We do not experience the deep null you are describing, but I remember SkyTel
doing exactly what you describe, that is, building in a slight error in
frequency, for their Flex Paging.
I used to think that using minimal transmitter power was a key to simulcast,
but this makes the non-capture area larger. The higher the ERP, the smaller
the non-capture area will be. We define a capture area as that where one of
the transmitters has a 10 db advantage. Most of the anomolies occur in the
non-capture areas where neither transmitter predominates.
In the system that I maintain we use GPS disciplined 10 Mhz. Oscillators
that are pretty much DEAD ON. In planning delays we want the audio from the
transmitters to arive at the same time in the overlap areas. I doesn't
matter in the captured areas very much.
Each transmitter site has 19 RF channels in the 856Mhz band and each site is
fed via a 1.544 mb/s T1 data stream. Audio delay is accomplished using bulk
delay in the entire T1 stream.
I wanted to try simulcast between Temple and Killeen 2M sites, but, in
addition to the frequency stability issue, we would need site voting, and
reliable RF links between the two sites. For me it is more trouble than it
is worth. I don't know about your ham clubs, but in a County of 250K, we
have only a handful of qualified technicians, and only a couple in our club.
I can see how this could easily go from being a hobby enterprise to being
WORK, of which I have plenty.
Best 73,
Steve NU5D
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