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Racal PRM-4515   Cougar
Secure handheld radio

The PRM-4515 is a military hand-held radio with (optional) 16 kbit/sec digital voice encryption, developed by Racal Tacticom Ltd.1 in Reading (UK) in the late 1980s for use by Special Forces (SF) and for covert (police) operations. It is known in the US as PRC-6515 and can (optionally) be fitted with a VINSON (KY-57) compatible crypto module, in which case it is known as AN/CSZ-6.
Different versions of the radio were available, mainly for different frequency bands, each with 10 programmable channels, 2 Watt output and clear speech (CLR) with 150 Hz CTCSS 2 . If the optional crypto unit is fitted, the device offers high-end digital encryption on 16 kbit/sec CVSD voice data 3 . Two crypto keys (A and B) can be stored simultaneously and a ZEROIZE facility is available to purge the keys when compromised.

The device shown here is a PRM-4515L with crypto facilities, and is dated 1 December 1987. It is shown here without the helical antenna.
Racal PRM-4515L

In order to operate the PRM4515, a microphone/speaker, an antenna and a battery are needed as a bare minimum. In addition, a wide range of accessories is available, allowing the PRM-4515 to be adapted for various applications, including covert operations, surveillance, VIP protection, etc. For mobile and stationary use, the PRM-4515 was placed in a special cradle, known as the SMT.

The Racal Cougar system (COUGARNET) was used in various countries, including the US, the UK, India, The Netherlands and Belgium. For covert operations, the compatible, but more compact, PRM-4735 was sometimes used as it can be hidden under the operator's clothing more easily. The PRM-4515 is crypto-compatible with the external MA-4777 voice encryption unit, so that other non-Cougar radiosets can be used securely in a Cougar configuration or COUGARNET.
  1. Racal was taken over by Thales in 2000.
  2. CTCSS = Continuous Tone Coded Squelch System.
  3. CVSD = Continuous Variable Slope Delta modulation.

Racal PRM-4515L PRM-4515L Cougar hand-held radio PRM-4515L with battery Front panel Side panel Microphone/speaker MA-4730A ECU TA-4523 with PRM-4515

As the PRM-4515 is a tactical radio, the number of controls has been kept to a minimum in order to avoid operator mistakes. Furthermore the radio is designed in such a way that the controls are easily accessible when the operator wears gloves. The battery is attached at the rear, whilst the on/off switch is at the center of the front panel. This switch is also used to adjust the volume.

Two further controls are available at the side panel. The one closest to the front panel is the channel selector (1-10). The other one is the MODE selector. It offers a choice between clear speech (CLR) and one of two encryption keys (A or B). It is also used to ZEROIZE the keys.

A suitable antenna should be connected to the TNC socket at the front panel. When used as a hand-held radio, a rubber helical antenna would normally be used. When used in a mobile or stationary environment, using the SMT option, an external antenna should be connected.

The PRM-4515 does not have a built-in microphone and/or speaker, So, in its basic setup, an external speaker/mike combination should be connected to the 7-way 105 socket at the front panel. This socket is also used for the programming device.
Front panel Attaching the battery Front panel Adjusting the volume MODE and Channel selectors Selecting the desired channel Selecting the desired MODE ZEROIZING

The following versions of the PRM-4515 were available:
  • PRM-4515L
    This version offers 10 channels in the lower VHF band (68-88 MHz) also known as the VHF-L band. It offers clear speech (CLR) and (optionally) 2 cryptographic keys that can be purged with the ZEROIZE facility.

  • PRM-4515N
    Same as PRM-4515L but with additional carrier squelch feature.

  • PRM-4515H
    Same features as the PRM-4515L but suitable for a 20 MHz segment in the VHF-H band (132-174 MHz). The 20 MHz segment may start at any 2 MHz offset.

  • PRM-4515U
    Same featues as the PRM-4515L, but operating in the UHF-L band (380-400 MHz) or UHF-H band (403-471 MHz). In the latter case, any 20 MHz segment may be selected, starting at any 4 MHz offset.

Although in principle all PRM-4515 radios with the same suffix (e.g. L, H or U) are identical, there are some customer-specific variations in labels, type shields and colours. The image below shows three variants of the PRM-4515. Note that the rightmost one (an MOD variant) has red selectors.

Three variants of the same radio

Key loading
In order to use the cryptographic features of the PRM-4515, a so-called cryptographic key, or key, or initialisation vector has to be loaded into the radio first. Without a key, the radio can only be used in clear mode. Keys can be loaded into the PRM-4515 by means of two different devices.
Programmer   MA-4073
Full programming and key loading is possible with the large MA-4073 Programmer, which should be connected to the audio socket of the radio by means of a special so-called Fill Cable.

The image on the right shows the MA-4073 Programmer that can be used for programming up to 10 channel frequencies and 4 crypto keys into the PRM-4515. When transferring data this way, the radio can be powered by the MA-4073 programmer, so the battery of the radio does not have to be installed. Note that only 2 crypto keys can be selected on the radio itself (A and B).

 MA-4073 Programmer
Racal MA-4073 data transfer device

Fill Gun   MA-4083
As an alternative, the much smaller MA-4083 Fill Gun can be used, but only for one type of data at a time (frequencies or crypto keys). The Fill Gun itself is loaded by the MA-4073 Programmer.

Note that when using the MA-4083 fill gun to load data into the PRM-4515, the battery of the radio must be fitted, as it is needed to feed the fill gun.

 MA-4083 Fill Gun
MA-4083G fill gun
DS-102 interface   MA-4778
If the PRM-4515 was issued with the special VINSON/SAVILLE encryption module, a DS-102 compatible key loader had to be used. However, as the fill interface of the PRM-4515 is not compatible with DS-102, the special MA-4778 interface was developed.

The image on the right shows the MA-4778, which has a fixed cable for connection to the PRM-4515 or a compatible radio. The MA-4778 itself has to be filled from a DS102 compatible key loader first, such as the KYK-13.

 More information
Racal MA-4778 key loader with DS-102 protocol

Most devices with high-end encryption are so-called Controlled Cryptographic Items (CCI). In order to prevent a working crypto device from falling into enemy hands, a CCI commonly has a facility to delete the crypto keys in case of an emergency. This facility should be two-fold.

On the PRM-4515, the user has to press the ZEROIZE button whilst simultaneously turning the MODE selector to the 'Z' position. This can be done with one hand, as shown in the image on the right.

Racal MA-4073 data transfer device Racal MA-4083C fill gun Racal MA-4778 key loader with DS-102 protocol ZEROIZING

The following accessories for the MA-4515 are available:
Microphone/speaker combination Helical antenna MA-4516A battery TA-4523 Static, Mobile, Transportable (SMT) unit
MA-4730A External Control Unit (ECU)
Covert wireless microphone and speaker
Optional crypto unit to be plugged into the crypto board Crypto Fill Cable

As the PRM-4515 does not have a built-in microphone and or speaker, an external handset, headset or covert set has to be used.

The image on the right shows the standard microphone speaker that comes with a long cable with a 7-pin 105 connector at the end. It can be connected directly to the 105 socket on the front panel of the PRM-4515 or, when the SMT is used, to the front panel of the SMT.

Battery   MA-4516A
For portable (hand-held) use, the MA-4516A battery should be attached at the bottom of the PRM-4515. The twist-lock mechanism allows the battery to be replaced quickly without the danger of becoming detached in combat.

A slide-lock at the side of the radio has to be released before the battery can be removed.
MA-4516A Battery

Battery   MA-4516B
As an alternative to the standard battery shown above, a slightly longer variant was available that accepted 8 standard 1.5V AA-size cells. This enabled the PRM-4515 to be used in areas where no provisions were available to recharge the batteries whilst the radio was used for an extended period of time.

This type of battery is ideally suited for operating the PRM-4515 today, as most (if not all) existing MA-4515A batteries are dead by now and can no longer be recharged.
Using standard commercial batteries

When used as a handheld radio, the PRM-4515 was usually equipped with a helical antenna that was tuned for the frequency band in which the radio was operated. The image on the right shows an 80MHz version that was used with the VHF-L version of the PRM-4515. The VHF-H and UHF versions are much shorter.

The antenna is connected to the TNC socket on the radio's front panel. When the PRM-4515 was used in a mobile or stationary configuration, an external antenna was generally used.
VHF-L antenna

Microphone/speaker MA-4516B large battery unit MA-4516B large battery unit Opening the battery unit Using standard commercial batteries VHF-L antenna

SMT   TA-4523
When using the PRM-4515 in a desktop or mobile environment, it could be installed in the optional SMT unit (Static/Mobile/Transportable) TA-4523, as shown in the image on the right.

The TA-4523 contains a 20W amplifier and connects only to the antenna and audio sockets of the PRM-4515. Power is supplied to the radio via the 7-way 105 audio socket. Available in L, H en U versions.
TA-4523 with PRM-4515

ECU   MA-4730
When the PRM-4515 was used in a mobile setup, it was possible to install the radio with the TA-4523 SMT in, say, the trunk of a car, whilst the controls were located at the dash­board.

For this purpose the MA-4730 External Control Unit (ECU) was available. It connects to the microphone socket of the TA-4523, whilst the microphone is moved to the ECU.
MA-4730A ECU

Covert use
For covert operations, surveillance task and observations, special covert accessories were available, such as a body harness, wire antennas, wireless earpieces (neck loop), etc.

The image on the right shows some examples of such accessories. For a more complete overview, please refer to the description of the PRM-4735 covert radio.
Inductor/microphone with wireless earpiece

Fill cable   ST 792252
In order to load channel frequencies and cryptographic keys into the PRM-4515, a special FILL cable, such as the one shown here, is used.

The cable should be connected between the AUDIO socket of the PRM-4515 and the FILL socket of the MA-4073 Programmer or the MA-4083 Fill Gun.
ST-792252 Fill cable for PRM-4515

The PRM-4515 is a well-built compact ruggedized handheld radio, that measures 30 x 75 x 150 mm (213 mm with MA-4516A battery) and weights approx. 450 g (800 g with battery). The radio is housed in a die-case aluminium case that consists of a frame with full-size panels at the top and the bottom. The interior is accessible from both sides by removing these two panels.
Inside the aluminium frame are three large PCBs. At the centre is the Control Board that holds the microcontroller, the memory and the user interface. It acts as a carrier for the other two boards. At the top side (the side that holds the serial number) is the transceiver board. The bottom side holds the crypto board.

The image on the right shows the interior of a PRM-4515L of which the bottom panel has been removed. The large PCB that is exposed, is the Crypto Board. It can be removed by releasing 4 bolts after which it can be pulled upwards.
Interior: crypto board

It is connected to the Control Board via a 32-pin header, and a short piece of black string is provided to pull out the board easily. The crypto board itself is identical for all crypto enabled devices but contains a smaller daughter card or crypto unit that holds the actual crypto heart, so that it can be customized. Different crypto units were supplied to different countries/customers.
For the UK government, a special version was used with a secret CESG-developed algorithm. In the same vain, an NSA-developed algorithm was supplied to US Government users. For other customers and nations, a third variant with a Racal proprietary algorithm was available.

The image on the right shows the MA4437 crypto unit that is mounted in a socket at the edge of the crypto board. It can be easily be swapped for another version. The crypto board has a small blue Lithium battery in one corner that is used for maintaining the crypto keys.
Crypto unit

The reverse side of the crypto board contains all SMD components. It consists of the 16 kbit/sec CVSD modulator/demodulator (modem), clock recovery circuit, etc. The circuit diagram of the crypto board is largely identical to the crypto board inside the MA-4777 voice encryption unit.
The crypto board is fully controlled and driven by the Control Board that is mounted at the center of the die-cast aluminium body of the PRM-4515. It contains a large 40-pin custom microprocessor plus the voltage regulators that provide power to the various parts of the radio.

All external controls and connections are connected to the control board via short flex PCBs, as is clearly visible in the image on the right. The reverse side of this PCB holds the SMD components. The control board also contains the squelch system and the LF audio amplifier.
Close-up of the control board

The reverse side of the control board also carries the transceiver PCB which is mounted at the top side of the radio. The transceiver is connected to the control board via a 20 way header and is held in place by 4 bolts. After removing these 4 bolts, the transceiver PCB can be pulled out.
Like the crypto board, the transceiver board has a short piece of black string that allows the transceiver to be extracted from the control board without damaging the header. Apart from the 2- way header, the transceiver board is also connected to the antenna socket at the radio's front panel by means of an SMB connector.

This board contains the frequency synthesizer, the receiver, the modulator and the transmitter. The receiver has a 1st IF of 21.4 MHz and a 2nd IF of 455 kHz. In the transmitter, clear audio is modulated directly onto the reference oscillator.
Interior: transceiver board removed

The large metal can at the top left of the transceiver board, contains the transmitter's Power Amplifier (PA) that produces approx. 2W output. A small Low Pass Filter (LPF) is mounted between the PA and the antenna socket in order to filter any harmonic signals from the output signal.
Top and bottom panel removed Interior: crypto board Removing the crypto board Crypto board removed Crypto board top side Crypto board bottom side Crypto unit Crypto unit
Interior (without crypto board) Close-up of the control board Control board top view Control board bottom view Interior: transceiver board removed Transceiver board Transceiver board (bottom view) Transmitter board removed but still connected to the antenna sockete

Crypto modules
For secure communication, the PRM-4515 could be enhanced with a voice encryption/decryption module (or Crypto Module, or Crypto Unit), that was installed on the Crypto Board. Various types of crypto modules were available for different customers and different needs. Note that each type requires a different version of the MA-4073 Programmer and/or the MA-4083 fill gun.
The standard crypto module that was delivered to most customers, is the MA-4437 shown in the image on the right. It uses a Racal-proprietary cryptographic algorithm and can hold up to four cryptographic keys, each of which consists of 120 bits. The key is constructed in the MA-4073 Programmer from 36 octal digits (0-7, or 3 bits) plus a 12-bit fixed prefix (all '1's by default).

The crypto module can encrypt or decrypt the radio's digital 16 kb/s CVSD modulated data stream, but not both at the same time. That means that it can only be used in simplex mode.
MA-4437 top side

The keys are stored inside a Harris MH-6504-9 4096-bit CMOS memory, that is located at the upper side of the module. When using this module, the keys are retained by a built-in battery for more than 3 years, even when the radio is disconnected from the power [1]. This is known as long crypto retention. The presence of a crypto module causes a 128 ms delay in the audio path, which is needed for crypto processing. At the start of a transmission is a 96 ms preamble. Although 4 keys can be stored on the MA-4437, only two of them can be used by the PRM-4515.
This is a different module that was supplied to some European customers. It is not compatible with the MA-4437 and requires a different version of the programmer and the fill gun ('G' instead of 'C'-version). Nevertheless, the key length seems to be identical (120 bits) [3].

MA-4487 boards are generally red, whilst MA-4437 boards are green. Although it is possible that this board contains the SAVILLE encryption algorithm, but it is more likely that it is 'just' a variation of the standard MA-4437 module. Like the MA-4437 is sends a 96 ms preamble.
MA-4487 top side

The layout of the MA-4487 board is identical to that of the MA-4437 and the 4 chips are also similar, except for the fact that the product code of the two large chips (one at the top and one at the bottom) have a C-suffix (MT70083C versus MT70083, and MT70084C versus MT70084). Like the MA-4437, this board can hold up to 4 crypto keys, but only two of them can be selected.
VINSON   Special module
For selected US-approved customers, a so-called Special Module was available that contained the secret SAVILLE encryption algorithm developed by GCHQ and the NSA. This offered compatibility with VINSON equipment like the American KY-57 and the British BID/250 Lamberton voice ciphers.

As SAVILLE uses a 128-bit key (120 key bits plus an 8-bit checksum), the standard MA-4073 and MA-4083 key fillers can not be used. Instead, the keys were transferred by means of a DS-102 fill gun, such as the KYK-13, in combination with the special Racal MA-4778 key fill interface.
MA-4437 top side

When using this module, only two crypto keys can be stored in the device. Furthermore, the crypto keys are only retained for a minimum of 15 minutes (typically several hours) when the device is disconnected from its power source. This principle is known as short crypto retention.

Help required - So far we have never seen the VINSON compatible module, although it is mentioned in official sales information [2] and the required key loaders have been found. If you have any additional information about this mysterious module, please contact us.
No crypto
When the radio is used without a crypto module, four wire loops have to be inserted in the socket the normally contains the crypto module. These wire loops ensure that the 16 kb/s CVSD data is properly bypassed.

The drawing on the right shows the position of the four wire links, as seen from the top. Note the position of the notch, which is close to the edge of the PCB.

Analogue encryption   MA-4258
Apart from the digital encryption options listed above, Racal also offered the MA-4258 analogue encryption board, which provided time and frequency domain voice scrambling. So far we have never seen this module and it is quite possible that it was never sold, given the limited security offered by voice scramblers in comparison to digital encryption. If you have more information about this module, please contact us.
Crypto retention
When the main battery of the PRM-4735 is disconnected, the crypto keys are retained for at least 15 minutes (typically several hours), to ensure that the batteries can be swapped without loosing the keys. Normally, a large capacitor (known as a 'SuperCap') on the control board ensures that sufficient power is supplied to the crypto module during this period. In Racal terminology, this is known as short crypto retention. It was typically used in combination with the VINSON module.

Depending on the requirements of the customer, a Lithium battery could be installed in place of the SuperCap, to ensure that the keys were retained indefinitely (typically more than 3 years) when the main battery was disconnected. This is known as long crypto retention. Although it was typically used with the MA-4437, any combination of retention/crypto module was possible.
MA-4437 top side MA-4437 bottom side MA-4437 top side MA-4437 bottom side MA-4487 top side MA-4487 bottom side MA-4487 top side MA-4487 bottom side

Compatible equipment
All crypto modules have the same footprint and can be installed in any PRM-4735. They are also used in other Racal crypto-capable products, such as the PRM-4515 and the MA-4777. A full list of compatible products is given below. Note that devices are only inter­operable if they use the same crypto algorithm, the same frequencies and the same keys. Please note that the devices marked with a * do not use a Racal crypto module, but a proprietary VINSON compatible module, that is interoperable with a Racal device that has the mysterious VINSON module installed.
Racal PRM-4735 Cougar covert radio with voice encryption Thales PRM-5120 Cougar covert radio with voice encryption Racal MA-4777 Digital voice encryptor KY-57 VINSON voice encryptor (USA) KY-99 voice and data encryptor (USA) in VINSON mode UK Lamberton (BID/250)
*) Only if the PRM-4735 is fitted with a VINSON-compatible crypto module.

 Other Cougar equipment

The audio connector at the front panel of the PRM-4515 is a a female Clansman-style 105 socket that is wired according to the Clansman standard. The same layout is used for the audio sockets on the TA-4523 SMT and the MA-4730 ECU. The socket is wired as follows:
  1. Mic or Fixed Level Audio (FLA) or program input
  2. Mic return or Wideband programming
  3. 10V Power in or out (current out ≤ 100 mA)
  4. Audio/Data
  5. Ground
  6. PTT or 4 kb/s data or key fill data
  7. Squelch or CTS
The PRM-4515 is known to be used in the following countries:
  • UK Army (PRM4515H)
  • UK Navy, Royal Marines, Military Police (PRM4515L and N)
  • UK MOD (PRM-4515U)
  • UK Police (PRM-4515H and PRM-4735H)
  • US Airforce (PRC-6515/H)
  • India, security forces
  • Sri Lanka, Navy
  • Netherlands, Police (PRM-4515L and PRM-4735L)
  • Netherlands, MOD (PRM-4515L)
  • Belgium, Police (PRM-4515L)
  1. Racal Cougar Personal PRM 4515, leaflet
    Publication No. 2467-4. June 1989.

  2. Racal, MA 4437 Digital Voice Encryption Module
    Leaflet. Date unknown. Retrieved May 2014. 1

  3. Racal, Static/Mobile/Transportable system SRM 4515, leaflet
    Publication No. 2469-5. November 1990.

  4. Racal, battery charger - MA 4529A, leaflet
    Publication No. 2469-5. November 1990.

  5. Racal Tacticom Ltd., VHF (Low Band) Transceiver PRM-4515L Technical Manual
    TH 8087/L, issue 6. January 1996.

  6. Racal Tacticom Ltd., VHF (Low Band) Amplifier TA-4523L Technical Manual
    TH 8088, issue 2. January 1996.

  7. Racal Tacticom Ltd., UHF Transceiver PRM-4515U Technical Manual
    TH 7158. Issue 1, December 1986. 1

  1. Document kindly supplied by Dave McKay, PRM Conversion List (website) [1].

  1. Dave McKay (G1JWG), Racal Cougar and Cougarnet Radio System
    Retrieved May 2014.

  2. Jane's Military Communications, AN/CSZ-6 Vinson-compatible Hand-held Transceiver
    Fifteenth Edition 1994-1995. p. 551.

  3. Racal Radio Ltd., MA 4073C and MA 4073G Programmer, User Handbook
    Ref. RH 8224. Issue 3. Date unknown.

Further information

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