Steve Rooke skrev:
2009/7/4 Magnus Danielson <[email protected]>:
Steve Rooke skrev:
Attached plot of jump in my Z3805. Looks like there was a jump and
then then a rapid track back to the "normal" frequency drift. Comments
please?
Small picture, a bit hard to interprent. The green is?
I think I correctly interprented the length of the plot to a week (the lower
plot shows a regular pattern of 7 cycles and I think I interprent the red
text to day 168,71 hrs). If it would have been a frequency jump it would
track in faster than half a day. Can you come to think of something else
that could have happend to the equipment that day?
Your right, it is a bit small so I've managed to figure out how to get
the bigger picture (attached).
From the help help file of the application"
"Finally, graph mode presents a detailed graph of the EFC (electronic
frequency control), TI (time interval value), PU (predicted
uncertainty) and the number of satellites being tracked. The cursor
readout indicates the time and date, and either the EFC or the TI
corresponding to the location of the cursor.
On typical Z3801A's, measurements confirm that 1 count of EFC is
roughly equivalent to 1 part in ten to the twelve."
That clear up all those issues! Thanks! :)
The event seems to start at about 04:00 30/6/09 and is over at about
16:00 on 30/6/09. There is no indication that there was a complete
loss of lock to the birds at that time and the number of sats looks no
lower than at other times (OK it's not an ideal number of sats but my
antenna is in a temp position at the moment and cannot see all of the
sky).
Infact, if you look at the sat lock trace, you see the same pattern as
every other day. Your antenna position do make you loose sight of a few
birds as you can see very clearly as a type of sine-shaped pattern
occuring, but only the 24 hour occurences is as sharp, but you do see
the 12 hour pattern if you look a bit more closely.
The antenna position could improve, but I would not say it is the root
cause here.
There is no actual loss of lock, it shows that the peak
deviation at that time was about 35ns but obviously something changed
to cause the EFC needing to track away from the "norm" to remain in
lock. I think I spent most of that day in bed with the flu that's
going on here so it was very quiet. We have been having a fair bit of
rain here but it has been over many days, not just this Tuesday. Just
thinking now, but these times are in UTC so that would represent about
4pm on Tuesday to 4am on Wednesday, again most of time in bed.
Hmm. Hope you are clear from that flu now. Nasty buissness.
I don't think it is the crystal making a frequency jump, or is it?
Such a jump would be high-pass filtered by the locking PLL. Hmm. Looking
at the TI is looks like it starts with a steep slope, so it could be
such an event, or any other similar event. The EFC responce looks a bit
pale thought, so I wonder if that is really what happend. Need to ponder
some more.
Cheers,
Magnus
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