Note 1. Video and Multi-channel Telephony Radio Links 1956 - 1976, including products originally designed by GPO and Raytheon Inc.
Note 2. The product chronology is approximate and the research on-going
An upper-6GHz microwave link designed by the GPO Research Labs at Dollis Hill, which was developed for production and manufactured for the GPO by Pye Telecom.
After the war-time experience with the transportable microwave link equipment, Wireless Set No. 10, the Pye Ltd design team had concentrated on the design of commercial VHF PMR equipment and the RAF Instrument Landing System (ILS) which was a follow-on development from BABS.
In the 1950s the Pye group Chairman C.O. Stanley was a supporter of an independent commercial television service for the UK and recognised the need for additional broadband radio links around the country, to carry the video and audio signals from the studios to the regional transmitting sites. The General Post Office had monopoly control of radio links and he wanted to get into the business of supply to them, however the companies GEC and STC had a strong hold on the supply of link equipment to the GPO in the 2GHz and 4GHz frequency bands. Involvement with this 6GHz and 7GHz equipment gave Pye an introduction to the techniques needed for microwave communication and enabled them to build a small team to develop link equipment in this other frequency band where there was less competition.
A 6-7GHz microwave link equipment designed by Raytheon Inc. USA and manufactured under licence by Pye Telecom.
Three versions were available. A portable equipment with detachable aerials, a fixed rack-mounted version for permanent installations and a hybrid version with portable RF heads and the control equipment mounted in a 19 inch rack.
The equipment was suitable for carrying 405, 525 or 625 line television signals plus one sound channel. The transmitter RF output was 1 Watt from a tuneable klystron.
The M1000 fixed terminal equipment was, like the M1000A portable above, based on an OEM design by Raytheon Inc, USA. The equipment was re-designed to fit into a UK standard 19 inch rack, with the SHF waveguide components bolted into the top section of the cabinet and the 70 MHz IF, modulator, demodulator, base-band, metering circuits and power supplies below. The M1000 equipment was supplied to ITV companies for the UK television network, major industrial companies and the Ministry of Defence.
An example application of the M1000 was the London to Birmingham two-channel television link (main and standby) for ATV in 1960. The routing for this link was Highgate London, Barkway, Cold Ashby, Meriden, Birmingham.
An interesting feature of the link was the use of passive reflectors on the 200 foot high Pye Barkway mast and the microwave parabolic dish antennas mounted on the ground.
See the supervisory and monitoring control panel for this link at upper right, and a view of the ground-mounted dish and passive reflector on the Barkway mast at lower right.
The first own-design microwave equipment by the Pye Telecom Microwave Laboratory. The 19 inch rack based design had the SHF waveguide components bolted to the inside top rear of the rack and the TX modulator, RX 70 MHz IF, demodulator and base-band circuits were laid out on individual 3 inch high rack panels. The power supplies were plug-in modules at the bottom of the rack.
Three versions of the design were available. Type M710TV was suitable for carrying one television video signal to 405, 525 or 625 line TV standards along with its associated sound channel. Equipment type M710MUS would carry up to 6 high quality music channels, and Type M710 was suitable for carrying up to 960 telephone channels. The transmitter RF output was 1 Watt from a Klystron valve in the 5925-7800 MHz frequency band. A transistorised supervisory and monitoring panel provided a continuity pilot signal, monitoring of TX output power and automatic change-over in duplicated systems.
This equipment was supplied to a number of different countries and in the UK, to television networks and large industrial companies such as The Molins Machine Company and British Leyland Motor Holdings for video, telephone and data communications between their various UK sites.
A transportable version of the M710 fixed link equipment mounted in fibre-glass cabinets, produced for the British Post Office.
A 24 channel 1500MHz low capacity telephony or data link and the first all-solid state Pye microwave design.
The MC1500 link equipment was designed to operate between 1450 and 1535 MHz and conformed to the CCIR/CCIT recommendations for the time. The transmitter power output was 2 Watts making the equipment suitable for single or multi-hop operation of about 30 miles per hop.
The design was modular, with all of the radio units constructed in small flat aluminium cast modules, which were attached to a 3 inch high horizontal rack shelf by quick release Dzus fasteners, cableforms and plugs & sockets. The were mounted on vertical hinged PCB for rapid fault-finding or replacement. An engineers order wire circuit for speech communication over the link during test and alignment was provided as standard.
The launch customer was Eastern Electricity for use on the Whipsnade-Oxford, Whipsnade-Sandy, Sundon-Kensworth routes etc.
Photo of individual RF module to follow
The first Pye Telecom designed all-solid state high-capacity trunk microwave link, designed to carry 1 video signal plus sound channel, or 960 telephone channels. It operated in the upper 6 GHz frequency band.
The all solid-state RF output was 300 mW and for higher power outputs a travelling-wave tube amplifier was fitted which gave 5 or 10 Watts output. Part of the supervisory and monitoring system designed for the M710 was also utilised.
Although the equipment design was intended for 960 channel telephony, due to the limitations of the discriminator circuit used in the receiver 70 MHz demodulator, the equipment struggled to obtain adequate IF bandwidth, linearity and group delay distortion, and so was better suited to 300 channel telephony applications.
Photo of individual RF module to follow
A high capacity solid-state upper 6 and 7 GHz microwave link which was based on an NV Philips design and re-engineered to fit the ISEP rack shelf equipment used by Pye Telecom.
Operating in the frequency band 5800-7800 GHz the equipment was suitable for carrying a colour TV signal with sound channel or 960 telephone channels to CCIR/CCIT recommendations with good quality performance. Non-demodulating repeater versions were available which enabled long multi-hop networks to be constructed with minimum video performance degradation. A new design 6+2 supervisory and monitoring system was available, as with the M1117 equipment below.
The type M717 was available with 5, 10 or 20 Watt RF output travelling-wave tube amplifiers in the transmitter. Type M718 provided a solid-state RF output power of 300mW without the use of a travelling-wave tube.
The launch customer for this equipment was the British Post Office, to expand the television transmission capacity of the London to Birmingham microwave route.
The image to the left shows a three-hop duplicated M717 system with two transmitters and two receivers per hop.
The Pye M1117 11 GHz broadband microwave link equipment was a logical development from the 7 GHz M717/M718 equipment. While the microwave transmitter and receiver assemblies were all new designs, the same 70 MHz modulator and high-level IF amplifier was used in the TX. In the receiver the same pre-IF amplifier, main IF amplifier, demodulator, group delay equaliser and baseband amplifiers were used from the lower frequency equipment.
The photograph at left shows the Laboratory test and development system at Gloucester Street, Cambridge in 1970. This system was equipped with two complete transmitters and receivers plus the 70MHz IF switches and supervisory logic to control a 6+2 channel multi-hop system (6 working microwave RF channels and 2 standby channels).
Counting from the left, the first two racks contain the 11GHz transmitter and receiver SHF shelves (vertical sliding assemblies terminated with flexible waveguide), two travelling-wave tube amplifier power supplies and all the modules listed above which operate at the 70 MHz IF frequency. The third rack contains the pilot tone oscillators & receivers and link monitoring supervisory logic equipment. The fourth rack contains the 70 MHz IF switches and control logic, and the fifth rack contains the baseband amplifiers and input/output baseband (video or telephony) distribution connections (as far as I can remember!). The whole system was powered from a bank of float-charged 48Volt batteries fed from a huge power supply in a separate battery room.
At right is a close-up of the 11GHz transmitter shelf showing the WG17 waveguide components and the high-level IF amplifier PCB (70MHz IF driver to the transmit mixer).
A version of the M717/M718 with narrower waveguide filters to allow the use of twice the usual number RF channels in a given spectrum. This equipment was also used for carrying defence related radar traffic, which needed a wider IF passband and very sharp skirt waveguide filters to obtain the required selectivity.
The replacement for the MC1500 low capacity link. L300 was a modular equipment and available in a wide range of frequency bands.
The photograph at right shows the equipment set up in the Microwave Lab for the publicity image used in the product brochure.
A version of the M717/M718 equipment mounted in short 4 foot cabinets for the British Post Office for use as temporary microwave link stations.
This was the last Pye broadband link equipment design to be manufactured.
By 1976 the political in-fighting between the dedicated PMR radio side of the Company and the ‘Other Activities’ (microwave links, telemetry, digital telephone exchanges etc.) resulted in the Microwave Lab being closed. The writing had been on the wall for the Microwave Lab for some time after a former leader of the Mobile Lab became Technical Director.
After a long type-approval testing program the M717/M718 equipment design had finally become approved for use in the main Post Office trunk microwave network and was working well in the field. Earlier in 1976 the Post Office had wanted Pye to supply the M717/M718 equipment to extend the capacity on the Manchester to Carlisle microwave route. Although this was a competitive tender situation, in complete confidence, necessary facilities were granted to allow Pye engineers to measure the RF characteristics of the waveguide installations in the individual microwave stations along the route to enable the Pye waveguide filters to be interfaced with existing equipment. However, when the tenders were submitted the Company management instructed the Broadband Systems Planning group to set a particularly high price, and despite being given the opportunity to revise the tender figures the Company declined. From that point Pye Telecom walked away from the high capacity microwave business and closed down the Microwave Laboratory. The Post Office was so enthusiastic about this equipment that they even purchased all the lab prototype material for spares when the Lab finally closed down.
After the Microwave Lab closed down, the floor space at Gloucester Street, Cambridge was used for system testing the M723 GPO transportable racks, and was later taken over by Mobile Lab 4.
Design responsibility for the MC1500 and L300 low capacity links was passed to the Fixed Station Laboratory, designers of the L700 link equipment which will be summarised below.