[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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