SE-227

Army radio set SE-227, American original designation AN/PRC-77; manufactured by different contractors of the Associated Industries.

In parallel to the frequency-modulated VHF transceiver SE-412, the portable set SE-227 operating in the same military VHF band was introduced. The set of American provenance saw a widespread use in the NATO countries under it's original designation AN/PRC-77.

Specifications

Principle: Transceiver, Receiver: Single conversion, IF 11.5 MHz
Modes: FM (F3)
Frequency Range: 30-52.95 (A band) and 53-75.95 MHz (B band), 920 switchable channels with 50 kHz channel spacing
Sensitivity: AM (A3) / Selectivity:
Output power: 1 - 3 Watts

Power Supply

Accumulator / Batteries: 15 V special battery
Power Supply: 24 V (12 V with a special converter) with vehicle power supply unit OA-3633

Dimensions

280 x 102 x 230 mm, 11.7 kg

Accessories

As standard antenna, the AT-892 portable antenne (whip antenna, length 90 cm), an AT-271A antenna (whip antenna, 3 m) or an AS-1729 vehicle antenna (whip antenna, 3 m) was used.
As an alternative, a groundplane long distance antenna FA-227/412 with a 2.45 m high vertical radial on a 4 m mast could be used. The long distance antenna material is stowed in a 110 x 200 x 12 mm canvas bag, with a weight of 9.1 kg.
The relay equipment consists of a 15 m cable stowed in a canvas bag with corresponding multi-pin connectors and connection boxes to connect two SE-227 sets to perform as relay station.
To control the SE-227 from a remote location, for example from a shelter, the Remote Control Equipment BFA SE-227/412 is used. The local unit is connected to the SE-227 AUDIO input and the remote unit is connected over a conventional duoble wire field telephone line.

Operation

The fully solid state transceiver can be used as a manpack set, as a vehicle station, remotely controlled or as a relayn station. The version used in the Swiss Army carrying the designation SE-227 is mounted on a carrying frame with an accessory pocket (with microphone, antenna material, noise headset, antenna test lamp), which also offers enough space for a spare battery.

The radio set covers the military VHF range in two bands (30 - 52.95 and 53 - 75.95 MHz) in 50 kHz channel spacing. In FM telephony, the ouput power is 1 - 3 Watts. When the 90 cm metal band antenna is used, communications range is up to 3 km; with the 3 m vehicle whip antenna up to 12 km.

As a manpack radio, the SE-227 is powered by a 15V dry battery which should last for 40 hours in normal operation. The OA-3633 power supply unit can be powered by 24V and, if an additional voltage converter is used, also by a 12V vehicle battery; the power supply unit is equipped with an audio amplifier and loudspeaker as well.

On the front panel you will find the external power socket, the antenna connector for the portable antenna and a socket for a 50 ohm coaxial antenna output at the left side.

First, according to the desired operation frequency, the band A (30-52 MHz) or B (53-75 MHz) has to be selected with the switch on the left side of the front panel. Between the two knobs for frequency selection, the frequency is displayed on a mechanical digital display. Two operation channels can be preset mechanically, since the procedure must be handled differently for frequencies in the two different bands, the technical regulations should be consulted.

On the right side of the front panel, below the microtel (AUDIO) connectors, the volume control and the power switch are located. With the SQUELCH activated, an audio frequency subchannel (and thus inaudible to the user) with a 150 Hz signal is transmitted and opens the squelch on the corresponding station. Switch position RETRANS activates the relay mode and LITE the dial illumination.

Technical Principle

In Reception mode, the signal has to pass the antenna tuner circuit, the antenna transmit-receive relay and two RF amplifier stages. In the mixer stage, it is mixed with the signal of the local oscillator active between 41.5 and 64.45 MHz to generate the IF of 11.5 MHz. After five IF amplifier stages, the signal is fed to the limiter (to eliminate unwanted AM components) and is demodulated in the discriminator. An AF amplifier feeds the output to the headphones jack. The 150 Hz squelch automatically opens the receiver, when a subaudible 150 Hz squelch tone is transmitted.

In transmit mode, the audio signal from the microphone is filtered and amplified, alternatively the signal from the wideband input (for encryptes communication) or the 150 Hz squelch tone is added. Then the signal has to pass the modulator stage. Here, the 11.5 MHz signal is modulated and fed via a buffer amplifier to the signal of the receiver oscillator to generate the final RF signal. The RF signal is fed to the driver stage and the transmitter output stage, from there to the receive - transmit relay and over the automatic antenna tuning circuit to the antenna output socket.

The inside of the device is accessible, after the four screws that run from below the carrying handles to the front are loosened, then the chassis can be pulled out.
After releasing three black marked screws, the upper circuit board can be flipped to the side and gives access to the chassis below.
The device is of modular construction to simplify repairs.

Semiconductor layout

The transceiver is completely „solid state“.

Development

The frequency-modulated FM radios AN/PRC-8 /-9 /-10 were introduced with the US units in 1951 and saw wide use in the Korean War. There sets were replaced in 1962 by the AN/PRC-25. This transistorized manpack radio was much lighter, than the hollow state (valve) predecessor, but in the final output stage, still two 2DF4 tubes were used. In the late sixties, the was redesigned with a solid state RF power amplifier and in this version, it was acquired as manpack radio as a temporary solution by the Swiss Army, it got the designation SE-227. These sets could easily communicate with the vehicle station AN/VRC-12 resp. SE-412.

Actually, in the sixties, is was planned to replace the tube-equipped radios SE-206/9 by the new SE-225 („Project Peter“), which was under development after 1966. Its development was delayed due to the transition from valve to transistor and integrated circuit technology. The wish to introduce channel bundling technology and integrated speech scrambling, caused an even longer delay.

So the „Vietnam Radio“ PRC-77 was introduced as a temporary solution to cover the urgent demand for a solid state set. This temporary measure was one of the longest lasting „temporaries“ in the history of the Swiss signal troops, since from the introduction of the AN/PRC-77 around 1968 until 1990, a total of 12243 units were acquired.

The manpack transceiver SE-227 system often came equipped with the OA-3633/GRC power supply / car mount, a mounting frame with built-in power supply and speaker to be used as a vehicle station (US designation AN/VRC-64).

The device head already a provision to connect a voice encryption device, in 1984 the SVZ-B , the digital „voice scrambler broadband“ was introduced. Until then, the Swiss signalmen had to communicate without electrony encryption, using battle code lists and „disguised language“.

Field Use

The SE-227 was used in different configurations between 1971 and 2003; for over 30 years, this set was the backbone of the tactical military communication of the Swiss Army. It had the disadvantage that communication was unencrypted, and is saw a widespread use as a manpack and vehicle radio even before the introduction of the „classified“ SVZ-B in 1984.

The radios were used as tactical command sets and for technical and service communication within the divisions, battalions, companies and down to platoon level.

After 2002 to 2007, the sets were liquidated and some were sold demilitarized (since the use of the military VHF band is not allowed to civilians, the transmit-receive relay was removed) and delivered to collectors like that.