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MRP-4   Barbara
Radar locator

MRP-4, codenamed Barbara, is a receiver for direction finding of radar stations, manufactured in the early 1970s by Tesla in Czechoslovakia. It is suitable for the reception of pulse transmissions in the 1 - 10 GHz frequency range, and was used during the Cold War for identifying and locating (mobile) radar stations. It can also be used for finding the location of the illumination beam of an externally energized covert listening device (radio bug). Also known as NSN 5840-16-001-1378.
 
The receiver measures 24.5 x 18.5 x 60 cm and weight 3700 grams. It is is constructed in such a way that it can be carried on the chest with the two circular antennas facing forward and the control panel at the top, visible to the operator.

The receiver can detect radio signals between 1 and 10 GHz in its vicinity, and is suitable for the detection of pulse-modulated signals (typically radar), navigation aids and other directional sources, such as point-to-point microwave radio links and bug activation beams. It can also find the pulse repeat frequency of a radar signal.
  
MRP-4

The MRP-4 was first introduced in 1972 and was initially built mainly for the Army of the Soviet Union (USSR). It was also used on tanks and reconnaissance vehicles in Czechoslovakia and other countries of the Warsaw Pact. It was so popular that it was kept in production until 1994. Note however, that from 1989 onwards, Czechoslovakia was no longer part of the Warsaw Pact and that technically the MRP-4 had become a West-European product, complete with NSN number.

But even after Tesla had ceased production of the MRP-4, it was used for many years, probably because it offered good protection against hostile radio signals and because it was relatively easy to operate. According to the maintenance logbook that came with a Polish MRP-4, that unit was re-issued for the Polish mission in Afganistan in 2012 after more than 10 years of storage [A]. In 1995, the MRP-4 was succeeded by the modernized MRP-4M, with extended range to 18 GHz [B].
 
MRP-4 in wooden supply case Inside the transport case MRP-4 with accessories inside carrying bag MRP-4 with accessory box MRP-4 Seen from the rear Bottom view Accessories
Controls
The MRP-4 is designed for operation from the operators chest. A canvas strap should be attached to the two metal rings that are fitted to the unit's body so that the device can be hung from the neck. The diagram below shows the front side of the device that has two circular antennas: a large one for the lower frequencies and a smaller one for the highest frequencies. All controls are located at the narrow top panel, so that they can be accessed easily by the operator. The detector diodes for band I and IV are accessible from the top panel. They are mounted in a special fitting.


The diodes for band II and III are located at the bottom side of the device, as shown above. This image also shows the bay at the rear/bottom for the NiCd battery or the external power adapter. The unit is shown here with the external power adapter installed. The installed part is held in place by a black photo-thread bolt. The interior of the unit can be accessed from the rear panel.
 
Front panel Rear panel Top panel with two antennas Seen from the front MRP-4 Seen from the rear
Power source
The MRP-4 had a range of options for powering the unit. It can be used as a fully self-contained receiver with an internal NiCd battery that lasts several hours, making it ideal for short covert surveillance operations. Alternatively, it can be powered by an external battery pack that lasts several days or even weeks. In addition, it can also be powered by an external 9V DC source.
 
  1. Internal rechargable NiCd battery
  2. Separate portable power pack
  3. External 9V DC source (via adapter)
The internal NiCd battery pack (1) is fitted instead of the external adapter (3). To ensure that it can be recharged under all circumstances, various chargers are supplied with the set. Batteries can be charged from the mains, a 12V car battery or another external source.
 
  1. AC mains charger
  2. DC mobile charger
  3. Combined AC/DC charger (instead of items 1 and 2)
  4. Other power source (via terminal block)

Operation
All controls of the MRP-4 are located at the front panel of the unit. The receiver is constructed in such a way that, when it is carried on the chest (using the neck belt), the controls are facing upwards, whilst the antennas are at the front (facing forward). This gives the operator easy access to the controls when using the receiver for direction finding of an intercepted signal.


The unit is turned ON with the MODE selector at the top right. The desired frequency band is selected with the RANGE selector, whilst the sensitivity is adjusted with the Amplifier knob (between 1 and 12). When operating the device in the dark, the scale illumination button can be pressed to turn the scale lamp on temporarily. When receiving a radar signal, its repeat frequency can be determined by pressing the PO Z button at the top left and rotating the PO knob until the tone frequency is the same. The correct frequency can than be read from the meter scale. Note that for this feature, the MODE selector has to be set to a suitable range: 500, 1000 or 5000 Hz.
 
MODE selector
  • V
    Off
  • B
    Battery check
  • M
    On ?
  • 500
    500 Hz repeat frequency range
  • 1000
    1000 Hz repeat frequency range
  • 5000
    5000 Hz repeat frequency range
Frequency bands
The MRP-4 supports a frequency range from 1 to 10 GHz, divided over 4 bands, marked I, II, III and IV. Note that band I is for the highest frequency band `and band IV is the lowest. Within a band, the receiver is aperiodic, which means that it does not have to be tuned. As a result, the MRP-4 can only be used in close proximity of a transmitter. The bands are divided as follows:
 
  1. 7,000 - 10,000 MHz
  2. 3,300 - 7,000 MHz
  3. 1,900 - 3,200 MHz
  4. 1,000 - 1,800 MHz

 
MRP-4 in use
Cold War
During the Cold War, the MRP-4 was used in many countries of the Warsaw Pact and also in the former Soviet Union (USSR). In the Czechoslovak People's Army (ČSLA) it was issued as part of the standard gear inside the BPzV Svatava 1 reconnaissance vehicle, where it was used for detecting and finding enemy (mobile) radar installations [4]. In the Hungarian Army the MRP-4 was used on pre-strike and post-strike surveillance missions behind enemy lines, by the highly trained and well-equipped Special Reconnaissance Force (SRF), for locating radar sites and C2 2 nodes [5].
 
In the event of a war between East and West, the MRP-4 would have been used to locate fixed ground radar installations and categorize them. It would also have been very effective against the mobile pulse-doppler radar systems used by the Western reconnaissance units, like the Marconi 3 ZB-298 4 shown in the image on the right [6].

The ZB-298 was a static (i.e. non-rotating) pulse doppler radar that worked at ~10 GHz and gave an audible feedback of a moving object. A well-trained operator could recognise the sounds and identify moving men, vehicles, tracks, tanks, etc.
  
Marconi ZB-2987 mobile static doppler radar. Retrieved from [6]. Source unknown.

The ZB-298 also had a visual indicator, constructed from a red laser and a rotating mirror, that allowed distance and size of the moving object to be measured accurately. The image above was probably taken in The Netherlands, as the antenna is labelled PAS OP (watch out). The MRP-4 would have been able to effectively detect, identify and locate this enemy reconnaissance unit.

 More about the ZB-298 radar
 
  1. The BPzV Svatava vehicle was based on the Czechoslovak BVP-1K, which in turn was a copy of the Russian BMP-1 reconnaissance track vehicle.
  2. C2 = Command and Control.
  3. Marconi-Elliot Avionic Systems Ltd, a GEC Marconi Electronics company.
  4. The ZB-298 was known in the UK as Radar GS No. 14.

Afganistan
The MRP-4 was even used in Afganistan as part of the Polish Military Contingent, as late as 2012. Although it is not entirely clear for what purpose it was deployed in Afganistan, it is likely that it was used to detect and locate SHF 1 radio links or mobile (GSM) phones used by the Taliban. For this purpose, old MRP-4 units, that had been in storage for more than 10 years, were re-issued. 2
 
  1. SHF = Super High Frequency.
  2. See deployment status of Polish MRP-4 [A. p14].

Bug finding
Although this hasn't been confirmed, the MRP-4 would have been ideally suited for finding the source of a passive covert listening device, such as The Thing, SATYR or Easy Chair. Bugs of this type are usually activated and powered remotely by a very strong narrow microwave beam that is aimed at the device from a nearby position, typically a few hundred metres from the target.
 
Although suitable microwave detectors were available from the USSR, such as the Osobnjak 8, such detectors could not be used to trace and locate the source of the activation beam.

The antennas of the MRP-4 however, have a very narrow opening angle of 1° - 2°, making it very easy to follow the beam. It could be worn incon­spicuously under the operator's clothing, using just a small earpiece for the acoustic indicator.

 More about bugs
  

 
Countries
The use of the MRP-4 by the following countries has been confirmed:
 
  • Czechoslovakia
  • Hungary
  • Poland
  • USSR

 
Accessories
Wooden transit case Carrying bag
Bag
External loudspeaker Small earpiece Internal rechargable NiCd battery Mains (AC) battery charger
AC
Mobile (DC) battery charger
DC
Universal (AC/DC) battery charger
Battery terminal block External power adapter External power pack Power lead Test unit for simulating radar signals Spare meter (indicator) Tweezers for pulling out the diodes (stored inside the NiCd batteries) Spare detector diodes D608A
Maintenance logbook
Wooden transit case
The MRP-4 was usually supplied in a wooden transit case, complete with a range of spares, supplies, accessories and documentation. The case has four padded compartments in which the various parts are protected during transit.

Inside the top lid of the case is a checklist and a storage plan, so that the user can identify any missing parts and order them if necessary.
  
MRP-4 in wooden supply case

 
Carrying bag
A canvas water-resistant carrying bag with a matching neck belt was supplied with the set. It allows the receiver to be carried on the chest under harsh conditions, such as rain.

The carrying bag is shown in the image on the right and has space for the receiver and the accessory box. The receiver can be operated from within the carrying bag.
  

 
Earphone
The MRP-4 has two indicators for providing feedback about the intercepted (radar) signal: optical, via the meter at the front panel, and acoustically, via the earphones.

The earphone is connected to the small rectangular socket at the bottom right of the front panel. Spare earphones and L/R earbuds are supplied with the set.
  
Earphone

 
Speaker   MR
For training purposes, the earphones can be replaced by a speaker, so that more people can hear the acoustic indicator. A small suitable speaker is supplied with the set and is normally stored inside the accessory box.

The speaker was not recommended for covert and surveillance operations, as it would give the position of the interceptor away.
  
Speaker

 
Battery   AZ
The radio is normally powered by an internal 8.4V / 450 mAh NiCd battery that is installed at the back of the unit. As the receiver consumes approx. 20 mA, a full battery should last for about 12 hours at normal temperatures. The battery voltage can be checked with the meter. Each battery also holds a pair of tweezers.

To allow uninterrupted operation, one or more spare NiCd batteries were supplied with the set. Alternatively, the MRP-4 can be powered by an external power pack (also supplied) or any other 9V DC source.
  
NiCd battery

 
Mains AC battery charger   SN
The internal battery is normally recharged with the AC battery charger shown on the right. It is supplied with the set and allows the NiCd battery to be charged from the 220V AC mains.

The meter can be installed to monitor the charging voltage. This is the same (removable) meter as is used on the receiver's front panel.
  
Mains battery charger with meter and battery installed

 
Mobile DC battery charger   PN
When using the MRP-4 in a mobile environment, it is also possible to recharge the batteries from a 12V DC car battery. A suitable mobile charger is supplied with the set. It can be connected to the cigarette lighter socket of the car.

The mobile charger has the same physical shape as the mains charger, as shown in the image on the right. Both chargers share the same meter. Note that the AC and DC chargers were some­times combined into a single unit (see below).
  
Mobile charger with NiCd battery installed

 
Universal AC/DC battery charger   UN
With some MRP-4 units, the two battery chargers shown above (AC and DC) were replaced by a single one, named 'UN', shown on the right.

It has two power cords: one for connection to the AC mains and one for connection to a 24V DC source, such as the battery of a truck. If the UN unit was present, the SN and PN chargers were omitted. The UN charger was stored in the wooden transit case in the space that was normally taken by the other two chargers.
  
Universal AC/DC PSU

 
Battery terminal block   PP
If the existing methods for recharging the batteries are not available, for example when the DC charger is broken, they can also be charged by means of an improvised method.

In order to get access to the recessed contacts of the batteries, a brown pertinax terminal block is supplied. It can be installed on top of the battery and makes the (+) and (-) contacts available on two regular terminals.
  
Battery terminal block

 
External power adapter   PS
When using the MRP-4 in combination with an alternative power source (anything else than the internal NiCd battery), the external power adapter has to be fitted. This adapter is installed instead of the normal NiCd battery and has two connections: a 5-pin DIN socket and a coaxial socket. The latter is used for connection of the portable power pack or any other 9V DC source.

The adapter is held in place with a black tripod screw. The image on the right shows the adapter aside the battery bay.
  
Power adapter removed

 
External power pack   BZ
If the MRP-4 has to be used continuously for an extended period of time (i.e. several days or even weeks), the external power pack should be used instead of the small internal NiCd batteries.

The power pack takes 6 large 1.5V D-type batteries and can be carried around the neck using a supplied strap. Alternatively, it can be attached to a belt.
  
Portable power pack (external battery)

 
Power lead   KBZ
A short power lead is supplied for connection of the external power pack to the receiver. It is a short piece of coaxial cable with two silver-plated coaxial plugs at the ends. When using the external power pack, the internal battery should be replaced by the external power adapter.

The cable is used to connect the external power pack to the coaxial socket on the adapter.
  
Power cable

 
External power cable   KVZ
A separate cable is supplied to allow the MRP-4 to be powered from another (external) DC power source. This can be useful if all other methods are unavailable, if the batteries are flat, or when the receiver is used in a fixed setup such as a static or mobile monitoring station.

It allows the MRP-4 to be powered by an alternative 9V DC power source, such as a battery or a mains power supply unit (PSU).
  
External power cable

 
Test unit   KG
The small cylincdrical unit shown in the image on the right was supplied with each MRP-4 to test its functions. The device contains a small electromagnetic relay that is powered by a single 1.5V D-type battery.

The device produces enough static noise from switching its contacts, that it can be heard on any of the four frequency bands. In practice it was used to check whether the detector diode for each band was still functioning properly.
  
Test unit (noise generator)

 
Spare meter
The meter is a special, versatile and fragile instrument. It is used as a signal indicator on the body of the receiver. The same meter is also used for checking the voltage when charging the batteries. As the same meter is used in three places, it has been constructed as a plug-in unit.

The meter can be pulled out of the receiver's front panel and can be installed in one of the chargers. As the meter is a fragile instrument, a spare one is supplied in the accessory kit. It is usually store inside a small plastic container.
  
Spare meter in box

 
Tweezers
When replacing a broken detector diode, there is a chance that after taking out the black fitting, the diode is left behind inside the socket. For this reason a pair of tweezers is supplied with every NiCd battery. In fact the tweezers are stored inside the side of the NiCd battery.

The tweezers are short and are shaped in such a way that a diode can be held without damaging it. Replacing a diode is further described below.
  
Tweezers

 
Spare diodes
At the heart of the MRP-4, a set of four detector diodes are used. As these devices are sensitive to static discharge and EMP, four spare D608A diodes were supplied with each kit.

The diodes were usually supplied in a plastic sealed bag as shown in the image on the right. Each diode is individually packed inside a lead cover to protect it against static discharge and EMP whilst in transit.

 More about the diodes
  
Spare detector diodes in plastic packaging

 
Maintenance logbook
In most cases, the MRP-4 came with some kind of logbook that holds the release date, parts list, issuing status and repair/maintenance record. The booklet shown on the right, was issued with an MRP-4 that was used in Poland. It reveals that the unit was manufactured in 1974 and that it was used until 2012.

We do not show the contents of this booklet as it contains names and signatures of actively serving Polish military personnel (2016).
  
Maintenance logbook

 
MRP-4 in wooden supply case Transit case Inside the transit case Inside the transport case MRP-4 with accessories inside carrying bag Carrying bag - bottom view Carrying strap
Speaker Earphone Earphone NiCd battery NiCd battery Mains battery charger Installing the meter Mains battery charger with meter and battery installed
Mobile charger with NiCd battery installed Universal AC/DC PSU Battery terminal block Battery terminal block - bottom view NiCd battery with terminal block NiCd battery with terminal block installed Power adapter removed Portable power pack (external battery)
Inside the portable power pack Power cable Power plug External power cable Test unit (noise generator) Test unit Plastic box with spare meter Spare meter in box



 
Interior
Despite its simple function, the MRP-4 is a complex device with many rigid Super High Frequency (SHF) parts mounted in a rather small space. The parts are housed inside a heavy die-cast metal enclosure and can be accessed from the rear side of the unit, by removing the rear panel.
 
This is done by removing 13 large bolts from the rear panel after which it can be taken off. Note that one recessed bolt may be sealed with a wax seal and that another one covers a test point. The image on the right shows the interior of the MRP-4 after the rear panel has been removed.   
MRP-4 interior

 
MRP-4 interior MRP-4 interior Top view
Block diagram
Although we do not have access to the technical description of the MRP-4, we can make a few educated guesses after studying the interior. The device has two antennas: a small one for the highest frequencies (bands I and II) and a larger one for the lower frequencies (band III and IV). Each band has it own D608A detector diode, as shown in the simplified block diagram below.


After selecting the desired band, the detected signal is amplified and sent to the earphones or speaker. The signal is also shown on the visual indicator (meter). Note that the actual band selector is more complex, as it also allows band I and II to be monitored simultaneously. The same is true for bands III and IV. The adjustable tone generator is not shown here.

 
Detector diodes
One of the most critical parts of the MRP-4 is the Russian detector diode D608A (Д608А). It is extremely sensitive to static discharge and spare ones were usually supplied with each kit. After 1994, even this Russian diode was given an NSN number: 5840-99-972-1922. It is still available today from Russian sellers on eBay. Note that the fitting for the Band IV diode has left-handed thread, which is why a spare Fitting IV was supplied. Turning it counter-clockwise tightens it!
 
  1. D608A
  2. D608A
  3. D608A
  4. D608A ← counter clockwise thread
When a broken diode has to be replaced, open its fitting by rotating its black cap counter clockwise (or clockwise if you are replacing the band IV diode). If all goes well, the diode will be clamped in between the silver-plated contacts of the cap, and will come out with the cap.
 
Sometimes however, the diode does not come out with the cap and stays behind in the socket. If this is the case, the special tweezers that came with the set have to be used to pull it out again.

The tweezers are usually stored inside a hidden bay at the side of each NiCd battery. They have been shaped in such a way that they can hold the diode without damaging it. Once the old diode is removed, a new one can be installed between the silver-plated contacts of the cap. Be certain not to bend the contacts when doing so. If one of the contacts is bended, repair it first.
  
Pulling the diode from the socket

Also, ensure that the open end of the diode (with the tiny little contact tip at the centre) is visible. Next, carefully re-install the cap and ensure that the diode goes in smoothly. If it binds, remove it and try again. Never use excessive force. With the diode all the way in, screw the cap in tightly.
 
A pack of four spare D608A diodes was supplied with each kit, commonly sealed in plastic. To protect the diodes against static discharge and strong EMP, 1 for example after a nuclear blast, each diode was individually covered in lead.

The image on the right shows a typical D608A diode as it was commonly supplied. The lead cover has been partly peeled off to reveal the diode inside. The diode can now be removed from its protective cover, but one has to be careful not to touch the contact tip at the other end. Always hold the diode at the closed end.
  
Partly unpacked diode

When replacing a diode, ensure that the closed end is fitted inside the cap and the contact tip is facing outwards, as shown here. When repairing a broken MRP-4 unit, spare D608A diodes can usually be found on auction sites such, as eBay as New Old Stock (NOS) items (2016).
 
  1. EMP = Electromagnetic Pulse. → Wikipedia

Releasing the diode fitting Pulling the diode from the socket Tweezers pulled out of the socket Diode clamped in the cap Screwing-in the diode tightly NiCd battery with tweezers stored in a hidden bay Taking the tweezers out of the storage bay Short pair of tweezers with rounded tips
Spare detector diodes in plastic packaging Spare detector diodes in plastic packaging Detector diode in lead cover Unpacking the diode from its protective lead cover Partly unpacked diode Unpacked diode Detector diode Detector diode
Checklist
Item Description Part number Qty
 
Combat setup   stored inside item 12
1 Radar seeker 7QP 740 01 1
2 NiCd battery AZ 7 NiCd 458 2
3 Tweezers (inside NiCd battery) 7QA 947 67 2
4 Earphones 7QK 643 85 2
5 Spare diode D608A 1 D 608 A 4
6 Test generator KG 7QK 050 92 1
7 Connection box PS 7QN 052 03 1
8 Terminal block PP 7QF 805 22 1
9 Meter (in container) 7QV 825 84 1
10 Universal power cable KVZ 7QK 644 04 1
11 Power cable 7QF 514 56 1
12 Carrying bag 7QV 791 01 1
13 Neck strap 7QF 817 84 1
14 Strap 7QF 817 75 1
 
Training accessories
15 Mains charger SN 1 7QN 290 03 1
16 Mobile charger PN 1 7QN 290 04 1
17 Portable power pack BZ 7QN 052 08 1
18 Cable for power pack KBZ 7QK 643 87 1
19 Speaker MR 7QN 617 01 1
20 Watchmaker screwdriver - 1
 
Documentation
21 Technical description - 1
22 Quick start guide - 1
23 Battery logbook - 1
24 Checklist (this list) - 1
25 Storage plan - 1
 
Spares
26 Spare NiCd battery AZ 7 NiCd 458 1
27 Tweezers 7QA 947 67 1
28 Holster 7QV 825 04 1
29 Miniature handset 7QK 643 85 1
30 Mounting bolt for diode I - III 7QF 847 53 1
31 Mounting bold for diode IV (lefthand threat) 7QF 847 54 1
32 Tripod screw 7QA 486 42 1
33 Earbuds (left) 7QA 423 21/23 1
34 Earbuds (right) 7QA 423 26/28 1
35 Storage case 7QV 165 06 1

 
  1. With some MRP-4 units, items 15 and 16 were replaced by a single universal charger, marked 'UN'.

Storage plan
The storage plan below shows where the various items are stored inside the transit case and the accessory box. This storage plan is usually present inside the top lid of the transit case.



 
Technical specifications
  • Receiver
    Direct conversion, with RF filters, video detectors and video amplifiers
  • Frequency
    1 - 10 GHz, 2.7 to 32 cm, divided over 4 user-selectable sub bands
  • Indication
    Optical (meter), acoustic (speaker or earphone)
  • Method
    Direct or Differential
  • Power
    8.4 V DC
  • Current
    20 mA
  • Uptime
    12 hours (with internal NiCd battery)
  • Size
    24.5 x 18.5 x 60 cm
  • Weight
    3700 g
Help required
We are still looking for the operating manual for the MRP-4 and/or any document that was originally supplied with the device. If you have any of these available, or if you know how to operate this unit, please contact us.
 
Documentation
  1. MRP-4 Maintenance booklet (Polish)
    S/N 0322 74. Issued 10 November 1974. #CM302378. 1

  2. MRP-4M Technical manual (Czech)
    R219 584N. 1995. 2

  1. This booklet is held in the collection of Crypto Museum, but is not available for download as it contains names and signatures of actively serving military personnel (2016).
  2. Manual kindly provided by ZKRAT (www.zkrat.com).

References
  1. Valka, CZK - MRP-4 (miniature radar locator)
    Website (Czech). Retrieved July 2016.

  2. Radiomuseum, Miniature Surveillance Radar Receiver MRP4-VS - IRLS-4
    Retrieved July 2016.

  3. Karsten Hansky, MRP-4 operations
    Personal correspondence, June 2016.

  4. Frank Davis, Czechoslovak armored recon
    10 April 2013.

  5. Valery C. Keaveny Jr., Ensuring the Continued Relevance of Long Range Surveillance Units
    2015. ISBN 978-178625344-6.

  6. DAF YP408, Image of ZB-298 doppler radar in use
    Website. Retrieved July 2016.

Further information

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Crypto Museum. Created: Tuesday 26 July 2016. Last changed: Friday, 10 February 2017 - 22:34 CET.
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