Steve,
I'm experimenting with that concept on VHF, duplicating an identical
installation
in my county's public-safety UHF system. Although I am using the Kenwood
TKR-740
repeater, the county system uses Kenwood TKR-840 and Motorola MTR2000 repeaters
with Hewlett-Packard/Symmetricom GPS-disciplined oscillators that provide
phase-synchronous 10 MHz reference inputs to the repeaters. Both of these
repeaters come standard with 5 or 10 MHz reference inputs. Once you have
multiple transmitters constrained to 0.01 Hz of their assigned frequency, you
need only account for differences in audio phase and delay. Of course, this is
much easier said than done, but the ready availability of GPS frequency
standards
on the surplus market makes the application achievable for Hams. Even so, a
simulcast system is not a cakewalk to design, and the system can crash
profoundly
if one of the transmitters loses its GPS synchronism, so multiply-redundant
components are advised.
73, Eric Lemmon WB6FLY
Steve Rodgers wrote:
> Has anyone implemented a simulcast (multiple TX's on the same channel) system
> for a ham 440 repeater system? It looks like you have to have TXCO's capable
> of
> tracking within a few hertz of each other.
>
> You can't do this with standard TCXO's, so I'm wondering if anyone has tried
> modifying a TCXO to lock to a GPS source, or NTP source.
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