At 05:22 PM 6/4/05, you 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.
>
>Steve WA6ZFT
Years ago a group here in L.A. did the R&D and actually
breadboarded the hardware and had a couple of exciters
running.
The impetus was finding 25 Panasonic color TVs that ran
on +12v (made for RVs) in the city dump that has smashed
picture tubes.
They added a PLL to determine if the TV's color burst
oscillator was locked to the off-the air signal. This lock
signal was used to select F1 vs F2 on the exciter. F1 had
a regular channel element, F2 had the output of the
synthesizer. The synthesizer was designed around using
the TV color burst crystal as it's reference oscillator, and
output a sine wave signal into a channel element that was
modified to be a simple signal buffer (hint: the hole in the
element cover fits one manufacturer's SMA connector just
fine).
The system never got built - the group was getting free
rent at six prime privately owned sites (in exchange for
site management and maintenance duties) and the owner
sold out while the selling was good, and the sites went
from zero to $250 a month.
I have no info on the hardware design, the engineer that was
doing the work died from emphysema a while back.... his
smoking caught up with him.
Mike WA6ILQ
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