Radio relay device HVT-1

Radio relay device HVT-1 was produced in the late 1950s at the "Iskra" factory in Ljubljana. It was generally the primary RRU in infantry regiments, while in higher units and commands it served for "cross" links. It was installed in the field vehicle Zastava AR-55V with Zastava D-2V semi-trailer with a capacity of 0.5T. Depending on the purpose (terminal or RR repeater station) and multi-channel telephone devices with carrier frequency, several systems are distinguished: HVT-1, HVT-4, HVT-12 and HVT-14.

Radio relay device HVT-1 consisted of the following components: transmitter HD-1, receiver HP-1, service channel block HK-1, two helical antennas AS-1 with antenna mast and accessory boxes. In addition to the HVT-1 device, the complete HVT-1 radio relay system also included a petrol generator AG-3, necessary cables, cable reels, tools and accessories.

The radio relay transceiver operated in the frequency range from 1700 to 2300 MHz. The operating frequency was selected manually (continuously), with the aid of a built-in frequency meter. The modulation is pulse frequency with a mean pulse repetition frequency of 80 kHz (12.5µs) and a pulse width of 1.8µs. The spacing between the transmit and receive frequency of one radio relay station had to be at least 80 MHz, while the spacing between the receive or transmit frequencies of parallel radio relay lines had to be at least 10 MHz.

The transmitter output power in pulse mode was 20W and could be reduced by a dummy load by 10 dB, i.e. by a factor of 10. Range is expressed as a transmission value and was a maximum of 163 dB. In general, the distance between radio relay stations was not to exceed 50 km. At the terminal station, a multi-channel telephone device (carrier frequency device - UNF), usually FNT-15, was connected to the radio relay device. The high-frequency channel range (modulation frequency band) of this device had to be from 3.6 kHz to 23 kHz, and the service channel from 300 Hz to 2600 Hz. The device was powered by 220V AC from a petrol generator AG-3 or from the electrical grid. Origin: Yugoslavia.

Radio relay device RDM-63

To equip infantry battalions with a radio relay device for communications toward the command of the superior regiment, the Communications Directorate purchased in the 1960s from the Czechoslovak factory "Tesla" Přelouč a single-channel RR device RDM-63. The complete device set was delivered in a wooden crate into which, along with the transceiver, all other components were packed. The crate also served for transport: by hand, pack animals or motor vehicle.

The RDM-63 carried a single telephone channel, with a service communications link between operators enabled. It was usually connected to the battalion induction telephone exchange (MP-10). It operated in the frequency range from 235 MHz to 260 MHz with frequency modulation, achieving an output power of 100 mW. It was powered by 6V DC from lead-acid batteries. Link security was achieved through the device's low output power and the use of directional Yagi antennas. It did not remain in JNA service for long, as it was replaced by the domestically produced single-channel radio relay device RRU-1. Origin: Czechoslovakia.

Radio relay device RRU-1

Radio relay device RRU-1 was produced by "Iskra" from Ljubljana in the early 1980s, and after completing laboratory and field trials in 1983 it was included in the equipment of signals units. The RRU-1 replaced the Czechoslovak RDM-63 and became the primary radio relay device of the infantry battalion. It was used to transmit a single standard telephone channel (300–3400 Hz) duplexed, or data at modest rates of 1.2 or 2.4 kb/s using an appropriate modem. In addition to this channel, it also had a service telephone channel. It could be set up for operation from the operator's back, a signals vehicle, a shelter, a tent, in the open or as a stationary device in a building.

The RRU-1 device operated in the VHF band in two sub-bands, "A" from 235 MHz to 260 MHz and "B" from 245 MHz to 270 MHz, with frequency modulation deviation of 10.5 kHz. The frequency was set by switches, with a channel spacing of 25 kHz. A synthesizer regulated the operating frequency accuracy. The spacing between the receive and transmit frequency was always 10 MHz. The transmitter emitted at an output power of 0.5W, radiated by whip antenna AT-46 or directional Yagi antenna AT-47. The device range on flat terrain with the whip antenna was up to 5 km, and with the Yagi antenna mounted on 6-metre antenna mast SA-10 up to 30 km. When greater range was needed, or (more commonly) due to terrain obstacles, up to two radio relay repeater stations could be formed, giving a range of up to 90 km. A radio relay repeater station was formed from two RRU-1 devices. Depending on whether the device operated as stationary or portable, it was powered from the 220V/47-60Hz electrical grid, an external DC source of 12V to 30V, or its own NiCd battery 12V/6Ah.

Radio relay device RRU-1 was manufactured using semiconductor technology. Electronic components are housed on six separate sections (modules), with each section forming a complete subassembly. The sections connect via connectors to the front panel, which is enclosed in an aluminium housing. The RRU transceiver contained the following sections: receiver E0002, transmitter E0001, synthesizer E0003, telephone section E0004, antenna switch E0005 and PGS section E0006 (20V converter, line call generator, 9.6V stabilizer). The receiver was a double superhetrodyne with first intermediate frequency of 21.4 MHz and second at 455 kHz. The synthesizer operated on the principle of indirect synthesis, and frequency modulation of the AF signal in the transmitter was performed on a voltage-controlled oscillator (VCO) whose signal was further amplified to an output power of 0.3W.

The complete RRU-1 device set included: transceiver, rectifier block IB-220/12, 2 NiCd batteries 12V/6Ah designated AB-12/7, carrying frame, whip antenna AT-46, Yagi antenna AT-47, antenna mast SA-10, connection box KP-34, handset combination and headset with microphone and chest switch, 2 antenna cables KK-59 and KK-60 with reels, 2 canvas bags TB-75 and TB-76, as well as other power and connection cables and spare accessories and tools. The complete set weighed 43.5 kg.

The RRU-1 was a very simple device to operate and maintain and was therefore popular among radio relay operators. Relay communications could be established through it in a very short time. On the other hand, information frequently leaked through this device as it was easily intercepted. Its Yagi antenna had a very wide radiation angle (56° to 74°), and the telephone channel carried over it was most often unencrypted, which undisciplined users paid no attention to. Origin: Yugoslavia

The SFRY State Secretariat for National Defense, around 1960, procured the modern and high-quality radio relay device FM-800, produced by the well-known German corporation "Siemens". At the time the import decision was made, in addition to West Germany, several European NATO members were already equipped with this device, which was decisive in its selection. It received the Yugoslav designation RRU-800. It equipped stationary and mobile communications centers of JNA operational and strategic units. To be included in the mobile radio relay communications system, it was initially installed exclusively in the domestic field vehicle Zastava AR-55/V 4x4 with semi-trailer Zastava D-2V 0.5T. Two complete sets (systems) were formed, designated RRU-800/II (terminal radio relay station) and RRU-800/III (radio relay repeater station). They differed from each other only in the composition of their sets. In addition, besides vehicle transport, the regulations of the time provided for transport of this device by pack animals and, over shorter distances, by personnel.

Radio relay device RRU-800 was used to transmit up to 24 frequency-division multiplexed telephone channels in the range from 4 kHz to 108 kHz, provided by a multi-channel carrier frequency telephone device (initially the domestic FNT-7, and later the Siemens VZ-4/12 and VZ-12K), over distances up to 50 km. When there was no line-of-sight between terminal stations, or when their mutual distance was large, a maximum of 12 radio relay repeater stations were placed on a single line.

The device operated in the frequency range from 610 MHz to 960 MHz, with the operating frequency set manually and continuously, while the automatic control regulates the frequency within ±400 kHz of the operating frequency. The spacing between the receive and transmit frequency when operating with a shared antenna (basic operating mode) had to be at least 40 MHz. The receiver frequency must not be higher by 50, 75 or 100 MHz than the transmitter frequency. Modulation is frequency modulation with maximum deviation: for 4-channel operation ±45 kHz, 12-channel ±14 kHz, and 24-channel ±10 kHz. The transmitter output power was approximately 10W, obtained from two Siemens UHF transmitting triodes 2C39BA. This power was radiated by a double helical antenna with gain ranging from 12.5 dB to 15.9 dB depending on frequency. The antenna was mounted on antenna mast SM-17 with a maximum height of 17 metres.

Radio relay device RRU-800 was connected four-wire to the carrier frequency device (UNF) using shielded cable CX-1065/G (later the domestic KS-140), with a maximum separation of up to 4 km. The output level to the UNF was 0 dB, and the input from the UNF was 0 dB to -9 dB. It was powered by 220V or 110V/47-63Hz AC from the electrical grid or petrol generator AG-3, of American origin, with a power of 2 kW, consuming 350 VA.

The RRU-800 was built using waveguide and vacuum tube technology and represented a complex electronic instrument that could only be operated by well-trained soldiers of the radio relay specialty or professionals, which is why they were considered the elite among "radio relay operators".

The complete device set was stored in 4 metal cases, which were hermetically sealed with lids during transport. In the first three cases, the UHF, amplifier and rectifier block chassis were secured via rubber shock absorbers, while in the fourth case accessories, tools and spare parts were packed. Antenna mast SM-17 was procured separately. During transport it was packed in three metal frames and a canvas bag, while two coaxial antenna feeders of 7m and 18m were wound onto a common reel.

The UHF block was stored in the case marked "I". It contains the UHF parts of the transmitter and receiver, as well as a test oscillator. It was built using waveguide technology and designed so that the transmitter controls and assemblies are on the left side, and the receiver and test oscillator on the right. It was connected via multi-conductor cables to the amplifier and rectifier blocks. The antenna was also connected to this block via the antenna cable.

The amplifier block was stored in case "II". It contained the intermediate frequency and low-frequency modules of the transmitter and receiver: IF amplifier, receiver amplifier, pilot group I module, transmitter amplifier, speech amplifier, pilot group II module, and service channel module. The modules were clearly separated and easily accessible from the front for adjustment, tube replacement or repair. The amplifier block was connected by cables to the UHF and rectifier blocks.

The rectifier block was located in case "III". It provided all the necessary voltages for the operation of the electronic circuits. It consisted of an upper rectifier section for powering the amplifier block and a lower rectifier section for powering the UHF block. These voltages were carried to the UHF and amplifier blocks via two multi-conductor cables. The rectifier block was connected to AC voltage from the electrical grid or generator.

The accessories case "IV" was used for storing, protecting and transporting accessories, tools and spare parts. All components inside were secured and thus protected during transport. Case "IV" was packed with: the disassembled antenna (2 helical radiators, 2 antenna reflectors, radiator mount, antenna junction and 2 coaxial cables of 1m length), handset combination, connecting cable box, spare tubes box, spare parts box, tools, metal stand PS-3, coaxial and multi-conductor cables for interconnecting blocks and power cables.

Radio relay device RRU-800 remained in JNA service until its dissolution in 1991. It coexisted in parallel with newer generation devices FM-200 and RRU-9B. It underwent numerous modifications so that, in addition to the original versions RRU-800/II and RRU-800/III on the AR-55V vehicle with 0.5T semi-trailer, two new systems were formed:

- RRS-800/1 - terminal radio relay station. Located in the Pinzgauer 710K field vehicle, with the AG-3 generator replaced by the domestic AB-1.5 generator. Two systems formed a radio relay repeater station.

- RRVS-800/12 and RRVS-800/24 - terminal radio relay station with one or two UNF VZ-12K respectively. The system was installed on the TAM-5000D field truck. Power was provided by the domestic diesel generator AD-3.7. Origin: West Germany.

Radio relay device FM-200

In order to modernize the radio relay component of the communications system, the JNA imported in 1975 a high-quality NATO device, produced as a joint product of West German companies AEG Telefunken and Siemens AG. This device, designated FM-200, was intended to replace the then-obsolete RRU-800 (also produced by Siemens), which formed the backbone of radio relay communications in operational and strategic units.

Radio relay device FM-200 was used to transmit information in analog and digital form in the frequency range from 610 MHz to 960 MHz. The spacing between the receive and transmit frequency had to be greater than 27 MHz. The transmitter output power was 10W, provided by two well-known Siemens transmitting ceramic triodes 2C39BA. It provided transmission of 4, 12 or 24 frequency-division multiplexed telephone channels in the range from 6 kHz to 108 kHz (FDM), or up to 32 time-division multiplexed channels (TDM) at data rates of 256 Kb/s, 512 Kb/s and 1024 Kb/s. The device range, with "line-of-sight", was, as with other radio relay devices, up to 50 km. To achieve greater range, a radio relay route was formed with multiple radio relay repeater stations, each consisting of two FM-200 devices.

Upon purchase, in order to save costs, an insufficient number of TDM devices (devices with pulse code or delta modulation) were procured, so initially the FM-200 was connected to one or two Siemens 12-channel carrier frequency devices (UNF) of the older generation (type VZ-12K) and used exclusively for transmitting frequency-multiplexed telephone channels. This significantly degraded the capabilities of the FM-200 radio relay device and set it back a generation. Later, the necessary TDM devices were imported, and domestic devices were also produced.

The device was powered by 220/110V AC from the electrical grid or generator, or by backup power from 24–28V DC provided by lead-acid batteries. In the event of an AC power failure, the device automatically switched to backup power and returned to grid power when it was restored, so there was no interruption of the radio relay link.

The complete FM-200 device set, purchased from the manufacturer, had three separate blocks (RF block, system block and rectifier block). The blocks were secured by shock absorbers to a steel frame which was used for assembly and easy carrying of the device. Also supplied were a multi-dipole directional antenna, servicing accessories, various cables for signal interconnection and power distribution cables. This set was sufficient for operation from a stationary installation, where a shared antenna mast was used for mounting the antenna. For independent operation, the Clark-73 antenna mast from Clark Masts was separately purchased for antenna deployment.

RF block (IV) was located at the top of the assembly frame and its task was to amplify the signal of 50–100 mW received from the system block to 10W in the transmit direction and forward it to the antenna via the antenna cable. In the receive direction, the received signal, after the duplexer and receive filter, was amplified in a low-noise amplifier and forwarded to the system unit. System block (II), located in the middle, essentially represented a complete radio relay device, as it performs full signal processing up to the operating frequency and power of 50–100 mW. Rectifier block (I) provided all necessary voltages for the operation of the system and RF blocks. Multi-dipole directional antenna was adapted for operation across the entire frequency range of the device. The antenna had a fairly wide radiation angle, so it was easy to aim it toward another participant. It was mounted on the CLARK-73 antenna mast, which was exceptionally easy to operate (only two operators were needed to raise it) or on the light antenna mast (LAS) of domestic production.

For inclusion in the mobile communications system, the FM-200 radio relay device was installed in field vehicles, thus forming radio relay systems. The following systems of this device existed, depending on their purpose:

- terminal radio relay station RRS-200/1. Installed in the Pinzgauer 710K field vehicle. The complete set of this system consisted of: FM-200 radio relay device - complete set, CLARK-73 antenna mast, VHF radio device RU-2/1, pulse regenerator TlRgI-1, induction telephone M-63, petrol generator AB-1.5-230 and various cables, engineering tools and accessories. The crew consisted of 3 members.

- radio relay repeater station. Installed on several types of field trucks. Depending on the vehicle, such systems carried the designations: RRS-200/2 (field truck 5t, 4X4, TAM-5000D), RRS-200-2 (field truck 1.5t, 4X4, TAM-110 T7 BV) and RRS-200-2/1 (field truck 3t, 6X6, TAM-150 T11 BV). The complete repeater station set consisted of: two complete FM-200 device sets, CLARK-73 antenna mast, light antenna mast LAS, VHF radio device RU-2/1, pulse regenerator - telephone TlRgl-1, induction telephone M-63, diesel generator AD-3.7-230, lead-acid batteries for continuous power supply, cables and other accessories, engineering tools and quartermaster equipment. The system crew numbered 4 members.

Due to the quality of the device, the FM-200 radio relay device was also procured by the police in the late 1970s. Guided by experience, they also purchased TDM devices from the same manufacturer and made maximum use of all the advanced digital information transmission capabilities. They used it as a stationary device or installed it in a Land-Rover field vehicle, TAM-110 truck and TAM-150 truck, thus forming mobile radio relay stations.
Origin: West Germany.