Same Frequency

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Farnsworth Peak Utah

Fransworth Peak (29 km) south west of Salt Lake City, Utah
One of the repeaters on the same frequency as another nearby repeater.
(what a great photograph)

WARG had an opportunity to find out what happens when you place two repeaters, that are in similar locations, on the same frequency. A 2 metre repeater at Roleystone and a 2 metre repeater at Lesmurdie, were set up to operate on the same input - output frequencies.

The repeater locations are 8 kilometres apart and are at the same height, so the coverage from both repeaters is about the same.

The reason for the test was to find out if two repeaters one the same frequency in the same area would improve coverage. Where one repeater had poor coverage perhaps the other repeater would have better coverage, particularly for mobile stations who experience flutter in any given locations.

Some outcomes were known. Firstly the two repeaters had to be on the exact same frequency, otherwise the frequency difference between the two would result in an varying in level audio tone equal to the radio frequency difference. Also the audio phase of the two repeaters had to be the same, otherwise that audios would tend to cancel each other out.

The frequencies of the two repeaters could be adjusted to within a few Hertz. Yes they would drift, but one repeater was located at my QTH in Lesmurdie, and could be adjusted from time to time to match the Roleystone repeater.
Switch on
The two repeaters were switched on and the results came in.

Firstly the amount of unwanted interaction between the repeaters was much less than thought. There was no audible tone due to the close matching of frequencies, and normal mobile contacts were made. However, what was quickly noticed, was the audio varied in level and even at times almost fading away.

One issue with the trial, was the coverage better than a single repeater? This proved difficult to come to a conclusion. The trail only ran for a few days and results were in determinant. Also to licence such a system back then would not have been possible, so after a few days the system was returned to separate frequency operation.
The Internet
The Internet really is a magnificent research tool. I came across this link to a system in Utah that runs two repeaters in similar locations on the same frequency, that has some real results of such a system. Makes for most interesting reading.