Discussion:
SRS PRS10 RFC
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Luiz Alberto Saba
2018-12-03 16:59:31 UTC
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Hi people

I'm new on this list and miles below you.

I'm thinking of use a PRS10 with a LEA-6T providing 1PPS and a Raspberry
PI 3b+ with Lady Heather (2 instances, of course) to monitor/control
both devices.

Reasons for my request for your comments:

1. Power supply. 24 V switched is OK or the classic
transformer/bridge/huge capacitors/regulator is best?

2. Heat. Do I leave PRS10 "as it is" or should i use heat dissipator/fan?

3. LEA-6T or LEA-5T or one of these GPSDOs: Trimble Thunderbolt; Trimble
UCCM; Symmetricom UCCM; Oscilloquartz Star 4+; TruePosition gpsdo as the
source of the 1PPS?

4. Does anyone here have LH 6 source code? LH 5 does not talk with PRS10
(and with TruePosition too).

5. Just connect the 1PPS to PRS10 1PPS input or do I have to alter
something on the configuration?

That's it.

Thanks for your comments


Luiz Alberto Saba

a recently nut from Brazil


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Poul-Henning Kamp
2018-12-03 22:34:18 UTC
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--------
Post by Luiz Alberto Saba
1. Power supply. 24 V switched is OK or the classic
transformer/bridge/huge capacitors/regulator is best?
A good switched PSU is better than a mediocre linear PSU these days.
Post by Luiz Alberto Saba
2. Heat. Do I leave PRS10 "as it is" or should i use heat dissipator/fan?
Cool it, otherwise it dies too soon.

A stable temperature gives better performance.
Post by Luiz Alberto Saba
5. Just connect the 1PPS to PRS10 1PPS input or do I have to alter
something on the configuration?
The PRS10 1PPS input + PLL is tricky if you want to optimize
performance, because it is not really built for that.

If you feed a GPS 1PPS directly, the "hanging bridges" causes
the PRS10 to wander.

Running the GPS through an OCXO to get (mostly) rid of the hanging
bridges and then feeding a 1PPS derived from that, is likely too
good a signal for the mediore timestamping hardware in the PRS10,
which suffers from missing codes and unlinearity.

The best solution is to feed a GPS signal directly AND feed the
"negative sawtooth correction" via the serial port.

That way the jitter on the GPS signal dithers the mediocre 1PPS
timestamping, but the serial correction prevents the "hanging
bridges" from causing wander.

Not all PRS10 firmwares support this btw.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
***@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Dana Whitlow
2018-12-03 22:58:25 UTC
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Luiz,

I can express an opinion about the fan question. I think it is a much
better idea to use a thermally-massive heat sink, still with enough
fins to dissipate the heat. With a light (or no) heat sink the unit will
be much more responsive to local air temperature variations, meaning
that the frequency of the controlled oscillator will be less-well stabilized
by the feedback mechanism.

IIRC, you need to explicitly turn on the sync-to-PPS, although it's not
clear to me that there is any harm in leaving it on even when letting
the Rb run on its own.

At my previous job we had a PRS10 sitting on the shelf unused, and
I fired it up to see if it still worked (it did). But it used a switching
P.S.
for the heavy-draw stuff (oven etc), and a linear supply for the main
electronics stuff. I don't remember noticing any problems from that
arrangement.

Dana
Post by Luiz Alberto Saba
Hi people
I'm new on this list and miles below you.
I'm thinking of use a PRS10 with a LEA-6T providing 1PPS and a Raspberry
PI 3b+ with Lady Heather (2 instances, of course) to monitor/control
both devices.
1. Power supply. 24 V switched is OK or the classic
transformer/bridge/huge capacitors/regulator is best?
2. Heat. Do I leave PRS10 "as it is" or should i use heat dissipator/fan?
3. LEA-6T or LEA-5T or one of these GPSDOs: Trimble Thunderbolt; Trimble
UCCM; Symmetricom UCCM; Oscilloquartz Star 4+; TruePosition gpsdo as the
source of the 1PPS?
4. Does anyone here have LH 6 source code? LH 5 does not talk with PRS10
(and with TruePosition too).
5. Just connect the 1PPS to PRS10 1PPS input or do I have to alter
something on the configuration?
That's it.
Thanks for your comments
Luiz Alberto Saba
a recently nut from Brazil
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