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Bodrog   TI-667
Bug receiver

Bodrog 1 was a device for the reception of miniature covert radio transmitters (bugs), operating in the VHF or UHF band. The device was developed in Czechoslovakia around 1972, by Správa 6 2 and was used by the Secret State Police (StB) and Správa 2 3 (counter-intelligence). It features manual tuning and has an automatic scanning facility. Bodrog was succeeded in 1976 by Dunaj.

Without the PSU, the receiver measures 200 x 180 x 65 mm and weights approx. 1 kg. All controls and connections are at the front panel, except for the mains power, for which a fixed cable is present at the rear. The AC mains PSU is removable. It can be swapped for a battery pack.

The receiver has a Variable Frequency Oscillator (VFO), operated with the large dial at the left. Tuning is controlled by varicaps, which makes it possible to use it as a scanner. Different versions were available, each with a specific frequency range. The device shown here is the A-variant.
Bodrog bug receiver

The covert radio bugs that were used with Bodrog, were low-power wide-band FM transmitters, operating on a quiet frequency that would normally not be noticed by the average listener. The A-version was used for receiving bugs that worked in the VHF-H band (153-165.5 MHz), whilst the B-version was used for UHF bugs (355-383 MHz). Optionally, the receiver could be fitted with a descrambler or a decoder, which was useful for scrambled bugs or subcarrier modulated bugs.

  1. Bodrog is a river in Slovakia.
  2. Správa 6 refers to Government Department 6 - Spojovacia Technika (communication technics).
  3. Správa 2 refers to Government Department 2 - Kontrarozviedka (counter-espionage).

Original packaging Inside the packaging Bodrog bug receiver Front panel Battery pack Mains PSU Rear view with PSU attached Antenna
Different versions of the Bodrog receiver were made, each with its own specific frequency range. The variant is indicated with a letter of the latin alphabet (e.g. 'A') and is printed in purple on the front panel, to the right of the tuning dial. The following versions are currently known:

The diagram below shows the location of the various controls and connections at the front panel of the Bodrog receiver. The antenna is connected to the BNC socket top right. When using the supplied rod antenna, the additonal 90° BNC adapter should be used. A small built-in speaker is located at the right side. An earpiece can be connected to the 3 mm socket 1 at the bottom right. When used, this disconnects the built-in speaker. A recorder can be connected to the 270° DIN socket at the bottom right. It provides the received audio, +12V power and a start/stop contact.

The mode of operation is controlled with the six black buttons at the bottom edge. The red button at the right, marked ZAP. (zapnuto), is the ON/OFF switch. The receiver can be tuned manually, using the dial at the left, or automatically (scanning) by pressing the AUT. button. Scanning stops as soon as a signal is found, and can be resumed by pressing the START button.

The meter normally gives an indication of the frequency, with a full meter reading corresponding to the upper edge of the frequency range. The meter can be converted into a field-strength indicator by pressing the SMĚR button. The battery voltage can be checked by pressing the BATT button momentarily. The squelch treshold is adjusted with the ŠUM knob at the top right and can be opened continuously by pressing the UMLČ button. On versions that have an optional decoder fitted, the DEKOD. button is used to turn it on and off 2 (otherwise the switch is unused).

  1. Note that the earphone socket requires a 3 mm jack plug (not 2.5 or 3.5 mm).
  2. It is currently unknowm whether the decoder was a descrambler or an extra demodulator. The latter was used with bugs of which the audio was modulated on a sub-carrier.

Front panel Tuning dials (fine and coarse) Meter with light-button 3 mm earphones socket 50 ohm BNC antenna socket and DIN connector for recorder

detachable mains 120/220V AC PSU battery pack for 10 AA-size cells 1/4 lambda rod antenna with BNC plug 90 BNC adapter for antenna Small mono earphones with 3 mm jack plug 6-pin 270 DIN plug for connection to recorder Operator and service manuals (wanted)
Mains PSU
Bodrog is usually powered by a mains power supply unit (PSU) that is attached to the rear side of the receiver by means of a large bolt at the center. It is suitable for connection to the 120V or 220V AC mains (selectable) that is used in most European countries.

The mains adapter has a fixed power lead with a universal 2-pin plug at the end, suitable for most European wall sockets.
Mains PSU

Battery pack
For mobile applications, the receiver can be powered by batteries. For this, the mains PSU is replaced by a battery pack that has roughly the same size. Like the PSU, the battery pack can be attached to the rear of the receiver.

It should be loaded with ten 1.5V AA-size cells. When using NiCd cells (1.2V each), this produces the required voltage of 12V DC.
Battery pack interior

For optimum reception, Bodrog should be used with an outdoor antenna, fitted on the roof of a building or car. If the receiver is used in close proximity of the transmitter however, the simple rod antenna that is supplied with the kit, can be connected directly to the BNC socket at the front, using the supplied 90° angle BNC adapter.

The antenna shown here is supplied with the VHF-version of the receiver (Bodrog-A) and is 26 cm long, shorter than the required 1/4 λ length of ± 44 cm.
Antenna with BNC adapter

Audio is normally delivered by the small built-in speaker at the right side of the receiver. When used in covert operations with a high chance of detection, a standard dynamic earpiece could be connected to the 3 mm jack socket at the front.

When the earpiece is used, the built-in speaker is switched OFF.

Recording cable
A recorder can be connected to the 6-pin 270° DIN socket at the bottom right of the frontpanel. The audio from the receiver is available on this connector at LINE level, plus an open collector output for starting the recorder as soon as a signal is detected and stopping it when the signal disappears again.

 Pinout of the socket

We are still looking for the operator's manual of this receiver and, if possible, also for any technical documentation. If you have any of these available, please contact us.   

Rear view with PSU attached PSU removed from the Bodrog receiver Spring-loaded power contacts on the receiver Mains PSU Battery pack Battery pack Opening the battery pack Battery pack interior
Earpiece Earpiece connected to the receiver Antenna 90dg BNC adapter Antenna Antenna with BNC adapter Standard antenna fitted to the Bodrog receiver Standard antenna fitted to the Bodrog receiver
Below is a description of the interior of the Bodrog receiver. Please note that the images shown below are of the Bodrog-A variant (i.e. the VHF version). The B-version (UHF) is quite similar, but has a different type of downconverter fitted at the right side of the device (the encapsulated area).

Bodrog A
The interior of the Bodrog receiver can be accessed by removing the PSU (or battery pack) and then the two screws from the rear panel. This allows the black cover to be removed towards the rear. The unit consists of an aluminium frame with components and PCBs at all sides, mounted to the front panel. Nearly all components in the receiver are manufactured by the TESLA factory.

The image on the right shows the receiver as seen from the rear right corner. At the far right are the spring-loaded contacts for connection of the battery or the PSU. The front panel is at the left with the speaker clearly visible at the side.

To the right of the speaker (mounted on its side) is the VHF-H down­converter, that is shown here with the metal shield removed. It contains the RF pre-amplifier, the VFO and the first mixer, all of which are varicap-controlled. The input of the downconverter is connected directly to the BNC socket at the front panel via a short coax cable.
Bodrog-A interior

The output of the downconverter is connected to the input of the receiver board that is mounted directly behind it. It contains a 48.5 MHz crystal oscillator and various mixers and amplifiers. The signal is then demodulated by a MAA661 amplifier/demodulator made by TESLA [2][3]. At the far side, with the green capacitors, is the AF filter, squelch control and the AF amplifier that delivers the signal to the built-in speaker. The small circuit in the middle is probably the recorder driver.

The bottom side of the frame holds another set of PCBs, of which the scanner board is always present. It controls the tuning voltage of the varicaps when scanning. The entire frequency band is scanned in approx. 2 seconds by applying a saw-tooth voltage to the varicaps Scanning is stopped as soon as a signal is detected. In the empty space aside the scanner board the optional decoder can be fitted. This was a factory-fit option and not a user-installable one.

Bodrog interior Interior seen from the rear Bottom side Downconverter Top side Scanner (bottom side) VHF-H downconverter (Bodrog-A) Front panel seen from the inside
Bodrog B
The B-variant of the Bodrog receiver is built on the same chassis and has the same controls and connections, but supports a different frequency range: 355 - 383 MHz (UHF). For this reason the Bodrog-B has a different downconverter inside the metal enclosure at the radio's right hand side.

The image on the right shows the downconverter of the Bodrog-B after the metal shield has been removed [1]. It is housed in a silver-plated milled brass case with 10 compartments. The antenna input is at the top left and the output is at the top (2nd compartment from the right).

In the enlargement of the image, the varicaps are clearly visible in the lower 4 compartments. They are used for the adjustment of the Variable Frequency Oscillator (VFO), the pre-amplifier, the mixer and the filters. The varicaps are driven directly by the scanner board at the bottom side.
Bodrog-B UHF downconverter. Photograph supplied by Miro Hornik [1].

Incidently, the Bodrog-B receiver shown in the above image, also has the optional decoder board fitted at the bottom side, next to the scanner board. This option is used for decoding scrambled bugs (or sub-carrier modulated bugs) and is controlled by the DEKOD. button at the front panel.

Bodrog-B UHF downconverter. Photograph supplied by Miro Hornik [1]. Bodrog-B with decoder board fitted. Photograph supplied by Miro Hornik [1].
Block diagram
The diagram below shows the simplified block diagram of the Bodrog receiver. At the top left is the downcoverter with built-in VFO that converts the VHF or UHF signal to 37.8 MHz. This signal is then fed into the actual receiver that mixed it with 48.5 from a crystal oscillator, producing a 10.7 MHz wideband FM signal which is demodulated and fed into the AF amplifier at the far right.

Note that not only the VFO, but all of the filters and the mixer of the downconverter are varicap controlled, which means that the filters are constantly tuned whilst tuning or scanning. This greatly improves the selectivity of the receiver. As an option, the receiver could be fitted with a descrambler that was connected between the demodulator and the AF amplifier. It was used for descrambling signals from a scrambled bug. If this decoder is fitted, the DEKOD. switch at the font panel is used to turn it ON and OFF. It is not fitted in the Bodrog-A receiver shown here.

  1. Not connected
  2. Record (?)
  3. 12V (switched)
  4. Unknown (7.13V)
  5. Line out
  6. Ground
  • Frequency
    A (VHF: 153-165.5 MHz), B (UHF: 355-383 MHz)
  • IF1
    37.8 MHz
  • IF2
    10.7 MHz
  1. Miro Horník, OM3CU, Personal correspondence
    August 2015.

  2. Tesla, MAA-661 datasheet
    Date unknown. Retrieved September 2015.

  3. Tesla, Analogue ICs
    1987. Retrieved September 2015.
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Crypto Museum. Created: Thursday 20 August 2015. Last changed: Wednesday, 12 April 2017 - 09:50 CET.
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