History

The television link to the Isle of Wight was an early microwave system which developed in stages from 1954 to 1959. According to Radio Times, Rowridge was "The first of the BBC's five medium-power television stations..." when it entered service in November 1954. Coverage extended from Dorset to West Sussex with Hampshire being the main service area. At this stage BBC main transmitters were fed via cable, where feasible. In some cases "direct-pick-up" was used - an existing transmitter was received off-air at a suitable intermediate site and forwarded. An article in the Post Office Electrical Engineers' Journal (POEEJ), April 1955, notes that this option had been used at Belfast (where the programme feed continued cable) and the Isle of Wight link was the first where a microwave link formed part of the arrangements. This was intended to be a temporary solution which "enabled the service to be established more rapidly..." and was referred to as "Stage 1".

The 1954 arrangement used a site at Golden Pot (near Alton) where a 325 ft mast allowed a two "hop" microwave link to be planned. It seems the location was fairly critical: if a site in that area had not been available it would have been necessary for two intermediate sites to be used. The Stage 1 microwave link operated only from Golden Pot to Rowridge - the London BBC transmitter (originally Alexandra Palace) was recieved with sufficent strength to be used as the source. The POEEJ article notes "it was not possible to carry out any microwave propoagation trials [...] but theory and previous experience indicated that the performance should be satisfactory". Other economies were made in the development of the route, for "The microwave equipment for the link has been recovered from the Dollis Hill - Castleton experimental link." It was overhauled and modified, however, with two channels operating continuously - the BBC would switch between the two as necessary. Golden Pot was intended to be unmanned. The frequencies 3.930 and 4.070 GHz were used as "Band-pass filters for those frequencies were available" - also recovered from an earlier temporary link. The two transmitters were combined and fed to a single dish at Golden Pot.

Meanwhile, down at Rowridge, further temporary arrangements were in place. The BBC started service using a 200 ft self-supporting tower - formerly used by the Post Office at St Albans. A dish was installed to allow reception of the link from Golden Pot. It may be no great surprise to learn "The station at Golden Pot comprises three B-1 type timber buildings..." - these were a standard design often used for rural telephone exchanges.

Stage 2 of the link essentially involved conversion of the off-air section to a microwave link between London (Museum Exchange) and Golden Pot and re-arrangement so the route could be used in the return direction for outside broadcasts. The "twin path" system continued, now requiring four channels in the 4 GHz band. Stage 2 was fully operational by 1956.

The start of ITV transmissions from Chillerton Down, also on the Isle of Wight, led to further revision. The studio was to be in Southampton with plans for a further transmitter at Dover. This required a vision circuit from London to Southampton to provide "Network" and least one link from Southampton to Chillerton Down, plus a much longer link from Southampton to Dover. "Stage 3" therefore provided a one-way link from London to Rowridge together with a cable link to Chillerton Down and a separate two-way microwave link to the central exchange in Southampton. Cables to and from the studio completed the arrangements and allowed broadcasting to commence. Post Office Research Report 20250 comments that Stage 3 provided the ITA link as a "twin path" arrangement - overall four channels at 4 GHz were used from London to Rowridge, but carrying only two vision circuits. This over-provision would be addressed in "Stage 4" when the system would change to a 2 + 1 arrangement with common "protection channel" in each direction. The additional return channel was connected to an existing trunk cable towards Dover, allowing the studio output from Southampton to be transmitted from Dover. Stage 4 was operational from July 1959 (however the Dover transmitter did not enter service until January 1960).

The equipment for Stage 4 had been recovered from the (temporary) London - Wenvoe link which itself had used equipment originally installed for experimental purposes. It seems some modifications had been made with the designations RS 10/5 given to the 1954 Stage 1 equipment and RS 10/7 applied to that installed in 1958. Some sources suggest Pye were involved in the manufacture of RS 10/5 although this was a Post Office design.

The conclusion to Report 20250 is "interesting"..."The equipment has proved reliable [...] but some fading of the signal has occurred. This is attributable to the rather long hops of 40 and 42 miles, coupled with [planning assumptions used in 1953 which had been revised due to experience]. The performance of the route will have influenced its replacement which used two intermediate sites between London and Southampton. The new scheme avoided "doubling back" and effectively treated Rowridge as an extension from Southampton. Due to delays in completion, however, a temporary arrangement was used from 1966 for BBC2.

The London - Golden Pot - Rowridge section of the link was built by the Post Office using equipment recoverd from previous schemes. In contrast the extension between Chillerton Down and Southampton was subject of contracts 21826 and 21864 ("additional channels") awarded to GEC in April 1958 and January 1959 respectively. The additional channels are likely to relate to "Stage 4". The Chillerton Down - Southampton section operated at 2 GHz with antennas installed on the ITA transmitter mast and on the roof of the Southampton exchange at Ogle Road.