There seems to be a dearth of information on the Internet on the subject of the FX5000. This struck me as rather odd, considering their flexibility, reliability and increasing availability.

Nowhere could I find any guidance on the subject of programming these radios onto 2 metre Amateur frequencies - or any other frequency for that matter. One website offered a programming tool for UHF FX5000's but this turned out to be a false ray of hope. Following their link allowed me to download the programming software for the Philips PR710. Since the PR710 is a handheld radio, this software proved to be of little use, and besides, I already had a copy of that program!!

So, I set about the task of finding out how to do it for myself.

I hope that the results of my efforts will be of use to others who would like to use a 'B'-Band FX5000 for their next repeater project.

Since this a technical article, it will probably appear rather dull to people looking for glitzy web pages with lots of fancy stuff. Regardless of how dull it may be, I would have been eternally grateful to anyone who had already presented this information for the benefit of others. Hopefully, if you find yourself in the same position as I did - short of help - you will be grateful for what follows and ignore the lack of style!

The Synthesiser
The FX5000 uses the GEC/Plessey NJ8820 synthesiser IC. This device has the means to interface to a PROM or EPROM to retrieve frequency data stored therein. The frequency data takes the form of 8 consecutive bytes which, between them, supply the values for 3 variables known as 'R', 'A' and 'M'. These values are written into internal registers to control the counters which do the work of frequency division. The 'R' counter divides the external reference frequency down to a value which is usually half the channel spacing (e.g. 6.25KHz for a 12.5KHz channel). Notice, though, that the Reference counter is followed by a fixed, divide-by-two, counter. Because of this, our calculations will focus on dividing the reference oscillator by a value of 'R' which results in a frequency equal to the channel spacing.		The 'M' and 'A' counters perform the task of dividing the external VCO frequency. Since the division of the VCO frequency down to, say, 6.25KHz cannot always be achieved using an even number as a divisor, the 'A' register controls a switchable prescaler which, in the case of the receiver, alters the prescale factor from 80 to 81 by means of the Modulus Control output. More on this topic follows.


NJ8820 Data Format

Byte	DS2	DS1	DS0	D3	D2	D1	D0
0	0	0	0	M1	M0
1	0	0	1	M5	M4	M3	M2
2	0	1	0	M9	M8	M7	M6
3	0	1	1	A3	A2	A1	A0
4	1	0	0		A6	A5	A4
5	1	0	1	R3	R2	R1	R0
6	1	1	0	R7	R6	R5	R4
7	1	1	1		R10	R9	R8

The table shows how the bits making up the values of R, A and M are split up between the 8 data bytes required by the synthesiser, when stored in an EPROM. Most notable is the fact that the bits making up the M value are left-shifted by two bits.

FX5000 notes to bear in mind:

General Notes: The EPROM data is split up into two types:- Normal (customer data) and test data. Each of these groups is further split into transmit and receive frequency data. This gives rise to four groups of frequency data, viz: Customer transmit frequency data Customer receive frequency data Test transmit frequency data Test receive frequency data. Mysteriously, the existing EPROM in my FX5000 has no data in the locations that would be appropriate for channel zero. I didn't attempt to reason this out, and simply followed the pattern. Therefore, the first channel data values begin at 0x0008 for the transmitter, and 0x0408 for the receiver (8 bytes per channel, remember).

Transmitter		Receiver
The TX Oscillator runs at Ftx+20MHz. This frequency is fed to the modulation loop, where it is shifted back down to the correct frequency. TX Normal Channels in EPROM address range 0000h to 03F8h TX Test Channels in EPROM address range 2000 to 23F8h Synthesiser prescaler divides by 64 or 65		RX Local Oscillator is at Frx-21.4MHz RX Normal Channels in EPROM address range 0400h to 07F8h RX Test Channels in EPROM address range 2400h to 27F8h Synthesiser prescaler divides by 80 or 81 The data bits between the EPROM and the Synthesiser are reversed on the PCB (must have been easier to lay-out the print that way!)
So, having laid the groundwork, we'll cut to the chase on page 2