[time-nuts] Tait reference

Alan Melia alan.melia at btinternet.com
Mon Jan 11 10:29:54 EST 2016


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" <artgodwin at gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at 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 
> <csteinmetz at 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
>>
>>
>>
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