Operation began with the Type T.3026 transmitter sending a pulse of radio energy into the transmission antennas from a hut beside the towers.
Each station had two T.3026's, one active and one standby.
The signal filled space in front of the antenna, floodlighting the entire area.
Due to the transmission effects of the multiple stacked antennas, the signal was most strong directly along the line of shoot, and dwindled on either side.
An area about 50 degrees to either side of the line was filled with enough energy to make detection practical.

The Type T.3026 transmitter was provided by Metropolitan-Vickers, based on a design used for a BBC transmitter at Rugby.
A unique feature of the design was the "demountable" valves, which could be opened for service, and had to be connected to an oil diffusion vacuum pump for continual evacuation while in use.
The valves were able to operate at one of four selected frequencies between 20 and 55 MHz, and switched from one to another in 15 seconds.
To produce the short pulses of signal, the transmitter consisted of Hartley oscillators feeding a pair of tetrode amplifier valves.
The tetrodes were switched on and off by a pair of mercury vapour thyratrons connected to a timing circuit, the output of which biased the control and screen grids of the tetrode positively while a bias signal kept it normally turned off.

Stations were arranged so their fan-shaped broadcast patterns slightly overlapped to cover gaps between the stations.
However, it was found that the timers sending the broadcasts could drift and the broadcasts from one station would begin to be seen at others, a problem known as "running rabbits".
To avoid this, power from the National Grid was used to provide a convenient phase-locked 50 Hz signal that was available across the entire nation.
Each CH station was equipped with a phase-shifting transformer that allowed it to trigger at a specific point on the Grid waveform, selecting a different point for each station to avoid overlap.
The output of the transformer was fed to a Dippy oscillator that produced sharp pulses at 25 Hz, phase-locked to the output from the transformer.
The locking was "soft", so short-term variations in the phase or frequency of the grid were filtered out.

During times of strong ionospheric reflection, especially at night, it was possible that the receiver would see reflections from the ground after one reflection.
To address this problem, the system was later provided with a second pulse repetition frequency at 12.5 pps, which meant that a reflection would have to be from greater than 6,000 miles (9,700 km) before it would be seen during the next reception period.
Operation began with the Type T.3026 transmitter sending a pulse of radio energy into the transmission antennas from a hut beside the towers. Each station had two T.3026's, one active and one standby. The signal filled space in front of the antenna, floodlighting the entire area. Due to the transmission effects of the multiple stacked antennas, the signal was most strong directly along the line of shoot, and dwindled on either side. An area about 50 degrees to either side of the line was filled with enough energy to make detection practical.
The Type T.3026 transmitter was provided by Metropolitan-Vickers, based on a design used for a BBC transmitter at Rugby. A unique feature of the design was the "demountable" valves, which could be opened for service, and had to be connected to an oil diffusion vacuum pump for continual evacuation while in use. The valves were able to operate at one of four selected frequencies between 20 and 55 MHz, and switched from one to another in 15 seconds. To produce the short pulses of signal, the transmitter consisted of Hartley oscillators feeding a pair of tetrode amplifier valves. The tetrodes were switched on and off by a pair of mercury vapour thyratrons connected to a timing circuit, the output of which biased the control and screen grids of the tetrode positively while a bias signal kept it normally turned off.
Stations were arranged so their fan-shaped broadcast patterns slightly overlapped to cover gaps between the stations. However, it was found that the timers sending the broadcasts could drift and the broadcasts from one station would begin to be seen at others, a problem known as "running rabbits". To avoid this, power from the National Grid was used to provide a convenient phase-locked 50 Hz signal that was available across the entire nation. Each CH station was equipped with a phase-shifting transformer that allowed it to trigger at a specific point on the Grid waveform, selecting a different point for each station to avoid overlap. The output of the transformer was fed to a Dippy oscillator that produced sharp pulses at 25 Hz, phase-locked to the output from the transformer. The locking was "soft", so short-term variations in the phase or frequency of the grid were filtered out.
During times of strong ionospheric reflection, especially at night, it was possible that the receiver would see reflections from the ground after one reflection. To address this problem, the system was later provided with a second pulse repetition frequency at 12.5 pps, which meant that a reflection would have to be from greater than 6,000 miles (9,700 km) before it would be seen during the next reception period.
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