[time-nuts] FTS4060 Continuing Saga

Brooke Clarke brooke at pacific.net
Mon Mar 6 14:40:40 EST 2006


Hi Gar:

Interesting.  I just tried a 30 minute power down, and again the ALIGN 
light in on.  So I guess it's an overnight power down to get it reset.

More tomorrow,

Brooke

NE8S wrote:

>Brooke,
>
>Now that you mention it, I did power down at first for 45 minutes. After 
>this initial power-up sequence, the same prevailed. I then decided on the 24 
>hour down period for the oscillator and cesium ovens to fully recycle.
>
>Gar
>
>----- Original Message ----- 
>From: "Brooke Clarke" <brooke at pacific.net>
>To: "Discussion of precise time and frequency measurement" 
><time-nuts at febo.com>
>Sent: Monday, March 06, 2006 11:54 AM
>Subject: Re: [time-nuts] FTS4060 Continuing Saga
>
>
>  
>
>>Hi Gar:
>>
>>OK.  It's time to pull the plug and leave it out for awhile.
>>I tried pulling the plug for 10 seconds, but that may not have been long
>>enough to get the oven cooled down.
>>
>>More later,
>>
>>Brooke
>>
>>NE8S wrote:
>>
>>    
>>
>>>Brooke,
>>>
>>>One of my FTS4060's behaved the same way during a power interrupt. It was
>>>the only one that was not on a UPS. After many attempts to reset the logic
>>>while powered up, I finally brought the clock down and 24 hours later,
>>>powered it back up again. As a result, it performed its normal power-up
>>>sequence and the control logic seemed to have reset itself properly. It 
>>>this
>>>point, it was back to normal. It has been fine ever since.
>>>
>>>First time it has happened to me. I am mainly an HP man and very much 
>>>prefer
>>>the HP clocks and their digital logic structure and methods.
>>>
>>>Hope this helps a little.
>>>
>>>Kind regards,
>>>
>>>Gar  Ko
>>>NE8S
>>>CsUTC Observatory
>>>Bio-Nucleonics Laboratory
>>>
>>>----- Original Message ----- 
>>>From: "Brooke Clarke" <brooke at pacific.net>
>>>To: "Tom Van Baak" <tvb at leapsecond.com>; "Discussion of precise time and
>>>frequency measurement" <time-nuts at febo.com>
>>>Sent: Monday, March 06, 2006 10:58 AM
>>>Subject: Re: [time-nuts] FTS4060 Continuing Saga, GPS rain
>>>
>>>
>>>
>>>
>>>      
>>>
>>>>Hi Tom:
>>>>
>>>>I think the problem is related to the FTS4060.  During the brown out my
>>>>computer and the SR620 counter reset, but the two green LEDs on the 4060
>>>>stayed on, at the time my thought was "cool".  But the yellow "Align"
>>>>light behind the door has turned on and so far I have not been able to
>>>>get it to turn off.  But after trying a bunch of stuff the jitter value
>>>>is now back in the 9 ns area.  I have not been able to find anything in
>>>>the manual about operation with the "Align" light on and with the "Lock"
>>>>and "AC Pwr" LEDs on.  Does anyone have any ideas about it?
>>>>
>>>>On the rain thing.  I think the key parameter of water that matters is
>>>>the dielectric constant which is about 80.  The propagation constant is
>>>>proportional to 1 / SQRT( e ) or about 11% of what it is in air.  If
>>>>it's 1 ns per foot in air then it's 8.9 ns per foot in water
>>>>
>>>>I haven't figured out how to calculate the total volume of water in the
>>>>column between the satellites and the receiving antenna.  I did find a
>>>>web page that shows the terminal velocity of rain and it varies from
>>>>0.02 MPH for small drops to 20 MPH for big drops.  But this would need
>>>>to be coupled with the rate of rain fall (inches/hour) to determine how
>>>>much water was in the column.  Assuming big drops (20 MPH = 352 IPS) and
>>>>0.1 IPS rain rate says that the rain takes up 1 part in 3520.  If the
>>>>height of the rain is 20,000 feet then there's 5.6 feet of rain for a
>>>>delay of 50.5 ns???
>>>>
>>>>Have Fun,
>>>>
>>>>Brooke
>>>>
>>>>Tom Van Baak wrote:
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>>>>Rain should have an effect on the timing of the signal, since the
>>>>>>propagation speed of radio waves through water is different from that
>>>>>>through air. It will also attenuate the signal, causing worse S/N
>>>>>>ratio which would cause the lower-elevation satellites to not be seen.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>>David,
>>>>>
>>>>>Maybe we can figure this out. First, the refractive
>>>>>index of water is about 1.3. So I think this means
>>>>>the propagation speed of radio waves in water is
>>>>>down to about 0.75 c, right?
>>>>>
>>>>>Then, how much water are the GPS signals traveling
>>>>>through? Let's assume the typical amount of rain in
>>>>>a heavy storm is a couple of inches. All that water is
>>>>>either puddles already on the ground, drops on their
>>>>>way down, or moisture still in the clouds waiting to
>>>>>come down.
>>>>>
>>>>>The total amount of water in a cross section column
>>>>>of the atmosphere that the GPS signals travel though
>>>>>is thus a couple of inches total, max. Let's assume
>>>>>a worst case -- 6 inches.
>>>>>
>>>>>So, those GPS signals go through 20,000 km of
>>>>>empty space and atmosphere containing a total of
>>>>>6 inches of water; in which it slows down by 30%.
>>>>>At a ns/foot, this comes to 25 ps per inch of water
>>>>>content in the air; a total of 150 ps in my worst-case
>>>>>example above.
>>>>>
>>>>>My conclusion is that rain or snow, light or heavy,
>>>>>has no effect, even at the ns level. Can someone who
>>>>>really knows double check this back of the envelope
>>>>>calculation?
>>>>>
>>>>>Thanks,
>>>>>/tvb
>>>>>
>>>>>
>>>>>
>>>>>_______________________________________________
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>-- 
>>>>w/Java http://www.PRC68.com
>>>>w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
>>>>http://www.precisionclock.com
>>>>
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>>>>
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>>>
>>>      
>>>
>>-- 
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>>w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
>>http://www.precisionclock.com
>>
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>  
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