B5A1-PrK

B5A1-PrK antenna matching unit in the Prima-KV system

The B5A1-PrK is an antenna matching unit used as part of the Prima-KV airborne HF / decameter-band radio station. Its task is to match the output of the transceiver with the aircraft HF antenna so that the transmitter can operate correctly across the working frequency range. In an aircraft HF system, the antenna is usually short compared with the radio wavelength, so direct connection without a matching unit would give poor efficiency and unstable transmission. The B5A1-PrK solves this problem automatically and keeps the radio link usable on different selected frequencies.

HF antenna matching through B5A1-PrK

The B5A1-PrK works with capacitive-type aircraft antennas, including wire, cap-type and short whip antennas. These antennas are common on helicopters and transport aircraft, but their electrical parameters change strongly with frequency and installation layout. The matching unit adjusts the antenna circuit so that the Prima-KV transmitter sees the required load through the feeder line. This is especially important during transmission: if the antenna is not matched, output power is lost, the signal range drops, and the transmitter may operate under an unfavorable load.

B5A1-PrK location near the antenna input

The block is normally installed as close as possible to the HF antenna entry point. This is not just a convenient mounting choice; it is a radio-engineering requirement. A long high-voltage RF path between the matching unit and the antenna increases losses and can create insulation, interference and reliability problems. On Mi-8 family helicopters, the B5A1-PrK may be installed in the rear part of the cargo / passenger cabin, near the tail boom junction and rear fuselage frames, close to the external wire HF antenna connection.

B5A1-PrK installation on Mi-8 family helicopters

On Mi-8MTV-1, Mi-8AMT, Mi-171E and related helicopter versions, the B5A1-PrK is commonly used in Prima-KV installations or modernization programs replacing older HF radio equipment. The unit can be mounted on a dedicated shelf, equipment rack or structural frame area, depending on the aircraft modification and installation documentation. It is usually installed on a shock-absorbing PrK frame or related mounting arrangement to reduce vibration loads. The rear RF output is connected through an aircraft feedthrough insulator to the external HF antenna installed along the tail boom area.

Control and tuning operation of B5A1-PrK

The B5A1-PrK is not adjusted manually during every frequency change. It works automatically with the radio station control system and tunes the antenna circuit when a new frequency is selected. The switching of internal matching elements is performed through relay-controlled circuits, commanded by the radio station electronics. For the crew, this process is normally invisible: the operator selects the channel or frequency from the Prima-KV controls, and the antenna matching unit prepares the antenna path for transmission. Correct tuning is confirmed through system operation and, where applicable, control logic of the radio station.

Construction and operating conditions of B5A1-PrK

The B5A1-PrK is made in an unpressurized, dust-protected aircraft equipment housing. It uses natural cooling and does not require forced airflow, which simplifies installation and reduces dependency on separate cooling ducts. At the same time, the block must work in a vibration-loaded aircraft environment and in a wide temperature range. For maintenance, attention should be given to the unit housing, connectors, RF output, feedthrough insulator, mounting frame, shock absorbers and signs of overheating, contamination or arcing. HF matching equipment is sensitive to poor insulation and bad contact.

Identification and supply of B5A1-PrK

When ordering the unit, it is important to state the full designation B5A1-PrK and clarify whether the requirement is for the matching unit only or for a wider Prima-KV set. A complete radio station installation may also include the B1-PrK transceiver, B7P1-PrK control panel, PrK / B10A-PrK mounting frame and other installation parts. For replacement, the aircraft type, antenna type, radio station version and approved installation documentation should be checked. The condition, documentation, serial number, completeness and test status of the matching unit should be confirmed before shipment.

Product Type: Antenna matching unit / HF antenna tuner
Designation: B5A1-PrK
Radio Station: Prima-KV
Function: Automatic matching of the radio station transceiver output with aircraft capacitive-type HF antennas
Application / Where Used: Airborne HF / decameter-band communication systems
System / Installation Area: HF antenna circuit, near the aircraft antenna input / antenna feedthrough
Compatible Aircraft / Equipment: Mi-8MTV-1, Mi-8AMT, Mi-171E and other aircraft using Prima-KV radio station depending on approved configuration
Compatible Antenna Types: Wire, cap-type and short whip capacitive aircraft antennas
Frequency Range: 2.0000–29.9999 MHz
Frequency Step of Associated Radio Station: 100 Hz
Feeder-Side Input Impedance: 50 Ohm
Automatic Tuning Time: About 1 s average / up to 2 s depending on radio station version and tuning condition
Transmitter Power Compatibility: 100 W or 200 W depending on Prima-KV version
Control / Switching: Automatic control from the radio station; relay switching of matching elements
Digital Control Interfaces of Associated System: GOST 18977-79 / ARINC 429, RS-422 depending on radio station configuration
Power Supply: 18–31 V DC aircraft network, nominal 27 V
Construction: Unpressurized, dust-protected aircraft equipment block
Cooling: Natural cooling, no forced airflow required
Operating Temperature Range: −55 to +60 °C
Mounting: On PrK shock-absorbing mounting frame or aircraft equipment shelf depending on installation
Typical Installation Area on Mi-8 Family: Rear fuselage / cargo cabin area near frames 22–23 and HF antenna feedthrough, depending on aircraft configuration
Weight: Not more than 2.75 kg
Associated Blocks: B1-PrK transceiver unit, B7P1-PrK remote control panel, PrK / B10A-PrK mounting frame
Technical Documentation: Product passport, Prima-KV operating documentation, installation documentation and aircraft modification documentation as applicable

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Warranty
All products are covered by a standard 6-month warranty.
Extended warranty is available upon request and is agreed individually; it may affect the final product price.