SE-212: TL BBC

Tragbar Leichte Funkstation BBC (Portable Light Radio Set BBC), SET 2/10 resp. SE-212; produced by Brown Boveri.

For the ground - to - air communication of the Air Force, Brown Boveri Cie. developed the portable light radio station TL BBC , it got the internal company designation SET 2/10. The developers of the set were inspired by the TL developed 8 years before, as the dimensions the technical specifications are concerned.

Technical Data

Principle: Transceiver, Receiver: Single conversion, IF 1600 kHz
Modes: A1 (CW), A2, AM (A3)
Frequency range: 4,6 - 15 MHz (two ranges 4'600 - 9'000 / 9'000 - 15'000 kHz, dial accuracy around 10 kHz)
Sensitivity: AM (A3) / Selectivity:
Output power A1 12 W, A2/A3 15 W (medium power 1,6 or 2 W; low power 0,28 or 0,35 W)

Power Supply

Accumulator / Batteries: Accumulator for heaters and to generate the plate voltages of the receiver valves by use of a vibrator power supply (for reception mode only)
Generator: pedal generator to generate the heaters, plate and grid bias voltages for reception and transmission mode.
Mains: a Mains power supply was added later to the station equipment.

For receiving operation, the station only needs 6 V DC from the heaters accumulator, the plate voltage is generated from a vibrator power supply (with vibrator NSF 32/2 HT 6 mB) in the accessory case. For transmitting, 8.8 V heaters voltage, 330 V plate voltage and 65 V grid voltage are required, all these are generated by the pedal generator.

The heaters battery consists of five elements, which are wired in series to gain the 6 V heating voltage, the capacity of the accumulator is 13 Ah.

Dimensions

Apparatus Case 23 kg
Accessories Case 24 kg
Treadmill generator 23 kg
Antenna poles and spares bag, 7 kg each

Accessories

Standard antenna is a 8 m vertical antenna with star-shaped counterpoises. When used on higher frequencies, the antenna length can be reduced to 6 m height using only six elements.

The antenna is to be connected to the „Antenne“ jack for frequencies below 10 MHz and to the „Bodenantenne“ jack for frequencies above 10 MHz, the counterpoise for the radials is connected to the other jack.

Operation

The transceiver is tunable in two ranges from 4.6 to 15 MHz, the dial accuracy is about 10 kHz. The two dials are arranged spirally on a round dial. When the band switch is used, the dial pointer is moved to the corresponding frequency dial. The „receiver adjustment“ is used to fine tune the other station in alternate traffic.

Similar as found in Zellweger sets, there is a combined main and mode switch, turning to the left activates A1 telegraphy, the volume is increased wehen the control is turned to the left, turning to the right via the off position activates the A3 / AM mode and lets the volume increase.

The transmission power can be switched in three steps from 0.35 to 15 watts, a simple antenna tuning circuit is used to tune to maximum antenna current. As found in other sets from the same years, the meter can be switched to display heaters and plate voltage (red or blue switch position and meter marks).

Technical Principle

The receiver acts as single conversion with a RF amplifier stage; the signal is converted in the mixer stage to an IF of 1600 kHz. After two IF amplifier stages (KF4), e smiconducter diode is used for the demodulation, followed by an AF amplifier stage.

In the transmitter, the audio frequency signal coming from the crystal microphone is first amplified (KF4, KF4) when a carbon microphone is in use, one of the AF stages can be switched off. If modulated telegraphy A2 is used, a 1000 Hz sound generator is activated, this is also used for the sidetone in telegraphy. A valve EL2 in a Hartley oscillator circuit is used as main transmitter oscillator. When modulated tone telegraphy (A2) is used, the plate voltage is modulated by the soun oscillator. In the case of continuous wave telegraphy, keying acts on the screen grids of the transmitter output stage valves. Since these work under maximum load when the maximum output power is selected, the tubes had to be replaced quite frequently.

After loosening six screws with red markings, the chassis can be pulled out. It consists of a upper and a lower part, an oscillator unit connected to the rotary capacitor and the dial mechanism. On a terminal block, there are 25 plugged connections between the upper and lower part, only a RF cable is soldered.

Valve Layout

Transmitter: V7 (EL2, transmitter oscillator in Hartley circuit); V8, V9 (two EL2, transmitter final stage); V12, V13 (two KF4, mikrophone amplifier); V10, V11 (two EL2, modulator stage, plate modulation using a modulation transformer).

Receiver: V6 (KF4, RF amplifier); V5 (KF4, oscillator and mixer), V4, V3 (two KF4), 1st and 2nd IF amplifier), semiconductor diode for demodulation; V2 (KF4, AF amplifier); V1 (KF4, BFO for A1 reception).

A meter test switch is used to check the heaters voltage of the tubes, which should normally read 2 V. In case of a defective tube 0 V are displayed, if the second valve indicated is defective, the double voltage or 4 V are read from the meter. The tube heaters voltages in the transmitter and receiver circuits are stabilized by two iron-hydrogen resistances.

Development

As an addition to the TL, Brown Boveri developed for the Aircraft units a shortwave radio set, that covered a much higher frequency range. For the aircraft signal companies, a total of 73 (or 74) stations were ordered. According to the documentation „Funkstationen der Armee“ theprice of one was 11'000.- Fr.

Field Use

Initially, the „TL BBC“ was used for the communication between ground units of the Air Force. After 1946, they were used for command communication of the heavy anti-aircraft detachments. Soon, it turned out, that the frequency range and the antenna was not well suited for ionospheric propagation, so the radio set was soon withdrawn and allocated to the war reserve after 1951.