencies is only possible if you have rather special equipment available capable of directly writing into the EEPROM using a prescribed format. This equipment is called PDP (Portable Data Programmer) or CDP (Computer Data Programmer). As part of my collection of vintage Philips PMR stuff I happen to have a PDP Level 3 and a Factory Level CDP (FDP7).


Because the modification was designed to be as simple as possible, the radio is pretty Spartan when it comes to the user interface. Do remember however that the FM1200, like many other ex PMR equipment, was never designed to act as an amateur radio transceiver. None the less, an FM1200 converted according to this recipe should be perfect as a simple mobile rig for a couple of fixed channels or a local 70cm repeater station. The quality of the modulation has been judged as 'excellent' throughout.

The converted FM1200 is simple to operate. Press the CH(annel) key and enter the channel number. The associated frequency will appear instantly on the display. You can start transmitting straight away by pressing the red PTT button on the microphone. The knobs for 'squelch defeat' and 'low power' will be used less often.

The channel/frequency allocation for UK, Dutch (NL), German (DL) and Finnish (SF) radio amateurs is given as a an Excel spreadsheet on the File Downloads page. The first two dozen or so channels are reserved for 70cm repeaters. Unfortunately the FM1200 does not have an internal 1750 Hz call tone generator, 5-tone calling or CTCSS, so that you have to add these options your self using suitable hardware. Fortunately, the microphone has enough space to allow a miniature 1750Hz tone call board to be fitted.

The FM1100

After this fairly extensive description of the FM1200 I can be brief about the FM1100. Make sure you get the subtype RA911 (20 kHz channel spacing), VA911(25kHz) or SA911 (12.5 kHz). The FM1100 only requires the two EPROMs and one EEPROM to be replaced to turn it into a 25-watt 2m band transceiver with 100 channels between 144.5000 and 145.9250 MHz.

As opposed to the FM1200, the FM1110 does contain the required ICs for 1750 Hz tone calling, variable 5-tone calling to various standards and even variable CTCSS (TX-Only). The latter option is however only possible after a small hardware modification to the control board.

 The result of this conversion job (well, exchanging three ICs) is a robust transceiver. Operating the FM1100 is largely identical to the FM1200, but with 5-tone calling and CTCSS added. Press the * button and then enter the 5-digit code you want to transmit. The tone sequence is sent by pressing the red button. The same for the CTCSS: first press SETUP, then select the desired subtone (for example, code 02 = 71.9 Hz). Enable CTCSS by pressing the CTCSS button. The selected subtone will be transmitted along with your speech signal on the current channel. If CTCSS is switched on, the receiver will be blocked for all incoming signals not containing the selected subtone. A 1750 Hz tone is transmitted for about 1.5 seconds by pressing the grey key on the microphone.



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Last modified: februari 15, 2002