Simulcast Stories:
The largest Newspaper in the SF Bay Area has two high
level micor era repeaters set up exactly the same. Both
come up at the same time from two 30 mile distant
mountain tops with wireline and repeat control.
Both repeaters are standard channel element types
ie not high spec. They were both net with the same
service monitor after a 1/2 monitor warm up.
You'd be surprised how well the dual system works
and stays close enough to be kept in use. The large
number of mobiles drive in and out of capture zones
and the audio seems to always be usable.
It's not pretty or high spec, but it proves that
even a fudged system can work well enough for some
people.
If the transmitters are similar type, they both
tend to drift or track the same direction with
time and temp. When the repeaters get far enough
out of sync, they are simply re-net back to Fop.
Many times over a year has gone by without having
to re-net the tx channel elements. Weird, but the
silly system works pretty well.
cheers,
skipp
> "Steve S. Bosshard" <[EMAIL PROTECTED]> wrote:
> 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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