This a pretty old rig, sold by PYE and PHILIPS. AUTOPHON also sold it under the model SE-156. But in fact, the main board was made by PYE. But the front panel is different. So at first glance, the two transceiver seems different.
The MX-294 is a VHF type, and the MX-296 is for the UHF band.
I modified two of them. The MX-294 beeing now running at a local APRS digi, I have no pics of it available!
So I will show you the UHF one.
This was a 16 Chanel Rig, but I augmented the channel number to 64, by adding 2 switches.
The modification was made using the very good book of G4HLC, Chris Lorek
PMR Conversion Handbook (ISBN 1-872309-40-2), published by the RSGB
Pages 38 to 55 explain all what you need, in order to modify an MX294 (VHF) or an MX296 (UHF)
An other interesting sorurce of information is the web site from Atlanta Communications, devoted to PMR conversion, especially the MX 290 serie from PYE!
A last link, before beginning to work, is the schematics of the MX-294, on F5JTZ's websiteSo I wont' repeat all the stuff. Here are just some pictures of my work:
View of the front panel. You can see the two swiches that I added (gray), in order to get 64 channels.
The potentiometer (white) for the squelch, and the 1750 Hz button (red) are also "new".
Here is a view inside the transceiver
And a detailed look at the "new" circuit board, where I put the reprogrammable (UV) EPROM and the 1750 Hz generator (based on a NE 555)
Finally a picture of the backside of the front panel. The metal can contains the TX and the RX VCOs (Voltage Controlled Oscillators)
Last but not least, here is an EXCEL file that you can use to generate your own EPROM Files. It implements the algorithm explained in G4HCL's book. You will need to activate the macros. You can also download directly the EPROM binary file, but you won't be able to choose the frequencies you want, out of the ones that are provided.
I also transformed a second Transceiver of the same model, in order to run a local APRS digipeater. I confess that the case is very "primitive". Anyway it ran very well for more than one year now. The easy thing with mono-frequency radios is that they are easyer to tune (no problem at ends of the band, no VCO/PLL lock range problem,...), you don't need a channel selector, nor a display to know where you are transmitting!
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