Its difficult to say unless you can contact an ex Tait dealer who maintained
a Local authority or Utility scheme. A similar unit by Pye/Philips I have
knowledge of, was the HS400. This contained a Toyocom 5MHz OCXO which was
used to lock a crystal producing the required excitation for the (analogue)
transmitter. There were two reasons for the offset, one was to avoid static
nulls were two overlapping areas had out of phase signals, and the offset
needed to be more than 20Hz (avoids flutter effects from the beats)and less
than 50Hz to avoid confusing the CTCSS decoders (tone squelch).
However later Tait gear in the 800 series was synthersized, I believe, so
this may be an stable reference source (OCXO or Rb) which could be daisy
chained to all the channel transmitters in the site. Rubidium is not
strictly necessary but was being installed in the 90s in some Police
systems. In fact the Rapco GPSDOs available on eBay some couple of years ago
came out, I believe, of London's Met Police system when they went digital.
Alan
G3NYK
----- Original Message -----
From: "Adrian Godwin" <artgod...@gmail.com>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Monday, January 11, 2016 1:11 PM
Subject: Re: [time-nuts] Tait reference
Yes, i found that description and it put me off buying one. But there are
also references on the web (including time-nuts archive) to surplus T801s
with rubidium sources.
Anyway, I took a punt and bought one.
So I'll find out soon :).
On Mon, Jan 11, 2016 at 11:18 AM, Charles Steinmetz
<csteinm...@yandex.com>
wrote:
Adrian wrote:
Are these the references with a rubidium oscillator ? They seem to have
similar models with OCXOs etc.
Tait is a manufacturer of mobile communications gear in New Zealand. The
T801 was part of a discontinued "quasi-synchronous communications system"
-- a form of simulcasting on the same frequency by transmitters at
different locations, to fill in dead spots. Tait's application was
utility
and public service mobile radios (not radio broadcasting, where this
scheme
has also been used). Here is Tait's basic description:
The Tait Quasi-Synchronous Communication System works by broadcasting
simultaneously from several transmitters on the same frequency. The
transmitters then operate as a single transmitter giving superior
coverage.
A Tait T801 Frequency Referenct Module acurately maintains the frequency
of the transmitters at each site.
Where required, the T801 allows small frequency offsets to prevent the
occurrence of static nulls in the overlap area.
The T801 module may be driven from one of a number of frequency
references, such as:
-- Rubidium frequency standard
-- Broadcast frequency standard
-- Oven Controlled Crystal Oscillators (OCXOs)
-- GPS Caesium Clock
This suggests that the T801 does not have an internal frequency
reference,
but rather requires a precision external reference to function. (It has
a
jack labeled "INTERNAL STD OUTPUT," but that may simply be a reference
that
is derived from the external standard, or a backup crystal oscillator to
keep the transmitter more or less on frequency if the external reference
signal is lost.)
Best regards,
Charles
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
