: [time-nuts] Sneaky Errors
Playing with my A unit Timex (It takes a licking and keeps on ticking) I'm
not getting a reliable unlock even at + or - 5V
Once unlocked, it seems to need to be inside 1.2V before locking.
That results in about 4 hz error, which would be ok for me.
Is there a way
If you are very conservative or if this is for some critical requirement then
I'd get something other than another TB.
That's a good point.
There are 2 obvious single points of failure in using TBolts. One is TBolt
firmware (or obscure design error). The other is the GPS system.
If you
Yup, I agree.. If I could count on the Tbolt output going dead if there's a
problem, that would be wonderful, but my worst fear is that it would keep on
going but be wrong enough to matter. We are calibrating other equipment
against the TB output to 1ppm so the TB would have to be pretty far
1 ppm at 10 MHz is 10 Hz. It's been quite a while since I tested it, but if
I remember correctly, if the Tbolt OCXO is off that far the GPS won't lock and
the failure will be rather obvious.
The typical Tbolt oscillator has a DAC gain of 3.5 Hz/V. 10 Hz would be 3V of
DAC offset. Lady
I have two thunderbolts, set up so that I can switch over to the backup unit if
the primary fails.
All is well with that, but what could I do to detect a less obvious failure,
like 9.99 MHz output?
If they disagree, I don't know how to resolve which is correct.
The thunderbolts produce status information and error estimates about how
they are doing. If you are willing to trust that, you can remove the one
that is falling out of tolerance. If you aren't willing to trust that, then
I'm pretty sure you'll need a third frequency standard to compare each
I have two thunderbolts, set up so that I can switch over to the backup unit
if the primary fails. All is well with that, but what could I do to detect a
less obvious failure, like 9.99 MHz output?
If they disagree, I don't know how to resolve which is correct.
Get a 3rd. 2 good guys
that can be turned on or off to compare.
Joe
-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Hal Murray
Sent: Wednesday, October 19, 2011 3:03 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Sneaky
On Wed, Oct 19, 2011 at 12:46 PM, David VanHorn
d.vanh...@elec-solutions.com wrote:
I have two thunderbolts, set up so that I can switch over to the backup
unit if the primary fails.
All is well with that, but what could I do to detect a less obvious
failure, like 9.99 MHz output?
If
Simple way is to use LadyHeather.
From its output, you can tell if either or both are working correctly as
well as how well they are working.
That is assuming of course that there is at least one working GPS satellite
in view at all times.
If not it well tell you that also.
ws
This is the famous man who has two watches does not know what time it is
problem.
Lucent solved it for telecom with the RFTGm (Reference Frequency and Timing
Generator) equipment, consisting of GPS disciplined OXO and Rubidium
oscillator modules that continuously checked each other via 1 PPS and
Out of curiosity, what would be the consequences of a steadily increasing
phase error? Would it offend your sense of perfection or would it have real
consequences?
Phase error wouldn't bug me. My worst fear is that the 10.00 MHz standard
might be 10.02 MHz.
I need to implement
On 10/20/2011 12:18 AM, David VanHorn wrote:
Out of curiosity, what would be the consequences of a steadily increasing
phase error? Would it offend your sense of perfection or would it have real
consequences?
Phase error wouldn't bug me. My worst fear is that the 10.00 MHz standard
Steadily increasing phase error is to let there be a frequency error.
Frequency is the derivate of phase, so it comes with the territory.
So a 200 ns per second phase drift would provide a frequency error of 2
Hz on your 10 MHz. Can't have one without the other.
I understand, I'm just saying
On 10/20/2011 12:57 AM, David VanHorn wrote:
Steadily increasing phase error is to let there be a frequency error.
Frequency is the derivate of phase, so it comes with the territory.
So a 200 ns per second phase drift would provide a frequency error of 2
Hz on your 10 MHz. Can't have one
Seems to me that 200 ns is 720 degrees of phase error, which is a lot.
A person handy with logic circuits could build a simple phase detector
with a flip-flop and an RC filter with a tenth second time constant.
An analog circuit could detect 360 degree rollover and set off alarm
bells. Note that
I believe that the Thunderbolt firmware would catch such a thing.There is
quite a bit of error checking and TRAIM (time receiver autonomous integrity
monitoring) done.
If the osc was off in freq, the firmware would try to use the EFC voltage to
slew it back into agreement with the GPS
Maybe this is too simple
LadyHeather is always checking the Tbolt's Internal Osc value against the
GPS.
By watching it's plot outputs you can tell if the Tbolt is on freq.
(compared to the GPS)
If no plot outputs, then something is broken, at that point is does not
matter what, can assume it
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