Hi Bob,
The elevation mask is handled by the receiver, but I was wondering about
the s/n or signal strength. But it seems unlikely that all the
satellites would simultaneously fall below the magic threshold. In any
case, I will capture the data and see if there's anything interesting.
Thanks,
Ed
On 11/6/2012 5:55 AM, Bob Camp wrote:
Hi
GPS receivers have gotten better over the years. The early Motorola receivers
were relatively deaf compared to a TBolt. A TBolt is a bit deaf compared to a
LEA5-T.
My bet for the actual problem is that HP is doing elevation masks and s/n
detection in their firmware rather than in the receiver.
Bob
On Nov 5, 2012, at 10:11 PM, Ed Palmer <ed_pal...@sasktel.net> wrote:
Hi Azelio,
On 11/5/2012 4:09 PM, Azelio Boriani wrote:
Very interesting... is it using the binary protocol?
Yes, standard Motorola binary format.
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.
The link is TTL, not RS-232. The power supply to the VP is 4V93 and the logic
levels on the scope are maybe 0V2 and 4V8 so no problem there.
I've tried disconnecting the 1 PPS and/or the data line from the VP to the
Z3801A. The Z3801A reports the loss of 1 PPS quickly, but in either case,
waits for quite a while before getting upset. I haven't been able to corrupt a
message to see what effect that has, but I think it would have to be a very
specific form of corruption to be accepted. In any case, although that might
explain the drop to zero satellites tracked, it wouldn't explain the situation
where the VP reports fewer satellites tracked than the Z3801A does. This
occurs frequently. I don't know if the two situations (drop to zero and fewer
satellites) are related or not.
By the way, I was initially using SynTac and Z38XX to gather the data. Since I
couldn't believe the results, I replaced both with a program I quickly hacked
together to gather and parse the raw data from both units. The results were
the same.
Ed
On Mon, Nov 5, 2012 at 10:38 PM, Ed Palmer <ed_pal...@sasktel.net> wrote:
I've had a Z3801A for about a year. It's always had an issue where the
number of satellites tracked will drop to zero for one or two readings and
then jump right back where it was ( often at 5 or 6 satellites ). This
often (but not always) affects the EFC and/or PPS and/or HUP. My Tbolt is
running on the same antenna via an HP58536A splitter with no problems.
I've changed cables and splitter ports with no improvement. I've also
checked the power supply voltages and the frequencies of the two crystals
on the Z3801A board. All are fine.
I assumed that the VP was flaky so I recently pulled it out for testing
and found no problems. I then tapped into the link between the VP and the
Z3801A and found that the number of tracked satellites reported by the
Z3801A is often less than the number reported by the VP. Specifically,
I've seen the VP report 6 satellites tracked at the exact same second that
the Z3801A is claiming that there are no (zero) satellites tracked.
Does anyone know if there are any hidden parameters that the Z3801A is
using to decide if a satellite is acceptable? I looked through the manual
but I couldn't find anything. Is there a command I'm missing?
Thanks,
Ed
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