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Simulcast Experiments

26 December, 2015 - Reading time: 2 minutes

Further to my earlier post on the use of a 10MHz reference in the KL, I've converted two KL70 exciters to 6m and fed them the same audio with both exciters locked to a common reference. If the reference frequency drifted, so did both of the exciters equally.

Each exciter was connected to an antenna (a 1/2 wave flowerpot, and a 2m 5/8 whip on a mag base on my shed roof). The mag base antenna was a obvious disadvantage to the system, so the power fed to the 1/2 wave vertical was reduced. I ran the full 200mW into the mag base antenna, and turned the exciters level down as far it would go for the 1/2 wave (around 40mW) which represented a power difference of 7dB. I did this in hope that I could make one transmitter worse than the other and notice the difference on air.

Well I forgot how well 6m propagates. Even with such low power and inefficient antennas with no gain, I travelled over 8km away behind several hills and bad terrain locally until the signal was lost completely. I could not tell any difference on air between the two listening to a broadcast. This was promising. Next test will be trying the transmitters at different locations and slightly delayed audio due to radio link distance delay.

This system could even possibly be implemented locally at the one repeater site. Another full repeater could be constructed on the same frequency, locked to the same reference and using a different antenna system, such as a horizontal antenna to cut down on mobile fade and flutter, or a yagi to fill a particular coverage gap. Then a two channel on site voter could vote which local receiver to use.