Re: [time-nuts] Holdover: Z3801A vs KS-24361

[Bob kb8tq]

Hi

There isn’t much you can really see on a GPSDO comparing it to a normal OCXO. 
The OCXO simply is not accurate enough. You need something like a Cs standard,
a different GPSDO, or a good Rb for the reference. (Yes, if you have a hydrogen 
maser, you *can* use that ….). 

First thing to check is the DAC readings on the unit ….

Bob

> On Apr 15, 2018, at 6:59 AM, Hal Murray  wrote:
> 
> 
> kb...@n1k.org said:
>>> A  KS-24361 says:
>>> Predict  394.1 us/initial 24 hrs
>> That would suggest the unit is unlocked. It should be below 10 us. Just as
>> with the 3801, the estimate is a bit fuzzy. You should be able to see issues
>> in the data on the Z3809/Z3810. 
> 
> It says it is locked and has been locked for days.
>>> Locked to GPS  TFOM 3  FFOM 0
> 
> I used this as a learning exercise for my new TICC.  Something is clearly 
> fishy.
> 
> The reference for the TICC is the crystal in a HP 5334B with the good-crystal 
> option.  It's not calibrated, but there isn't any GPS logic to jerk it 
> around.  I assume the swing is due to temperature.  I corrected the slope of 
> the graph by hand.
> 
> Here is a day+ of data:
>  http://users.megapathdsl.net/~hmurray/time-nuts/TICC/TICC-KS.png
> 
> Here is a zoomed in chunk:
>  http://users.megapathdsl.net/~hmurray/time-nuts/TICC/TICC-KS-2.png
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 

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Re: [time-nuts] Holdover: Z3801A vs KS-24361

[Hal Murray]

kb...@n1k.org said:
>> A  KS-24361 says:
>>  Predict  394.1 us/initial 24 hrs
> That would suggest the unit is unlocked. It should be below 10 us. Just as
> with the 3801, the estimate is a bit fuzzy. You should be able to see issues
> in the data on the Z3809/Z3810. 

It says it is locked and has been locked for days.
  >> Locked to GPS  TFOM 3  FFOM 0

I used this as a learning exercise for my new TICC.  Something is clearly 
fishy.

The reference for the TICC is the crystal in a HP 5334B with the good-crystal 
option.  It's not calibrated, but there isn't any GPS logic to jerk it 
around.  I assume the swing is due to temperature.  I corrected the slope of 
the graph by hand.

Here is a day+ of data:
  http://users.megapathdsl.net/~hmurray/time-nuts/TICC/TICC-KS.png

Here is a zoomed in chunk:
  http://users.megapathdsl.net/~hmurray/time-nuts/TICC/TICC-KS-2.png


-- 
These are my opinions.  I hate spam.



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[time-nuts] Holdover: Z3801A vs KS-24361

[Mark Sims]

SS is signal strength.  CN is carrier to noise ratio.   They basically indicate 
the same thing, but their scale may be different.   You can't compare the 
absolute magnitude of the values from different types  of receivers,  only do 
relative comparisons.   Other receivers can report dBc, etc.  And Trimble 
devices can report AMU (amplitude measurement units).  Some Trimble devices 
don't support dBc readings.  By switching a Tbolt between AMU and dBc, I worked 
out a table that Lady Heather uses to convert AMU to dBc to that those devices 
can display the more common dBc values.  On the Trimble devices you set the 
signal level mask in AMUs.

---

> the Satellite Status area has a header of SS on the Z3801A and C/N on  the KS
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Re: [time-nuts] Holdover: Z3801A vs KS-24361

[Bob kb8tq]

Hi



> On Apr 12, 2018, at 1:30 AM, Hal Murray  wrote:
> 
> On that Status page, A Z3801A says:
>  Predict  2.5 us/initial 24 hrs

That sounds about right for a 3801. The prediction is something better than
a wild guess and not what one would call a solid number.


> 
> A  KS-24361 says:
>  Predict  394.1 us/initial 24 hrs

That would suggest the unit is unlocked. It should be below 10 us. Just as with
the 3801, the estimate is a bit fuzzy. You should be able to see issues in the 
data
on the Z3809/Z3810.

 A prediction of < 1 can pop up on occasion, on either unit. More typical 
estimates
are in the “couple of us” range. If you yank the antenna, it still does a 
respectable 
~5 us / 24 hrs or so either way. 

> 
> Both have been running for weeks.
> 
> Is anybody seeing similar?

no

> 
> 
> Also, the Satellite Status area has a header of SS on the Z3801A and C/N on 
> the KS.  Does anybody know the units and/or what that is actually measuring?

There are tables that translate the Motorola (and some of the other brands) 
status 
numbers into rough dbc/ Hz. I would not count on the numbers on a 20+ year old
design lining up directly with the latest and greatest modern module. 
Apparently 
the SNR calculations are a bit weird.

Bob

> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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[time-nuts] Holdover: Z3801A vs KS-24361

[Hal Murray]

On that Status page, A Z3801A says:
  Predict  2.5 us/initial 24 hrs

A  KS-24361 says:
  Predict  394.1 us/initial 24 hrs

Both have been running for weeks.

Is anybody seeing similar?


Also, the Satellite Status area has a header of SS on the Z3801A and C/N on 
the KS.  Does anybody know the units and/or what that is actually measuring?

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