Message-ID: <004301c09608$05ddca60$1b0d97d4@oemcomputer>
From: "Johan Bodin" <sm6lkm.jbeab@swipnet.se>
To: rsgb_lf_group@blacksheep.org
Subject: SV: LF: GPS-Disciplined BPSK
Date: Tue, 13 Feb 2001 22:57:55 +0100
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Hi

Bill VE2IQ wrote:

>I checked with Garmin on this and they're standing by their 1 microsecond
>spec.  They suggest using the GPS25-LVS (which apparently has a mode where
>you can specify that the location is fixed and let it concentrate on
>calculating the time accurately) - and say that under good signal conditions
>the 1PPS output will track UTC "well within" the 1 microsecond limit.
>They say typical accuracy is 100 nsec RMS with 50 nsec jitter.


Another alternative is Motorola Oncore UT+ which was designed specifically
for timing applications. It has a "Site Survey" function which, if started, calculates
the average of 10000 position measurements and then enters "position hold mode".
When in position hold mode, it delivers accurate time with as little as one satellite
in view. The 1PPS output is specified to be within 50ns of "true time" (GPS time
or UTC, selectable) with SA on. Now that SA is gone, the accuracy is even better
(there is always a ~30ns sawtooth error due to finite resolution in the software/hardware).

http://www.motorola.com/ies/GPS/products/produt.html

I am using an UT+ in my frequency standard - a modified version of Brooks Shera's
design - and I am very happy with it.

http://www.rt66.com/~shera/index_fs.htm

For LF use, the 10MHz output from the standard can be used for DDS clocking
(RX/TX LO) and the 1PPS output, or submultiples thereof, can be used as a bit clock.
The time message from the serial port can be used for message framing.

If you feel that 32-bit DDS resolution is inadequate, have a look at the ISL5314 DDS
chip from Intersil/Harris. It has a 48 bit phase accumulator and a 14-bit DAC on-chip...

73
Johan SM6LKM