PFX HRU with extended case.
Front view of PF85 (top) and PFX (bottom) with antennas removed.
Newcomers to the PFX are advised to download and read Section 1 of the Service Manual (TP312).
The PF85 and its successor the PFX are often confused. The PF85 is a 3-channel crystal-controlled handheld, while the PFX is a 16-, 32- or 100-channel handheld with synthesizer control. The letters PF stand for PocketFone, a highly successful series of handhelds designed and marketed by Pye before Philips took over.
The PF85 is hardly worth buying these days because the cost of crystals made to order will almost certainly exceed that of the radio itself.
Like many other PMRs from Philips Telecommunications, the PFX comes in a staggering number of variants, not all of which are of interest to radio amateurs. As always the clues are to be taken from the type label at the back of the radio.
One fault that occurs with many ex-service PFX's is apparent from the fact that the radio indicates Channel 00 on alternate lines of the LCD and effectively works on Channel 1 only. The cure is simply to replace the internal 3-volt Lithium button cells and all will be restored to its former glory.
Type code analysis
The label on the back of the PFX will tell a lot, but not all, about the radio. The codes used largely follow the Philips PMR tradition. Unfortunately, it is difficult to determine the exact band the radio works in, e.g., A1 or A2, because the print on the label will only give 'A'. However the existing PMR channel(s) loaded in the radio will provide a useful clue. The commonly found PFX A(2) band radio will not be pulled down to 2 metres. Another popular model, the PFX U(P), will cover our 70cms band but with a increasing deafness towards 430 MHz. All PFX radios require VCO and RF front-end retuning after any frequency change of more than about 2 MHz.
If you need to be absolutely sure about the band your PFX was designed for, there is no alternative to opening the radio, copy the (hand-pencilled!) production number on a couple of conspicuous modules and then find the matching identifiers in the tables that can be downloaded here.
PFX PROMsThe PFX takes its frequency information from a PROM (programmable read-only memory) chip type 82S129 (16-channel), 82S131 (32-channel) or 82S185 (100-channel). These 4-bit PROMs are products of the early 1980's which unfortunately means that they are now obsolete and very hard to get. The younger generation may be surprised to learn that a PROM can not be erased and re-programmed. However, if you are lucky, the PROM in your PFX may have unused space to accommodate your channel codes. In a PROM, an empty location reads 0, not F as in an EPROM.
PFX Programming SoftwareThe algorithm used to build the code words that determine the receive and transmit frequencies in the PFX are interesting in themselves. However you do not need to know them if you have suitable software available that turns the desired TX/RX channel frequencies into codes and then puts them in sequence to build a file that can be blown into a PROM.
This little program, FPROM for PFX and MX290, does it all. Here are my notes to advanced users.
Here's what FPROM looks like. Impressive menu structure, eh?
to be published...
The Philips Mobile Radio Collection currently has the following PF and PFX radios, accessories and documentation:
For more information on PFX series PMRs from Philips/Pye, join the newsgroup 'PFX' via www.yahoogroups.com/group/PFX.
Last modified: February 21, 2002