Carphone 1965
On the 5th July 1965 the London Radiophone service was offically opened.
After 6 months it had 300 subs, when no more subs were accepted
It was replaced in 1972 by System 3 (or did they run in parallel in london for a period ?)
Most of the details below were gleaned from POEEJ July 1966 and from A PYE radiophone service manual thanks to Ron Sewell
Transmitters at Pimlico( kings langley),Kelvedon Hatch( Brentwood) and Beulah Hill (crystal palace),
Pictures of mobile equipment at http://www.qsl.net/gm8aob/pages_2/lc10fm.htm#LC10FM
Air Interface Specification
10 Channels with a Spacing of 50 Khz FM deviation +- 10 Khz (but in the 1966 article described as 25 Khz)
Land Station 35w, mobile Station typical 12-15w
Each radio capable of tuning to 10 channels (1 calling for the whole of greater London,3 for traffic at each Transmitter
Selective calling by means of 4 digit code, signalled with 600Hz and 1500Hz tones on the calling channel transmitted from all 3 sites simultaneously
Mobiles alert the operator that they want to make a call with a short burst of 2060 Hz tone on a free traffic channel
Its strange that the POEEJ article says ...
The frequency allocations to the base stations have been determined by the need to avoid the possibility of intermodulation interference either with other radiophone channels or with private mobile services, operating in adjacent frequency bands. In common with private services, an overall channel spacing of 25 kc/s has been adopted. However, by limiting the minimum channel spacing at any one station to 50 kc/s, suitable channel allocation has made it possible to permit a higher peak modulation deviation. Phase modulation is employed, resulting in a maximum deviation of ± 10 kc/s in contrast to the ± 5 kc/s to which 25 kc/s channelling systems are normally limited. In this way a signal-to-noise advantage of some 3 db is obtained.
But the Pye manual says 50 Khz channel spacing
Was it important politically to say the service was on a "modern" and spectrum efficient 25 Khz spacing ??
Incoming call
1968 London Code Book
The calling party would dial 140,
When the radiophone operator in Tate Gallery Telephone exchange, receives a call for a radio phone. She plugs into the "common outgoing jack", This:-
1) Turns the three transmitters on at each base station,
2) Starts the "selective calling encoding" circuitry.
3) Connects the audio output of the "selective calling encoding" to the input of all three transmitting stations
4) A little later the "ready to start" Supervisory light will dim, indicating to the radio phone operator that she can now dial the car phones code 4? digit code
5) The digits along with an embedded synchronisation signal are sent using 600 Hz and 1500 Hz tones
The "ready to start" supervisory returns to full brightness ?
Once the code has been sent the radiophone operator can withdraw the plug from the "common out going jack"
The tones are received by all radiophones that are in range and switched on at the time.
If the code encoded in the series of tones matched with that of the radiophone,the radio phone then buzzes and the "CALL" lamp illuminates. The picture on the right kindly taken by Ron Sewell is the Scantlin decoder unit that drives the light and buzzer
The 1972 POEEJ article says "A 10 second period is required to call the mobile subscriber"
The subscriber then needs to press the "CALL" button to let the operator know he can take the call.
The radio phone will then transmit a 2060 Hz tone on the calling channel (159.55Mhz ), and continue to do so for between 5 and 12 seconds after the "Call" button is released.
At each base station that the tone from the radio phone is received on a strong enough carrier, a signal is sent back to the operators position, to light the "CALL - LAMP" near the answering jack for Brent Wood, or Pimlico or Crystal palace (or maybe more than one).
The operator will then plug into one of the stations answering jacks, just that base station will then transmit her voice to the subscriber. When he wants to speak to her he needs to press the "Push to Talk" Button, which switches the antenna away from the receiver to the transmitter, the transmitter is enabled and sound from the microphone is transmitted on the selected channel
The operator will then select a free channel on an appropriate base station and tells the subscriber which channel to switch to.
The subscriber will select that channel, then either
1) Because the handset is still off the hook ( and the traffic channel is free), the radio phone starts transmitting carrier immediately the subscriber presses the PTT button,The operator plugs into the answering jack as soon as she sees the "channel engaged" lamp glow, and continues speaking to the operator again on the new (traffic) channel she then connects him to person who called him
or
2)The subscriber needs to press the call button again
The radiophone will then transmit a 2060 Hz tone on the traffic channel ), and continue to do so for between 5 and 12 seconds after the "Call" button is released.
If the operator has selected the right channel and the subscriber has heard and selected the right channel, and he is in range of the base station and the base station receives a strong enough carrier with a strong enough tone on it, a signal is sent back to the operators position, to light the "CALL - LAMP" near the answering jack for the selected base station.
she then plugs into the traffic channel "answering jack", her voice is transmitted to the subscriber, confirms it is the correct subscriber and connects him to person who called him.
At the end of the call, the subscriber hangs up the handset, which switches the transmitter off and returns the receiver to the calling channel to await another "selective calling"
The radiophone operator notices the "Channel engaged" lamp going out ???
and unplugs from the traffic channel answering jack.
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Making a call
The subscriber will select one of the 3 traffic channels allocated for the area they are currently in.
Then they need to press the call button
The radiophone will then transmit a 2060 Hz tone on the traffic channel , and continue to do so for between 5 and 12 seconds after the "Call" button is released.
If the base station receives a strong enough carrier with a strong enough tone on it, a signal is sent back to the operators position, to light the "CALL - LAMP" near the answering jack for the selected base station at the Tate Gallery Telephone exchange.
The operator will then plug into the traffic channel "answering jack", her voice is transmitted to the subscriber, She asks for the radiophone users number, then connects him to the party he requires.
He can hear the call being set up ??
end of call ??