GB3ZZ BRISTOL'S 1.3Ghz Amateur TV Repeater

The current logic control systemThe repeater has undergone some quite considerable improvements from its very earliest days back in 1984 when it was first switched on. The system back then used a relatively simple logic system based on the design used at "GB3US" voice repeater and printed in Radcom magazine January 1980 edition.

This controlled the TX, RX and test card generator circuits. In 1986 a new logic system was introduced it being jointly designed by Steve G8KUW and Brian GW6BWX and it is in fact this system that is still in use today, having undergone numerous hardware and software modifications. It has proved to be very reliable, although the BBC Micro is starting to get a little old now. The system has a total of forty updateable Teletext style pages, this is not genuine teletext as used by the commercial broadcasters but is rather the BBC Microcomputers mode 7 screens.

The text pages on GB3ZZ can be updated over the 6MHz audio sub-carrier using a spare BBC "B" Micro and a simple Teletext screen design program. The repeater also has several fixed pages that are held in an EPROM. These are used for things like contact and general system information that does not change very often, if at all. In more recent years Ian G6TVJ the group's "Cheif Engineer" has made considerable improvements to various parts of the system, with a particular emphasis put on the video processing circuitry employed.