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Path loss survey system

URS-4 is a complete test system for investigating the path attenuation or path loss in a specific VHF/UHF covert radio system, developed in 1978 by the Dutch radar Laboratory (NRP) for the US Central Intelligence Agency (CIA). It was used for analysing the link budget 1 of a communications system, consisting of two covert listening devices (bugs), a surveillance receiver and antennas.

The URS-4 was intended as the successor to the URS-1 that had been developed back in 1971. It supports the same 316 MHz UHF band as the URS-1, but adds support for the 170 MHz VHF-H band, through an exchangable plug- in unit.

Furthermore, it offers the same user interface as the URS-3 and allows the same accessories to be connected and used in the same manner. This applies in particular to the ability to record a complete survey onto (audio) tape and play it back at the office later. It also offers support for the connection of a pen recorder (data printer).
URS-4 path loss survey set

A complete URS-4 consists of an URR-4 receiver with VHF and UHF plug-ins, a portable URT-4L transmitter for the low frequencies (170 MHz), a portable URT-4H transmitter for the high band (416 MHz), suitable VHF and UHF antennas and a wide range of accessories. Note that the URS-4 is a narrow band system (30 kHz) whereas the 1500 MHz URS-3 is a wide band system (25 MHz).

Development of the URS-4 started in 1978, shortly after introduction of the URS-3. After several tests and improvements, it went into production in 1980. In 1982, some modifications were made to the front panel of the URT-L transmitter. The URS-4 was in production until at least 1991.

  1. In a telecommunications system, the link budget is the sum of all gains and losses from transmitter, through the medium to the receiver.  Wikipedia

URS-4 path loss survey set URS-4 path loss survey set URT-4L with antenna and remote MARK button connected
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URS-4 path loss survey set
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URS-4 path loss survey set
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URT-4L with antenna and remote MARK button connected

The diagram below shows the basic setup of the URS-4 system. At the left are the 2 transmitters of which the URT-4L is used for the low band (170 MHz) and the URT-4H covers the high band (416 MHz). The URT-4H is powered by a single 9V block battery, whilst the URT-4L needs four AA-size batteries for a total of 6V. When ON, the transmitter produces a constant beep that should be picked up by the receiver. An optional external push-button can be connected to a socket, to allow the transmitter to send a 1350 Hz MARK tone, allowing easy identification at the listening post (LP). Each transmitter needs it own (frequency-specific) Sleevex antenna.

At the right is the URR-4 receiver that should be connected to two and SRN-55 antenna for the UHF band and a separate open dipole antenna for the VHF band. The receiver produces a visible output on an indicator at its front panel. Furthermore, sockets are available for the connection of a pen recorder and an audio tape recorder, for later reference and processing the head office.

The illustration below shows some of the factors that attribute to path loss, starting with the type and position of the bug and its antenna at the target area. The transmitter's signal is attenuated by the distance to the receiver, the material in which the antenna is embedded, the walls of the building, any furniture, and by anything else that is in the signal path to the Listening Post (LP).

Possible causes of path loss

Other factors may attribute to the gain of the signal, such as the transmitter's output power, the gain (if any) of its antenna, the gain of the receiving antenna and any pre-amplifiers. In order to predict the propagation of the signal with some degree of reliability, it may be useful to calculate the sum of all gains and losses and compare it to the link budget of the entire system. A detailed path loss survey was usually carried out by the CIA before planting a bug at a given target.

Modified Samsonite briefcase Universal radio transmitter URT-4L (low-band) Universal radio transmitter URT-4H (high-band) Universal radio receiver URR-4 Low-band converter Data recorder/writer Remote control push-button Listening Post (LP) antenna for receiver
Dipole antenna for VHF (169 MHz)
Listening Post (LP) antenna for receiver
Samsonite briefcases
All parts and accessories of the URS-4 survey system were supplied in two standard Samsonite executive style briefcases, such as the one shown in the image on the right. Documentation and antennas were stowed in the top lid.

All other parts are stowed in the bottom part, that consist of two layers. The transmitter and the receiver are directly accessible. Adapters and cables are stored in the bottom section.
Samsonite briefcase with URS-1

VHF transmitter   URT-4L
The image on the right shows an original URT-4L transmitter, without batteries and without enclosure. The one shown here, is fully operational and transmits on 169 MHz.

The transmitter is powered by a 4.5V battery, consisting of three 1.5V AA-size cells, fitted in a battery holder that is connected to the clips at the bottom of the transmitter.

 More information
URT-4L transmitter

UHF transmitter   URT-4H
A similar but smaller transmitter was supplied for support of the UHF frequencies in the 316 MHz band. THis transmitter is somewhat smaller than the URT-4L and is powered by a standard 9V block battery.

Unfortunately, we do not have an URT-9H transmitter in our collection, so we are unable to show a picture of it at this time.

No image available

Receiver   URR-4
The URR-4 shows great resemblance to the URR-3 receiver. As we do not have an URR-4 in our collection, we are showing an image of the URR-3 instead.

The front panel of the URR-4 is wider than that of the URR-3 in order to accomodate the VHF and UHF plug-ins, which is accessible from the front panel.
No image of the URR-4 is currently available, so we are showing an image of the very similar URR-3 instead

Low-band converters
The URR-3 receiver was supplied with two plug-in units, one of which was installed into a bay at the left side of the front panel. One plug-in was for the VHF band (169 MHz), whilst the other one was for the UHF band (316 MHz).

The image on the right shows the VHF variant. It has a BNC socket for connection of the VHF dipole antenna, and a rotary switch to select the desired frequency: 168, 169 or 170 MHz.
Low-band converter for URS-4

Data recorder   RE-510
When performing a site survey, the results of the path loss measurements can be printed onto paper, using the Goertz RE-501 MINOGOR pen recorder shown in the image on the right.

The device is battery powered and prints the data, relative to time, onto a 20 cm wide thermal paper strip for later processing.
Goertz Minigor RE-501 data recorder

Tape recorder   UHER
In addition to printing the measurement data onto paper, it was also possible to record it onto a magnetic (audio) tape, using the UHER recorder shown in the image on the right.

UHER tape recorders were very popular during the 1960s and 1970s, as they were among the first affordable portable tape recorders with professional performance.

 More information

UHER 4000 Report-S

Remote switch
When transmitting, the URT-4L and URT-4H transmitters produce a 1250 Hz tone. This can be used a the receiving end to tune-in on the signal. Both transmitters have an SMB socket to which a wired push-button can be connected.

Whilst pressing the button, the transmitted tone changes to 1350 Hz, so that the transmitter can easily be identified at the receiving end.
Remote switch

Receiver VHF antenna
For the VHF frequencies around 169 MHz, this standard reference antenna was used. It is an open dipole of which the impedance has been matched to the 50Ω output of the transmitter.

The dipole is attached to the end of a horizontal boom at the end of which is the feed point. It is connected to the receiver via a 5 metre long BNC-BNC cable.
Open dipole antenna for VHF 169 MHz

Receiver UHF antenna   SRN-9M
For the UHF frequencies around 316 MHz, the SRN-9 was supplied. It is basically a center-fed half-wave (½λ) open dipole that is placed before a reflective shield. The total gain of this antenna is estimated at 8.5dB.

Inside the boom (between the two dipole elements and the reflector) is a BALUN that provides correct matching to the coaxial transmission line.

 More information

Directional LP antenna

Sleevex antennas
The URS-4 set was supplied with two complete sets of Sleevex antennas (three models each), so allow testing with two the independent transmitters (URT-4L and URT-4H) on VHF and UHF, in combination with the URR-4 receiver.

Each Sleevex antenna has a colour coded ring at its base, that indicates the environment (medium or diëlectricum) for which it has been designed.

 More information

Yellow Sleevex antenna

Equipment list
  • Receiver URR-4
  • Plug-in unit for 168 - 169 - 170 MHz
  • Plug-in unit for 314.5 - 315.5 - 316.5 MHz
  • Transmitter URT-4L (168, 169 or 170 MHz)
  • Transmitter URT-4H (314.5, 315.5 or 316.5 MHz)
  • Dipole antenna for 169 MHz
  • SRN-55 antenna for 316 MHz
  • Sleevex antenna for 169 MHz
  • Sleevex antenna for 315.5 MHz
  • Attenuator 80 dB
  • Extender board for internal plug-in cards of URR-4
  • Battery input voltage extender
  • Tape in/out test cable
  • BNC-BNC coax cable 5 m
  • DIN-DIN audio cable 1 m
  • BNC-Banana cable (1 m) for pen recorder
  • Remote button (marker) for URT-4L and URT-4H
  • Carrying strap for URR-4
  • Spare DIN plug
  • 5 spare fuses 100 mA
  • Allan wrench
  • Screwdriver
  • Operation and test manual
  • Set of final acceptance test data sheets
Technical specifications
Complete system   URS-4
  • VHF measuring range
    70 dB to min. 160 dB ± 3 dB
  • UHF measuring range
    50 dB to min. 140 dB ± 3 dB
  • Marking range
    VHF: min. 160 dB, UHF: min. 140 dB
Receiver   URR-4
  • VHF frequencies
    168, 169 and 170 MHz ± 2 kHz
  • UHF frequencies
    314.5, 315.5, and 316.5 MHz ± 3 kHz
  • Gain accuracy
    ≤ 0.5 dB
  • Image suppression
    VHF ≥ 45 dB, UHF ≥ 40 dB
  • IF suppression
    ≥ 70 dB
  • Input impedance
    50 Ω
  • Noise figure
    < 4 dB
  • RF - IF bandwidth
    12 kHz ± 2 kHz
  • Modulation (tone)
    1250 Hz ± 10 Hz
  • Mark tone
    1350 Hz ± 10 Hz
  • Midscale (meter)
    -99 dB ± 1.5 dB
  • Indicator accuracy
    20-100% of full scale: ± 2dB, 10% of full scale: ± 4dB
  • Pen recorder out
    > +500 mV (FSD)
  • Tape recorder out
    > 350 mV RMS
  • Tape input
    < 350 mV RMS
  • Frequency out
    ZERO: 500 Hz ± 15 Hz, FSD: 3000 Hz ± 25 Hz
  • Voltage
    +14 to +20 V, minimum: +13.5 V
  • Current
    REC: < 30 mA, REPLAY: < 12 mA
  • Battery
    4 x 9V block battery
  • Dimensions
    290 x 200 x 89 mm
  • Weight (incl. batt.)
  • Temperatureq
    -18°C to +50°C
VHF Transmitter   URT-4L
  • Frequency
    168 or 169 or 170 MHz ± 2 kHz
  • Output power
    +22 dBm (160 mW) ± 1 dB
  • Impedance
    50 Ω
  • Harmonic suppression
    > 30 dB
  • Tone frequency
    1250 Hz ± 10 Hz
  • Mark frequency
    1350 Hz ± 10 Hz
  • Modulation
    on-off keying
  • RF bandsiwdth
    ≤ 30 kHz
  • Supply voltage
    4.5 to 7 V (minimum 4.5 V)
  • Current
    < 320 mA
  • Battery
    4 x AA-size penlight (1.5V each)
  • Dimensions
    61 x 21.5 x 171 mm
  • Weight
    ~ 320 grams (without batteries)
  • Temperature
    -18°C to +50°C
  • Antenna type
  • Antenna socket
  • Mark socket
    Sub-Minax/F (SMB)
UHF Transmitter   URT-4H
  • Frequency
    314.5 or 315.5 or 316.5 MHz ± 3 kHz
  • Output power
    +2 dBm (1.6 mW) ± 1 dB
  • Impedance
    50 Ω
  • Harmonic suppression
    > 30 dB
  • Tone frequency
    1250 Hz ± 10 Hz
  • Mark frequency
    1350 Hz ± 10 Hz
  • Modulation
    on-off keying
  • RF bandsiwdth
    ≤ 30 kHz
  • Supply voltage
    6.5 to 10 V (minimum 6.5 V)
  • Current
    < 10 mA
  • Battery
    9 V block battery
  • Dimensions
    28 x 20 x 165 mm
  • Weight
    ~ 150 grams (without batteries)
  • Temperature
    -18°C to +50°C
  • Antenna type
  • Antenna socket
  • Mark socket
    Sub-Minax/F (SMB)
  1. Tentative Proposal for Prototype XURS-4 Equipment
    NRP, 8 March 1978. CM302554/x.

  2. Technical Attachment to Proposal for Prototype XURS-4 Equipment
    NRP, 8 June 1978. CM302554/x.

  3. Proposal for Prototype XURS-4 Equipment
    NRP, June 1978. CM302554/x.

  4. Operating Manual for URS-4 Path Loss Measuring System
    NRP, June 1980. CM302554/x.

  5. Environmental Test Report on XURR-4 Receiver
    NRP, August 1980. CM302554/x.

  6. Environmental Test Report on XURT-4L and XURT-4H Transmitters
    NRP, August 1980. CM302554/x.

  7. Engeneering Considerations Related to XURS-4 Protype Equipment
    NRP, September 1980. CM302554/x.

  8. URT-4L Component Layout (technical drawing)
    NRP, November 1982. CM302554/x.

  9. Operating Manual for URS-4 Path Loss Measuring System
    NRP, January 1983. CM302554/x.

  10. Collection of correspondence between NRP and CIA about URR-4
    NRP/CIA, 21 January 1983. CM302554/x.

  11. Environmental Test Report on URS-4 Path Loss Measuring System
    March 1983. CM302554/x.

  12. Environmental Test Report on URS-4 Path Loss Measuring System
    May 1991. CM302554/x.

  13. XY-YT Miniaturschreiber Minigor, Type RE 501, Bedienungsanleitung
    Goetz, Metrawatt AG, Nürnberg (Germany). Date unknown. CM302559/A.
  1. NRP/CIA, Collection of documents related to URS-4
    Crypto Museum Archive, CM302554 (see above).
Further information
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Crypto Museum. Created: Thursday 10 August 2017. Last changed: Sunday, 13 August 2017 - 14:49 CET.
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