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PFX-PM (UP 2093)
Portable Radio with Digital Encryption

The Philips PFX-PM was a portable half-duplex radio with digital encryption. It was based on a PFX radio, built by Philips Radio Communication Systems (RCS, formerly: Pye) in Cambridge (UK). In 1990, Philips Usfa developed the UP 2093 half-duplex crypto module that fitted in the lower part of the extended version of the PFX radio. Differt versions of the crypto-module were made.

The image on the right shows the extended version of the PFX-PM, with detached battery. It is longer than the standard version. The small instruction booklet (TP1962) is also shown here. Two basic versions of this radio exist: one for the 2-meter band (150 MHz) and one for the 70-cm band (400 MHz). The 2-meter version was available in various frequency ranges.

The radio shown here is of the type PFXPM LVA, which means it's a low-power version (L) with 25 kHz channel spacing (V) and a frequency range of 148-162 MHz or 160-174 MHz (A).
Philips PFX-PM with detached battery and manual

The exact details of this PFX radio can be found on Jan Buiting's website about his Philips Mobile and Portable radio Collection. Please note that the frequency range is either 148-162 MHz (A1) or 160-174 MHz (A2) but not both. One can only tell the difference by opening the unit.

The reason for using 25 kHz channel spacing rather than 12.5 kHz, is that digital delta modulation is used for the transmission of voice data. This requires a bandwidth of at least 16 kHz in order to obtain a good voice quality.

PFX-PM radio, battery and instruction booklet radio with separated battery Close-up of the radio's front panel

Crypto Module
The entire crypto unit consists of three stacked PCBs plus a sealed Crypto Module developed and manufactured by Philips Usfa. By fitting components on both sides of each PCB, they managed to fit the complete assembly in the CTCSS compartment of the extended version of the PFX.

The three stacked PCBs contain the AD converter, Delta Modulator, the DA converter, additional audio circuits and some glue logic.

The actual encryption and decryption of the data takes place in the sealed UP 2093 crypto module shown in the image on the right. The crypto module itself consists of a PCB with components on both sides (see below).

The image on the right shows the complete stack of three PCBs with the crypto-module on top. At the front is the 3V lithium battery.
Complete assembly of the interface with the crypto-module on top.

The top part of the crypto module cannot be opened as it is sealed in some kind of very tough foam than can't be removed without damaging the components. The rather unique photographs below, show the interior of the crypto-module. this prototype was used during the development.

The crypto-module is in fact a PCB with four chips at the top surface. At the top right is the custom-made OQ4434 crypto-chip (ASIC) with its typical golden top cover. The image on the right also shows a couple of bare OA4434 chips, one of which is missing its golden roof.

At the top left is a one-time programmable Intel 87C51 microcontroller that contains the control firmware. At the front are two Programmable Array Logic ICs (PALs). The other side of the PCB (bottom) contains the buffers and the glue logic to interface to the rest of the radio.
The crypto-module of the PFX-PM (left). At the right the interior of the module. At the front the bare crypto-chips.

Complete assembly of the interface with the crypto-module on top. The crypto-module of the PFX-PM (left). At the right the interior of the module. At the front the bare crypto-chips. Crypto-module, top view Crypto-module bottom view PFX-PM crypto-interface, consisting of three sandwiched boards. Placing the module View at the crypto extension unit after removing the radio's back panel The delta modulation unit consisting of 3 stacked PCBs

Loading the crypto keys
With every crypto system, the creation and distribution of the key(s) requires special attention and security measures. The PFX-PM is no exception to this rule. Philips RCS created a special programming kit for the creation and distribution of up to four different keys.

The kit consisted of a software package that converted a standard PC (DOS) into a Master Key Programmer (MPK). With the software, the person responsible for the key generation could manually enter 4 different keys in hexadecimal format. The software could also generate random keys.

Once generated, the Slave Key Programmer (SKP) would be used to transfer the key material to the various PFX-PM radios (keyfiller). The image on the right shows an SKP connected to a PFX-PM radio with a special transfer cable.

The SKP (right) is housed in the case of a PFX radio. Please note that both the radio and the SKP should be powered by their own batteries (not shown here). The special transfer cable has identical connectors at both ends, allowing it to connect to the accessory socket of the radio. The SKP could also be used to transfer the keys to further SKPs.

The SKP has two buttons. One on top of the unit (test) and one on the side for starting the transfer (the former PTT button). The speaker of the SKP is used for communication with the user. A single beep indicates an error, whilst a double beep is sounded after a successful transfer of key material.

A low-battery condition is indicated by three short clicks on the speaker of the SKP. Changing the battery should take less then one minute in order not to lose the key material stored in the SKP's memory. The SKP cannot be turned off and will always consume a little bit of power in order to retain the keys.

Please note that the PFX-PM allows 8 crypto keys to be programmed, whilst the SKP software only allows 4 different keys to be set. This is because a longer 5th key is permanently set by the software (hard-coded), allowing secure communication even when the keys are lost.

Slave Key Programmer (SKP) connected to the PFX-PM Close-up of the programming connector on the PFX-PM Close-up of the test button of the SKP Programming cable Close-up of the programming cable PC connection cable for the Master Key Programmer (MKP) Close-up of the PC connection cable PC software (DOS) for the Master Key Programmer (MKP)

  1. Philips RCS, PFX-PM Portable Radio with Digital Encryption, Operating Instructions
    TP1962, 1 November 1989

  2. Philips RCS, Master Key Generator and Programmer (MKP) for PFX-PM, User Manual
    TP875, 1990

  3. Philips RCS, Slave Key Programmer (SKP), User Guide
    TP1992 issue 1, 1990

  4. Philips RCS, Philips digital secure speech system
    Brochure with all Philips crypto radio products.
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Crypto Museum. Last changed: Friday, 19 August 2011 - 09:36 CET.
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