[time-nuts] How phase stable is rg59 or alternate coax
John Ackermann N8UR
jra at febo.com
Mon Nov 21 14:44:05 EST 2016
Several years ago I measured the delay of about 80 feet of LMR400
feeding a GPS antenna, much of which was lying on a black shingle roof
in the Georgia sun. I checked in early afternoon when the sun was
beating, and in the wee hours of the morning, to get the greatest
temperature delta. My recollection is that the tempco was surprisingly
small -- maybe a couple of nanoseconds. It was much less than the other
elements of the GPS timing error budget.
I can't find the data right now, but will keep digging. There's also a
short paper from the early 2000s from Haystack on their measurement of
LMR400 in an environmental chamber. They came to the same conclusion,
but I can't find that paper either. :-(
I don't know how much different RG58 results would be.
On 11/21/2016 09:38 AM, Scott Stobbe wrote:
> If you had 30 ft of rg59 outdoors seeing maybe 10 degC swings everyday,
> would the propagation time be stable to ps? ns?
> On Sun, Nov 20, 2016 at 7:04 PM Hal Murray <hmurray at megapathdsl.net> wrote:
>> Is that even a sensible question? Is there a better way to phrase it?
>> The problem I'm trying to avoid is that the weather and the satellite
>> geometry change over time so I can't just collect data for X hours, switch
>> the other antenna or move the antenna to another location, collect more
>> then compare the two chunks of data.
>> The best I can think of would be to setup a reference system so I can
>> data from 2 antennas and 2 receivers at the same time. It would probably
>> require some preliminary work to calibrate the receivers. I think I can do
>> that by swapping the antenna cables.
>> If I gave you a pile of data, how would you compute a quality number? Can
>> just sum up the S/N slots for each visible/working satellite?
>> These are my opinions. I hate spam.
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