[time-nuts] FTS125 GPS Module

Azelio Boriani azelio.boriani at screen.it
Thu Jun 28 19:20:27 UTC 2012


>other GPS receivers have the same exact problems when left in
 >holdover for hours or more

Are you sure? Never seen that behavior on a Trimble, Motorola/iLotus,
uBlox, Sanav or SkyTraq  receiver, only on NavSync.

The locking algorithm of the FTS250 (and maybe the FTS125 too) is a
National LMX series PLL chip (I can't remember the exact part number, have
to check with the FTS250 COO we have).

On Thu, Jun 28, 2012 at 8:25 PM, <SAIDJACK at aol.com> wrote:

> Hello Martyn,
>
> I evaluated the FTS125 TCXO module (FTS250 model) as well, and found  it to
> have massively more phase noise and spurs than its specification, and  to
> have a huge frequency jump of 1.2E-7 (1.2Hz) when coming out of just a
> couple of minutes of holdover.
>
> See the attached test results. I did not test the unit for very long
> holdover, but other GPS receivers have the same exact problems when left in
> holdover for hours or more, and a good GPSDO will address that issue in
> it's
> firmware so as to make it transparent to the user.
>
> Of course the FTS125 doesn't have firmware other than what is in its GPS
> receiver, as its locking algorithm is inside a PLD.
>
> bye,
> Said
>
>
> In a message dated 6/28/2012 07:45:23 Pacific Daylight Time,
> expertengineer at live.co.uk writes:
>
> Hello,
>
> Has anyone had a play with the FTS125 GPS reference  from Connor Winfield.
>
> I have one question on it.
>
> I notice if the  unit is locked to GPS and the antenna is removed, the unit
> goes to holdover  which is correct.
>
> If the antenna is replaced quickly (within minutes)  then the module
> changes back from holdover to GPS lock, which is what I would  expect.
>
> However, if the antenna is left out for hours, then  re-connected, the unit
> never goes back to GPS locked and remains in holdover,  this despite 8 or
> more satellites being received.
>
> I have tested  multiple boards and they all do this.  This is on the CTV
> TXCO  version.  I haven't tested the COO version yet.
>
> Anyone else seen  this.  Any fax?
>
> Best  Regards
>
> Martyn
>
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