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PFX-PM   UP-2093
Handheld radio with digital encryption

PFX-PM was a handheld half-duplex VHF/UHF FM radio with strong built-in voice encryption, introduced in 1990 by Philips Usfa in Eindhoven (Netherlands). The radio is based on the PFX handheld radio made by Philips Radio Communication Systems (RCS, formerly: Pye) in Cambridge (UK), and is enhanced with a high-end half-duplex encryption module developed by Philips Usfa. The encryption module is also known as UP-2093/xx, with the xx-suffix indicating the version.

In order to accomodate the encryption module, the body of the radio is somewhat longer than that of the standard version. The radio was available in two versions: one for the 2-meter band (150 MHz) and one for the 70-cm band (400 MHz), plus the necessary sub-bands.

The image on the right shows a typical PFX-PM that was made for the 2-meter band. Since it is identified as LVA, it is a low-power variant (L) with 2k kHz channel spacing (V) and a frequency range of 148-162 MHz or 160-174 MHz (A). It is shown here with the TP1962 instruction booklet.
  
Philips PFX-PM with detached battery and manual

Detailed information about the PFX radio is available on Jan Buiting's excellent website about his Philips Mobile and Portable radio Collection [5]. 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.

Also note that the PFX-PM always has a channel spacing of 25 kHz rather than the more common 12.5 MHz. The reason for this is that digital Continuous Variable Slope Delta modulation (CVSD) is used, which 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 Close-up of the radio's front panel Close-up of the radio's front panel
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PFX-PM radio, battery and instruction booklet
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radio with separated battery
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Close-up of the radio's front panel
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Close-up of the radio's front panel
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Close-up of the radio's front panel

Crypto Module
Secure speech is provided by the encryption module, which consists of three stacked PCBs plus a sealed Crypto Module developed by Philips Usfa. By placing components at both sides of each PCB, the encryption unit could be fitted inside the CTCSS 1 compartment of an extended PFX.

The image on the right shows the three stacked circuit boards that form the encryption unit, with the sealed UP-2093 Crypto Module inserted into a socket at the top. At the front corner, the 3V miniature lithium battery is visible. It is used to retain the cryptographic keys in CMOS memory.

The three boards below the Crypto Module hold the DA converter, the CVSD delta modulator, the DA converter, the audio interfaces and some additional 'glue logic'. The actual encryption and decryption takes place inside the UP-2093 unit. Timing is provided by a regular 6.4 MHz crystal.
  
Complete assembly of the interface with the crypto-module on top.

The upper 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 an engineering prototype of the module, revealing what is normally hidden by foam.

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 shown without its golden cover.

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 that interface the unit 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.

  1. CTCSS = Continuous Tone Coded Squelch System.

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

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

The programming kit consisted of a software package that converts a standard PC (DOS) into a Master Key Programmer (MPK). The software allows the person responsible for management of the keys, to create four keys automatically — using a random number generator (RNG) — or to enter them manually in hexadecimal format.

Once the keys are generated, the external Slave Key Programmer (SKP) — shown in the image on the right — was used to transfer the keys to the various PFX-PM radios. The SKP is connected to the PFX-PM radio by means of a special fill 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 at the side.

The SKP could also be used to transfer the keys to further SKPs. It 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 key has successfully been transfered. 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 crypto keys.

Please note that although the PFX-PM has room for 8 crypto keys, the SKP software only allows 4 of them to be altered. This is because a longer 5th key is permanently set by the software (hard-coded), allowing secure communication even when the keys are lost or have become invalid.

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

References
  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.

  5. Jan Buiting, PFX Series
    Website Philips Mobile Radio Collection. Re-retrieved February 2018.
Further information
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Crypto Museum. Created: Saturday 10 March 2012. Last changed: Saturday, 24 February 2018 - 15:40 CET.
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