(To the list this time!)

   "Almost every cellphone contains a TXCO"

This solution is trivial anymore since the
advent of the microprocessor (MEASURE the
ambient temperature, do a look-up in a table
BASED on that particular crystal's "curve"
(see Peter's postings) and feed a DC voltage
to a vari-cap diode incorporated in the
crystal oscillator's circuit!) - OR -

- anymore it's a real easy matter to 'slave' the
cell phone's frequency from transmissions coming
on the "downlink" side (from the base station).

Heck - the Ericsson RBS882 BS (base station) gear
was synchonized to the 1.544 MBit/Sec "T-span"
coming from the MTSO (mobile telephone switching
office) where all the 'clocking' on those spans
is derived from very accurate sources (a higher
tier point from somewhere else in the network)!

RF (and telco) Jim



----- Original Message -----
From: "Mike Harrison" <mike@WHITEWING.CO.UK>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, August 14, 2002 5:02 PM
Subject: Re: [OT]: What Test Gear to measure xtal frequency to 1Hz


On Wed, 14 Aug 2002 22:24:11 +0300, you wrote:

>On Wed, 14 Aug 2002, Mike Singer wrote:
>
>>Harold M Hallikainen wrote:
>>> Also, remember that setting a 12 MHz oscillator to
>>> within 1 Hz means it isn't going to stay there.
>>> That's 0.1 ppm. Really good crystal oscillators
>>> (with temperature compensation or ovens) can maybe
>>> do 1 ppm or so.
>>
>>Yes, from Electronicstalk.com:
>>
>>"The FTS501AH OCXO offers a frequency stability of
>>+/-250ppb over the standard temperature range of 0 to 70C"
>>
>>(ppb = 1000 ppm ?)
>
>Yes, billion = 1e9
>
>The only small problem is price. Fox TCXOs were around $40 when I last
>checked and the spec was worse than 0.25ppm.
Almost every cellphone contains a TXCO, therefore they must be
gettable for a lot less than $40.....

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