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Nagra PS-1
JBR playback system

The PS-1 was a high-end audio tape-based playback system for the Junior Body Recorder (JBR), introduced by Nagra Kudelski in Cheseaux-sur-Lausanne (Switzerland) in 1986, two years after the introduction of the body wearable JBR miniature recorder itself. The device uses a proprietary tape cassette format and was available only to law enforcement and intelligence agencies.
The Nagra JBR was a covert audio recorder that was initially developed for the FBI and two other US Government agencies, but was later also used by law enforcement in Canada and in the UK.

The JBR was introduced in 1984 and became an instant success, but as it was a recording-only device, a separate playback system was needed. The system had to be able to accept Nagra's propietary tape cassette format and, more importantly, it had to correct small variations in speed that were caused by the fact that the JBR does not have a flywheel/capstan mechanism.
Nagra PS-1 playback system for JBR covert recorder

Two years after the introduction of the JBR, during which time specially adapted Nagra SN units were used as a gap-fill solution, the PS-1 playback system was ready. It had a built-in Time Base Corrector (TBC) with an adjustable analogue delay line that used the 5.461 kHz signal on the JBR's control track to eliminated the short-term speed variations, also known as wow and flutter. The result is an accurate, sophisticated, capstan-less, and hence maintenance free, playback system with a high audio playback quality, built to the well-known Swiss manufacturing standards.

The PS-1 was introduced in 1986 and stayed in production for several years, along with the JBR miniature recorder. In total 657 PS-1 units were built (compared to 1118 JBR units) [2] for a unit price of CHF 16,000 (Swiss Francs, approx. 25,600 US$ in 1986). They were available only to law enforcement and intelligencies agencies in the US, Canada and the UK, and were never listed in the Nagra catalogue. For a long time they remained unknown to the public, mainly because the intelligence agencies forced Nagra to keep their existence secret for many years. The JBR and the PS-1 were the last electromechnical devices from Nagra before digital recording took over.
Nagra PS-1 with perspex dust cover Nagra PS-1 with dust cover open Nagra PS-1 playback system Nagra PS-1 playback system for JBR covert recorder Top view of the Nagra PS-1 Rear panel of the Nagra PS-1 Bottom view with battery compartment A Nagra JBR recorder in front of the Nagra PS-1

Complete system
A Nagra JBR recorder in front of the Nagra PS-1

Most of the controls of the Nagra PS-1 are at the top surface, which consists of an eloxed aluminium panel, with a solid spring-suspended sub-frame at the center. The sub-frame is milled out of a solid aluminium block and contains all mechanical (i.e. moving) parts, such as the motor, the tape guides and the tape tension arm. Furthermore it carries the playback head.

The rest of the top panel contains the usual controls, such as volume, balance (between the two channels) and equalizer. At the bottom centre are four grey buttons that are used to control the tape (LOAD, STOP, START and SPOOL). Furthermore, at the left centre is the expander adjustment that compensates for the fact that the JBR compresses the dynamic range during the recording.

Top view of the Nagra PS-1

The image above shows a close-up of the sub-frame that holds all mechanical parts. The large tape roller at the bottom left acts as a tape guide but also has a built-in optical encoder that is used to measure the current tape speed. It is used by the motor management system to guarantee a constant tape speed during playback. This is necessary because the PS-1 does not have a capstan with flywheel and has the advantage that the PS-1 is nearly mantenance-free. On top of that, the built-in Time Base Corrector (TBC) uses the 5.461 kHz signal from the recorded control track to correct any short-term speed variations, also known as wow and flutter.
At the bottom right is a panel with push-buttons that is normally covered by a spring-loaded panel. After lifting the flap, the buttons become visible. The buttons can be used to set or reset the tape length counter, or to jump to a certain section on the tape. After selecting the required function, the numbered keys are used to enter a value. The tape counter is pretty accurate.

The PS-1 can be powered by various sources. For desktop use, it is best powered from the AC mains. A recessed switch at the rear panel allows selection of the appropriate mains voltage.
Special functions

When used in the field, the PS-1 can be powered by the internal batteries (accessible via a panel in the bottom of the case), or an external DC source between 11 and 20V. The knob at the top left of the control panel is used to select the desired source, or disconnect the unit completely.

Most of the connections of the PS-1 are located at the rear panel, that also holds the mains power switch and the fuses. There are sockets for connection to the mains, an external 11-20V DC power source, line in and outputs, a footwitch, a remote control unit and an external TBC. The two side panels each hold one of the speakers, whilst the right side panel also holds the socket for connection of the headphones, plus a small slide switch to disable the speakers.
Top view of the Nagra PS-1 Top view of the Nagra PS-1 Rear panel of the Nagra PS-1 Right side Controls Special functions Tape roller with built-in speed meter Playback head

JBR covert recorder
As the PS-1 is a playback-only device, the tapes have to be recorded on a separate recording device. This is the Junior Body Recorder (JBR) that was release two years before the PS-1, in 1984. It was designed to meet the tough specifications of the FBI and was the smallest professional body-wearable recorder at the time.

Like with the PS-1, the existence of the JBR was kept secret for many years, in order to give law enforcement and intelligence agencies an advantage over criminals.

 More information
Nagra JBR with cover

Tape loading
For the Nagra JBR and the PS-1, Nagra developed its own proprietary tape cassette format that is not used by anyone else. The specifications of the tape itself are identical to that of the Nagra SN, but the supply and pickup reels are integrated into a single unit which is open at all sides.
At the beginning and the end of the cassette is a transparent piece of lead-in/lead-out tape that is used by an optical sensor on the sub-frame to sense the tape-end and stop the mechanism.

At one of the short sides of te cassette, the tape is exposed and can be touched. When loading the tape into the PS-1, this is where the tape has to be pulled-out carefully with a smooth non-metal tool. Pull it out just enough to guide it over the tension arm, the large roller and the playback head, as indicated by the arrows on the sub-frame and shown in the image on the right.
Loading and unloading the tape

Once the tape is loaded, the cassette holder can be closed by pushing it down into the lock at the front, after which the PS-1 will wind the tape back until the appropriate tension is sensed. The PS-1 is now ready for use. Whenever the cassette holder is opened, or when the tape breaks during normal use, the PS-1 will automatically enter LOAD mode again and release the tape.

The separate JBR records its audio onto a 3.81 mm chromium dioxide tape with three channels: two independent 1.2 mm audio channels plus a 0.4 mm control track at the centre. The latter is used for a 5,461 Hz reference signal that allows the PS-1 playback system to correct for speed variations later. The tape runs at a constant speed of 2.38 cm/s (15/16 ips) ± 2%. Depending on the thickness of the tape, the recording time is 90 minutes (12µ) or even 2 hours (9).
Nagra JBR tape cassette with tape-lock installed Open end of the tape cassette The sub-frame without a tape installed Loading and unloading the tape PS-1 with tape loaded and cassette holder open Opening or closing the cassette holder Unlocking the cassette holder Playback head with the tape running past it

Hidden features
Some functions and features, that are not normally needed by the average user, are hidden in the software. They can be accessed by pressing the red NUM key on the key pad at the bottom right (normally covered by a flap), followed by a three digit code. The following codes are available in versions 1.0 and 1.1 of the firmware:
  • 000
    Neutral code, no effect
  • 001
    Inhibit automatic low batt power off
  • 002
    Bypas the Time Base Corrector (TBC off)
  • 003
    Enable the built-in Time Base Corrector (TBC on)
  • 004
    Normal automatic Time Base Corrector switching
  • 005
    Bypass the audio expander
  • 006
    Normal automatic audio expander switching
  • 007
    Use tape roller speed stabilizer only (also bypasses the TBC)
  • 008
    Use control track speed stabilizer only
  • 009
    Automatic switching between tape roller and control track stabilizer
  • 010
    Set duration of 'backspace' footswitch 1
  • 011
    Inhibit fast spooling speed

  • 100
    Cancel all settings, except for command 010 2
  • 201
    Display the software version number momentarily
In addition, the following error codes may appear on the display:
  • 01
    Non existing numeric code requested
  • 02
    Illegal time setting attempt (e.g. 64 seconds)
  • 03
    Requensted tape position not found
  1. The default backspace setting is 2 sec. It can be set between 0 and 9 sec. This setting is retained when command 100 is executed (reset all).
  2. Note that command 100 is automatically executed each time the PS-1 enters LOAD mode (e.g. when pressing LOAD or when removing a tape).

In the mid-1980s, the FBI had a growing need for a sub-miniature undetectable tape recorder for critical surveillance tasks and wiretapping. As no portable tape recorder at the time met the tough specifications of the FBI - not even the Nagra SN - the FBI teamed up with Nagra Magnetics Inc., the US subsidary of the Swiss Nagra Company, to see if a proprietary unit could be developed [1].

It was decided that a new tape recorder would be designed, which would be smaller that any existing professional surveillance recorder and that would be virtually undetectable. On behalf of the FBI, Jim B. Reames helped the design team. It has been rumoured that his initials (JBR) were used as the name for the device, but this has neither been confirmed nor ignored by NAGRA [1].

In order to keep the new device as small as possible, it was decided to leave the play-back facilities out. Furthermore, the JBR had no erease head and used an uncommon frequency (32 kHz) for the recording bias signal. This frequency is also used by digital watches and would not be noticed by the recorder detectors that were commonly used at the time. As the JBR is housed in a solid aluminium enclosure, the remaining unwanted emission is kept to a minimum. For playback, the separate PS-1 device was developed, which became available a few years later.

As the US Government did not want the JBR to become available to other users, or even publicly known, it was decided to keep the device secret. It was not mentioned in any brochure and it was never shown and demonstrated at technology shows. All marketing for the unit had to be done via word of mouth. In September 1990, Nagra wanted to advertise the JBR in the Law and Order magazine, but received a letter from an undisclosed US Government agency that prevented them from doing so. If they did, the letter stated, NAGRA would lose all US Government contracts [1].

Besides the FBI, there were two other US Government agencies who had access to the newly developed JBR technology (one of which was probably the CIA). Later, other US Government Agencies were allowed to use the JBR too, and even some Canadian and British agencies were given access to the new technology.
Like all other Nagra products, the PS-1 is built to the highest possible manufacturing standards, both mechanically and electronically, and is very service-friendly. The interior can be accessed by removing four screws, two at the front and two at the rear, after which the top panel comes off.
Once the top panel has been removed, the first set of PCBs becomes visible. At the left are the control switches for the equalizer and the expander. At the front are the tape controls and the power switch, with an LDR that automatically dims the light when the unit is used in the dark. The lights can also be switched off completely.

At the right is the central processing unit, built around an NSC800 (Z-80) micro­processor that is hidden under the display. The CPU consists of the processor, an I/O expander, 2KB of RAM and an EPROM with the firmware; in this case 1.1.
Nagra PS-1 with top panel removed

At the center is the spring-suspended sub-frame with the mechanical parts. So far, all the parts and circuits are mounted to a horizontal frame that is bolted to the case. After removing four more screws, two at the top front and two at the top rear, the hinged frame can be raised.
The rear side of the hinged frame holds the motors and the break at the centre, and the driver circuits at the top right. At the centre left is the optical encoder that is used for accurately measuring the tape speed. The special tape-tension sensor is located just below the motors.

The bottom part of the PS-1 holds the Power Supply Unit (PSU) and the remaining electronic circuits. The PSU is located at the rear left and is built around a well-shielded toroid transformer. The rest of the PSU is hidden below the large motherboard that holds the remaining circuits.

The motherboard takes up most of the bottom section and holds no less than 12 sub-boards, each of which contains a particular circuit. Each sub-board is implemented as a plug-in card that can be swapped within seconds. There are separate audio amplifiers, equalizers and expanders for each channel plus boards for the optical encoder and the control track driven servo system.

One of the most important circuits is the Time Base Corrector (TBC) which is built around two RD5106ANP analogue delay lines [5] each of which provides an adjustable audio delay between 512µs and 1s. This is sufficient for cancelling out even the smallest speed variations in the recorded signal, within a certain window. Three such TBCs are available: one for each audio channel and one for the control track. The latter is the master TBC that controls the other two.
Nagra PS-1 with its top panel removed Nagra PS-1 with top panel removed NSC800 (Z80) microprocessor with peripherals Display unit Equalizer and expander controls Power switch and tape controls The Light Dependent Resistor (LDR) that dims the lights Close-up of the meter section
PS-1 interior after lifting the frame Rear side of the top frame holding the engines Close-up of the optical encoder and the motors Motor drivers Another view of the motors Close-up of the optical encoder Tape-tension sensor
Bottom section of the PS-1, with power supply unit, mother board and many electronic modules The PSU in the rear left corner of the case Extra PSU board mounter below the motherboard Two identical Time Base Correctors; one for each channel Meter circuit and peak indicator One of the audio equalizers Audio expander

Time Base Corrector
Any analogue audio recording contains small timing errors that are caused by variations in rotational speed of the mechanism. These variations will result in a frequency-modulated (FM) component in the recorded signal. Errors of this type are commonly known as wow and flutter [6] and consist of two components: slow 0.1-10 Hz variations (wow) and fast ones >10 Hz (flutter).

Normally, it is good practice to reduce the wow and flutter as much as possible in the recording device, e.g. by adding a flywheel to a tape recorder. In the Nagra JBR recorder however, the flywheel is omitted in order to reduce the size and weight of the device. Instead is has an advanced tape speed measuring system that controls the speed of the motor. This guarantees a more or less constant tape speed, but cannot compensate any short-term variations in speed.

To solve this problem, a 5.461 kHz reference signal is recorded onto a third track on the tape. This track is located in between the two audio tracks at the centre of the tape and is called the control track. During playback (i.e. in the PS-1), the signal from the control track is used to calculate any timing errors in the recorded signal. By temporarily storing a number of audio samples in a piece of memory (buffer) at varying speed, and reading them out at a constant speed, most short-term errors will be corrected. This process is called: Time Base Correction.

Simplified block diagram of the Time Base Corrector (TBC)

A Time Base Corrector (TBC) can only compensate for errors within a certain time frame or window, which is limited by the size of its buffer. Reaching the end of the buffer will cause a buffer overrun and result in a TBC error. To avoid this, the calculated error is also used to increase or decrease the overall tape speed by adjusting the motor management system accordingly (servo). The latter is a correction for any long-term speed variations.

A TBC can be implemented in two ways: in the analogue domain and in the digital domain. At the time the PS-1 was developed (1985), digital solutions were available but were costly in terms of money, size, weight and chip count. This problem was solved by using a so called bucket brigade device (BBD) [7], which is actually a clock-controlled variable analogue delay line in a single chip. Inside the PS-1, an RD5106A BBD-chip [5] from the US manufacturer Reticon was used. It offers a variable delay between 512µs and 1s and accepts clock signals between 500 Hz and 1 MHz.

In case the errors on the tape are too large, or if the control track has been damaged, the cure might be worse than the disease. In such cases the error lights on the control panel will be lit and it is advised to bypass the TBC. Furthermore, it is possible to use a proprietary external TBC that can be connected at the rear. Please note that, if an external TBC is used, the two red switches and the center of the motherboard should both be set to EXT (or back to INT for the internal TBC).
  1. Nagra Kudelski, PS-1 playback system
    Product brochure, 2 pages. June 1092.

  2. Nagra Kudelski, PS-1 Instruction manual
    Nagra PS-1 playback system for Nagra JBR cassettes. October 1987.

  1. Full Disclosure, The War on Privacy Hits You in the Pocket Book
    Full Disclosure Newspaper, Libertyville, Illinois (USA). 1991 Retrieved July 2014.

  2. Nagra, Production overview and quantities
    Internal Nagra document. Date unknown, but probably 2000.

  3. Nagra Kudelski, PS-1 playback system
    Product brochure, 2 pages. June 1092.

  4. Nagra Kudelski, PS-1 Instruction manual
    Nagra PS-1 playback system for Nagra JBR cassettes. October 1987.

  5. AG&G Reticon, RD5106A/RD5107A Analog Delay Line
    September 1991. Retrieved July 2014.

  6. Wikipedia, Wow and flutter measurement
    Retrieved July 2014.

  7. Wikipedia, Bucket-brigade device
    Retrieved July 2014.

Further information

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Crypto Museum. Created: Thursday 10 July 2014. Last changed: Monday, 16 January 2017 - 21:48 CET.
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