Introduction



Being the Microwave interface to the satellites in space as the main reason for Goonhilly’s existence, it was important to display this form of technology as a central feature to the rest of the educational Communications Technology Workbench demonstrations. At the outset of Goonhilly in 1962, C-band waveguide was being used for long-distance Microwave land link communications, so it was inevitable that the first satellite links were made using the already available components. Receive paths were in the frequency range of 3.7-4.2GHz, and transmit paths were 5.8-6.3GHz. As technology developed, and more services needed more bandwidth, British Telecom, the Marconi Company, & the Department of Industry & Environment jointly had a new antenna (Goonhilly 4) constructed to explore the likely problems of using higher frequencies for satellite communications in the Ku-band (frequency range ~11-14GHz). It was also used to test the possibility for additional capacity doubling by orthogonally plane polarising channels (Cross Polar) of the same frequency and the degree of degradation which might be caused by rain showers. As the Heritage Society got under way, and the news percolated out that we were going to make simulations of as many aspects of the technology which was used on the Goonhilly site as we could, we were told that a range of receive C-band waveguide and equipment were to be recovered from the old West Wing by Goonhilly Earth Station Ltd., and could be made available to us.



Recovered C-Band Waveguide Components



C-Band Assembly Begins



Smaller Ku-Band Components Also Acquired



Evaluating Ku-Band Possibilities



Installation Construction



Whilst the waveguide was being assembled, plans for a wooden arch frame were drawn up to support the waveguide loops over the workbench. Frames were made up, installed on the worktop of a mobile bench unit, and painted in light straw colour to symbolise the standard for British Telecom’s equipment area rack-work.



Workbench Physical Dimensions



Proposed Frame Organisation



Bob's Completed Side Frames



Bob Painting Installed Frame



Assembling The Waveguide



The large size of the receive C-band components would make a quite impressive-looking part of the new Workbench so after a review of components available plus some additional recovered pieces donated from remaining BT store areas, the idea of the final configuration formed. Assembly began and a working “arch” completed, and in the meantime, removal of a small Ku-band Antenna (Goonhilly 8) made Ku-band parts also available, so we were able to create a second waveguide arch for this band as well. Both arches have integral waveguide switches, to either pass signals straight through each path, or they can be routed back down to the Workbench top to pass through other equipment to be on test if so desired. To distinguish the different frequencies, the C-band was kept black representing a receive path, whilst, where possible, the Ku-band was painted red in the colour of a transmit path. Some special proprietary components were left in the manufacturer’s original colour of dark green.


Final installation of each path was completed and made ready for testing, and the frequency bands checked with a repaired sweep oscillator together with a loaned Spectrum Analyser from one of our members.



Colour Matching Ku-Band Parts



C-Band & Ku-Band Installation



Attaching End Transitions



Des Setting Up Ku-Band Test



Testing Both Waveguides



C-Band Swept Frequency Response



Final Workbench Configuration



Although the Workbench is not yet fully completed, we now have acquired and are testing ancillary equipment to be installed in the small housings beneath the bench-top to create frequency up- and down-conversion of signals through the waveguides in much the same way as it did throughout Goonhilly's 45 years of satellite services for GPO/BT. This allows for a choice of intermediate frequencies (IF's) of 70MHz or 140MHz for interfacing to other proposed Workbenches which will be constructed in future. It is the aim that Audio, Television and Data signals will be passed over the simulated satellite paths as demonstrations.