On 11/5/2012 11:27 PM, Hal Murray wrote:
azelio.bori...@screen.it said:
Very interesting... is it using the binary protocol? Maybe a serial link
error, the binary protocol has a checksum (yes, NMEA too). Check the serial
link levels with a 'scope, maybe that the Z3801 firmware waits to see some
consecutive errors before actually reporting that something is wrong,
meanwhile the satellite number is set to 0.
That seems unlikely, but I've been surprised before.
I have two Z3801As using the same antenna which is not in a good location.
They both go into holdover at the same time about once per day.
(Occasionally, it's only one.) I don't have any data on the number of
satellites. I assume it goes to 0, but I don't know how long it stays there.
It looks like a spike on the scale of 1 sample per minute.
I've been assuming it was something like multipath from an airplane. I'm
roughly 20 miles from the San Francisco airport. I'm not on a main flight
path, but it's not uncommon to see a large plane go over reasonably low. I
assume it's merging into the landing pattern.
Does anybody know how to find out if there are any planes near a specific
location, and if so how to get the flight path with good timings?
--------
The HP driver in the ntp reference package logs a line like this every minute
(actually 64 seconds):
56237 776.033 127.127.26.1 T2201211060012573001036 64 0
56237 840.033 127.127.26.1 T220121106001401300102D 64 0
56237 904.044 127.127.26.1 T2201211060015053001032 64 0
56237 968.034 127.127.26.1 T2201211060016093001037 64 0
The " 64 0" on the end are counters I've added to my local copy. The 64 is
the number of good T2 messages. The 0 is the number of messages with errors.
One of the columns in the T2 chunk is the FFOM, another is the TFOM. (I'd
have to look it up.)
If I was to add some more info to that line, what would you want? EFC and
number of satellites are a couple of obvious ones. EFC probably doesn't
change very often or fast. One sample per minute is probably good enough.
For the number of satellites, we might want both the min and max, and even
the count at that level.
EFC would be interesting to see. When the problem occurs on my Z3801A,
the EFC might do nothing, or spike, or jump and stay at the new value,
or jump and recover to the original value. HUP would also be good to
record to watch for a degradation in that value.
Ed
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