[time-nuts] Tait reference
stephen at tompsett.net
Mon Jan 11 14:12:40 UTC 2016
The T801 units I have seen in the UK contained a rubidium 10MHz reference
(FRS form factor) and a synthesizer that could produce several outputs of a
nominal 12,8MHz, but which could be individually offset slightly to allow
for precise offsetting of the transmitter frequencies by a few Hz for use
in a quasi-synch PMR system.
On 11 January 2016 at 11:18, Charles Steinmetz <csteinmetz at yandex.com>
> 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.)
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