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Voice Racal Covert PRM-4735 →
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 with the
original helical antenna present. It is dated 1 December 1987.
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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.
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Racal was taken over by Thales in 2000.
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CTCSS = Continuous Tone Coded Squelch System.
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CVSD = Continuous Variable Slope Delta modulation.
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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.
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The following versions of the PRM-4515 were available:
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- 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.
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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.
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All crypto modules
have the same footprint and can be installed
in any PRM-4515. They are also used in other Racal crypto-capable
products, such as the PRM-4735
and the MA-4777.
A full list of compatible products is given below.
Note that devices are only interoperable if they
use the same algorithm (i.e. the same colour crypto module),
the same frequencies and the same keys.
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VINSON —
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. VINSON uses the highly secret
SAVILLE encryption algorithm
developed by GCHQ and NSA.
➤ More
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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.
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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
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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
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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
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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 is always a two-step action.
On the PRM-4515, the user has to press the ZEROISE 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.
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The following accessories for the MA-4515 are available:
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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The MA-4515 can also be used for secure voice communication, by installing
a crypto module. At least three versions of this crypto module
were available, with a varying degree of security.
The module, and hence its secrecy level, can be recognised by the colour of
the PCB:, which can be red, green or white.
➤ More information
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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VINSON
Special module — wanted item
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When using this module, only two cryptographic 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.
The image above shows a white BID/422/1 module, which is the British
version of VINSON.
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When the radio is used without a crypto module, four
wire loops have to be inserted in the socket that 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.
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Analogue encryption
MA-4258
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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.
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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.
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Racal PRM-4515 units are very suitable for use by Radio Amateurs (HAMs)
with an appropriate radio licence from the authorities. The PRM-4515L
can be made to work in the 70 MHz segment of the VHF-L band,
that has been allocated internationally 1 for HAM use.
Likewise, the 4515H is suitable for the 2 m band (144-146 MHz)
and the 4515U is ideal for 70 cm (430-440 MHz). 2
For Amateurs there is a
great website
that explains many details of the
PRM-4515, complete with socket connections and programming of the channels.
Most of that site is in Dutch, but with help from the clear pictures and
a bit of
Google Translate
you might find what you were looking for.
➤ Page about Racal Cougar on AMATEURTELE.COM
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Before using the radio on these frequencies, check your local regulations.
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Please note that encrypted communications are not allowed on the amateur
radio bands.
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The PRM-4515 is known to have been used in the following countries:
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- 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)
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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:
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- Mic or Fixed Level Audio (FLA) or program input
- Mic return or Wideband programming
- Power in or out +10V (current out ≤ 100 mA)
- Audio/Data (AF out 400mW into 8Ω)
- Ground
- PTT or 4 kb/s data or key fill data
- Squelch or CTS
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- Racal Cougar Personal PRM 4515, leaflet
Publication No. 2467-4. June 1989.
- Racal, MA 4437 Digital Voice Encryption Module
Leaflet. Date unknown. Retrieved May 2014. 1
- Racal, Static/Mobile/Transportable system SRM 4515, leaflet
Publication No. 2469-5. November 1990.
- Racal, battery charger - MA 4529A, leaflet
Publication No. 2469-5. November 1990.
- Racal Tacticom Ltd., VHF (Low Band) Transceiver PRM-4515L Technical Manual
TH 8087/L, issue 6. January 1996.
- Racal Tacticom Ltd., VHF (Low Band) Amplifier TA-4523L Technical Manual
TH 8088, issue 2. January 1996.
- Racal Tacticom Ltd., UHF Transceiver PRM-4515U Technical Manual
TH 7158. Issue 1, December 1986. 1
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Document kindly supplied by Dave McKay, PRM Conversion List (website) [1].
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- Dave McKay (G1JWG), Racal Cougar and Cougarnet Radio System
Retrieved May 2014.
- Jane's Military Communications, AN/CSZ-6 Vinson-compatible Hand-held Transceiver
Fifteenth Edition 1994-1995. p. 551.
- Racal Radio Ltd., MA 4073C and MA 4073G Programmer, User Handbook
Ref. RH 8224. Issue 3. Date unknown.
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© Crypto Museum. Created: Sunday 17 May 2015. Last changed: Wednesday, 19 October 2022 - 06:37 CET.
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