[time-nuts] FTS4060 Continuing Saga

[Brooke Clarke]

Hi Tom:

It very well may be a wet connector (but they all are filled with Lube 
Gel silicon grease).
Yes the DC coupled setting was lost when the SR620 browned out, but the 
trigger levels are set by knobs and are not lost.
For a day or two after the brown out all appeared to be working fine.

The Time Interval numbers are all over the place, but consistent with 
the jitter (sigma) value.
If the integration time is shortened to say 10 seconds then there will 
be a number of averages that have a jitter of about 9 ns, but when the 
number of averages is raised to 100 the jitter is in the hundreds.

When the power cord is pulled for 10 seconds on the SR620 it seems to 
remember it's settings except the clock source changes to int from rear.

It also may be that that the receiver looses lock on all sats and is 
free running.  But this may be because at the time of my last posting I 
increased the elevation mask to 70 degrees, which may be too high.  Just 
now changed it back to 50 degrees which is where it's been for the last 
year or so.
At 70 degrees there were no sats.  I can't use time raim and the high 
elevation angle at the same time since it takes redundant sats for raim 
to work and a low elevation mask causes high jitter, making raim worthless.

But after changing to 50 deg El mask and locking to sat PRNs 1 and 25 
(with Eb/No in the 25 range) the jitter is still in the three hundreds.

Have Fun,

Brooke

Tom Van Baak wrote:

>Brooke,
>
>Check for a wet connector or cable at the GPS
>antenna.
>
>Check your SR620 settings. They are lost when
>you power cycle, yes? The jitter sounds more like
>an input trigger issue than GPS signal & rain issue.
>
>We get rain here all the time... It certainly doesn't
>cause the magnitude of what you're seeing.
>
>Did just the jitter change, or are you seeing a new
>phase offset and/or a new frequency offset than
>before?
>
>Did you have to re-load the zero-D coords into your
>GPS receiver? Make a lat/lon typo perhaps?
>
>/tvb
>
>----- Original Message -----
>From: "Brooke Clarke" <brooke at pacific.net>
>To: "Discussion of precise time and frequency measurement"
><time-nuts at febo.com>
>Sent: Sunday, March 05, 2006 12:02
>Subject: [time-nuts] FTS4060 Continuing Saga
>
>
>  
>
>>Hi:
>>
>>After Tom helped me a month ago to get the trigger level correct for 50
>>    
>>
>Ohm loaded TTL (1.25 volts), I've been seeing no aging on the FTS4060 s/n
>1013 and have been tweaking the C field and all was going well, but today
>(heavy rain) the jitter on each 500 second average has jumped up from about
>9 ns to more like 300 ns which means you can not believe the readings.  It's
>snowing on the nearby mountains and heavy rain here.
>  
>
>>Note that on prior days the daily spread in the Time Interval has been
>>    
>>
>around 10 ns peak to peak.
>  
>
>>So does GPS suffer with heavy rain?
>>
>>I checked TAC32 and the receiver settings are correct.
>>
>>Interesting sidelight:
>>A couple of days ago there was a brown out the caused the SR620 counter
>>    
>>
>and the computer to reset, but the FTS4060/S24 (no backup battery) did not
>reset (Lock and AC ON green LEDs) and the data shows that there was a
>recovery that lasted about 1,500 seconds.  Not sure what was moving.
>  
>
>>Have Fun,
>>
>>Brooke Clake
>>    
>>
>
>
>
>
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>  
>

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