Operators of the GB3ZZ amateur television repeater station
Well, the simplest description would be to say it's a TV receiver hooked up to a TV transmitter so whatever is being picked up gets re-broadcast again.

Of course, there's a bit more to it than that, for one thing, if the receiver picked up its own transmitter - and fed it's signal back to the transmitter, which was picked up by the receiver again - we would soon be in a circle of feedback. Incest on the air !

We get around that problem in two ways:

1. The receiver and transmitter are tuned to different frequencies (channels),
2. We put a special filter between the receiver and it's antenna to block signals on the transmitters frequency so the receiver doesn't see them.

Having got to the stage where we can send and receive simultaneously we need to decide when and what the transmitter should be sending. There's little point in receiving nothing and retransmitting it, all we  would achieve would be a picture of 'snow' against a snowy background.  We do something clever at this point, we look to see if anything is arriving at the receiver and if there is we pass it to the transmitter - but - if all the receiver is seeing is snow, we send something more useful instead, a test card.  That's why if you look at the live picture on the GB3ZZ page it shows colour bars most of the time, they are part of a series of test cards.

Why the test cards? - well they serve three purposes:

1. They identify the station, that's a legal requirement.
2. They provide a pattern which can be used to adjust any receivers looking at them.
3. They provide a steady signal that can be used to aim antennas for best reception.

Why do we need repeaters?

We don't NEED repeaters but they are very useful devices for a number of reasons:

1. They help to extend the range of a transmission by acting as a booster along the way.
2. They can provide a link over obstructions which otherwise would block the path.
3. They allow more people to participate at the same time.
So just what is an ATV Repeater then ?
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