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Ampliphase BTA-50H



Ross Revenge Ampliphase BTA-50H

On entering the Ross Revenge transmitter room your are immediately drawn towards the largest of the the three transmitter cabinets, the Ampliphase BTA-50H, 50kW transmitter.

The 50kw transmitter, together with two additonal 10kw transmitters, were sourced by Radio Caroline's transmitter engineer, Peter Chicago, during September 1981 as part of the Ross Revenge / Radio Caroline fit out. Purchased from Besco International in Dallas, USA - the three units were shipped to Spain for Peter to install and test whilst the ship was being converted.

Ross Revenge Inside the BTA-50H (1)
BTA-50H - How Did It Operate ?
We could probably fill 10 pages explaining how the Ampliphase operated but in essence its operation can be simplified in 5 steps;

1 - The system takes an audio signal from the broadcasting studio [the carrier] and splits it into two identical signals.

2 - The signals are first phase shifted 135 degrees from each other to provide a base power output with zero modulation from the transmitter.

3 - Each signal is then is then phase modulated by the audio signal, with one signal being positively phase modulated and the other signal being negatively phase modulated.

4 - The two signals are then amplified to the required power output via a process of different stages within the Ampliphase cabinets.

5 - Finally the two signals are summed together in the final output filter stage of the transmitter (the point at which they are transmitted via the Tx Mast)
Ross Revenge Inside the BTA-50H (1)
The History of Ampliphase
Contrary to popular belief the Ampliphase system was not originally created by RCA, but by McClatchy Broadcasting, a group of AM | FM & TV Stations based in California. The original Ampliphase design in 1935 by Henri Chireaux, termed outphasing, was sold by McClatchy to RCA. Once RCA had aquired the Ampliphase design this enabled them to create their legendary 50,000 watt - 10,000 watt and 5,000 watt models that can stil be seen onboard the Ross Revenge.

Unlike other most other commercial AM transmitters Ampliphase did not require modulation transformers or modulation reactors which offered huge savings on the initial cost - the downside to this being that the units required more of a maintenance input.

In principle the Ampliphase concept traded lower capital cost against higher running costs .... whilst still achieving a modest improvement in efficiency.

See Also
Ampliphase Terminology
Henri Chireix

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RCA BTA-5G (5kW Transmitter) | Radio Caroline / Radio Monique Diplexer