[time-nuts] Sub mm measurements with gps timing antennas?
SAIDJACK at aol.com
SAIDJACK at aol.com
Wed Apr 25 19:02:45 UTC 2012
Just brainstorming here, but how about this un-conventional approach:
Use a CSAC as a precise frequency reference for the LEA-6T. CSAC should
operate at <0.12W, I know, that's a lot, but maybe just worth a try.
To make the CSAC work, multiply the 10MHz up to the 26MHz the LEA uses.
Then place a small antenna loop around the LEA part to injection-lock the
internal 26MHz TCXO to the external antenna. That may work, or not.
Or unsolder the LEA-6T metal shield, and remove the TCXO, and replace it
with the externally generated stable 26MHz, then re-solder the shield. That's
cheaper than buying 2000pcs reels from uBlox.
It would be interesting to see how much more accurate the unit would become
with a stable 26MHz rather than a low-cost 26MHz TCXO.
AND: you can use the 1PPS output of the LEA-6T to actually discipline the
CSAC to GPS :)
bye,
Said
In a message dated 4/25/2012 11:42:52 Pacific Daylight Time,
attila at kinali.ch writes:
The problem with most of those techniques is, that they are not available
for the price the customer can afford. A dual frequency receiver costs
a lot more than an of the shelf LEA6-T. Also these modules are usually
build with larger power budgets in mind, e.g. the Trimble BD920 uses
1.3W typical, while the 0.3W max(!) of the LEA6-T already hurt us a lot.
Using an external frequency reference is not possible with the LEA6-T.
It would be possible to do that when using one of the GPS chipsets from
u-blox, but therefor we would need to take at least a full reel (iirc 2000
pieces), which isnt exactly cost efficient. Beside, we would still need
to use a TCXO, because there is not enough power available for an OCXO
or even an MCXO.
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