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Manpack short-wave transceiver - this page is a stub

The RUP-12 radio was a family of low-band VHF transceivers (30-70 MHz), developed in the former Yugoslavia in the late 1960s [1] and built by the Rudi Čajavec factory in Banja Luka (Bosnia and Herzegovina). It was intended for communication between infantry companies and battalions of the Yugoslav National Army (JNA). The RUP-12 is also known as UGAR-1. In the late 1970s, the RUP-12 was succeeded by the RU-2, which had identical controls but a modernised interior.

Voice scrambler
The RUP-12 is not suitable for a real voice encryption unit like the KzU-63 that was used with the later RU-2/2K.

In order to provide at least some level of voice protection on the RUP-12, a voice scrambler was sometime used, such as the Yugoslav KzU-61 or the American KY-189 that is shown in the image on the right. For the latter, the RUP-12 had to be modified (+12V on pin 5 of the connector).

 More information
KY-189 scrambler handset

Scale conversion
The RUP-12 is suitable for all low-band VHF frequencies between 30 and 70 MHz, with a channel spacing of 50 kHz, resulting in 800 discrete channels. The desired frequency is selected by means of 3 rotary switches at the front panel, between 000 and 799. For conversion between the channel number and the actual frequency, the following formulas can be used:

As an example, a scale setting of 367, results in (367+600)/20 = 48.35 MHz. The lowest setting (000), results in 30 MHz, whilst the highest setting (799) gives 69.95 MHz. Use formula (2) to calculate backwards. A frequency of 52 MHz, results in a scale setting of 20 · (52-30) = 440.

Block diagram
The image below shows a simplified block diagram of the RUP-12, and is based on several more detailed block diagrams from the operator's manual [2]. The transceiver parts (TX) are at the top, whilst the lower parts shows the various stages of the receiver. The audio frequency stages (AF) are at the bottom right. The receiver is a straightforward heterodyne with a 1st IF frequency of 10.7 MHz. Some parts of the receiver's 10.7 MHz section are shared with the transmitter (AFC).

The transmitter section is shown at the top (in red). The modulator at the right mixes the audio signal from the microphone with a 10.7 MHz signal from a crystal oscillator. The advantage of using 10.7 MHz is that the crystal reference of the receiver can be used for selecting the desired transmission frequency. The most complex part of the transceiver is the crystal reference itself:

The block diagram above shows how the crystal reference is synthesized. The analogue parts are shown in blue, whilst the (digital) logic parts are red. The three parts that determine the actual frequency are shown in blue. The leftmost one is based on a 5 MHz crystal oscillator with a configurable multiplier behind it. It allows the 5 MHz signal to be multiplied by 1, 2, 3 or 4. This signal is fed to the first mixer, where it produces a sum and a difference signal. If we also take 0 MHz into account (i.e. multiply by 0, i.e. no signal), the following 8 steps are possible:

-20, -15, -10, -5, 0, 5, 10, 15 MHz

These steps are controlled by the leftmost frequency selector on the front panel of the transceiver (0-7). The other two digits are determined by two crystal banks with 10 crystals each (0-9). The first one is added in the second mixer, whilst the third one is fed into a phase discriminator and a differential amplifier followed by a complex logic circuit that is finally mixed at the heterodyne.

The drawing below shows the wiring of the 7-pin socket marked 'MK.' at the top right. It is used for the connection of a handset, headset or another microphone/speaker combination. The colours are of the internal wiring when looking into the socket from the front panel of the device.

Connector MK - Handset

  • BAJ-13,5
    12V (13.5V) rechargeable battery
  • PT-6
    Transistorized mains power supply unit (PSU)
  • MK-1
    Handset (Mikrotelefonska kombinacija)
  • SL-1
  • TB-17
  • AT-17
    Long rod antenna
  • AT-18
    Wire antenna
  • AT-19
    Short rod antanna
  • KS-28
    Repeater cable
  • PS-11
    Carrying frame
  • ML-6
    Spinner (for winding wire antenna)
The radio is known under the following names:

  • RUP-12
  • UGAR-1
  • PD-7
  1. Unknown author, RUP-12 brochure
    Via Radista (Website) [1]. 3 March 1970. Retrieved April 2015.

  2. Unknown author, RUP-12 manual
    Via Radista (Website) [1]. 30 July 1970. Retrieved April 2015.

  3. Unknown author, RUP-12 schematic diagram
    Via Radista (Website) [1]. 1970. Retrieved April 2015.
  1. Radista, VHF Radio RUP-12 / 2K
    Website. Retrieved April 2015.
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