[time-nuts] FTS4060 Continuing Saga
brooke at pacific.net
Mon Mar 6 12:54:46 EST 2006
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.
>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.
>----- 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
>>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???
>>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.
>>>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
>>>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
>>>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
>>>time-nuts mailing list
>>>time-nuts at febo.com
>>w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
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