[time-nuts] FTS4060 Continuing Saga

NE8S ne8s at earthlink.net
Mon Mar 6 13:29:31 EST 2006


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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