budgie wrote:
On Thu, 05 Jan 2006 03:12:07 GMT, MetalHead
wrote:


Chuck S. wrote:

OK, one more question, do you need the RS-232 port if you only want to lock
a vcxo to the 10kHz? My guess is no, just +5 volts and ground, and take the
10kHz from pin 20 of the connector.

I have used the older Rockwell GPS stuff and they seem to need to have a
recent almanac transferred to them before they will get a fix. Rockwell
used to distribute a freebie software package that would help you deal
with all the setup stuff. It was called something like Lab_10 or Lab_X
or somesuch. The newer stuff may need less handholding.


That's an interesting observation, Bob. I was watching the NMEA output from
power-up on the Jupiter I am using doing a "frozen start" out of the box without
an antenna. One sentence showed it checking each sat in turn. When it finds
one (which it obviously doesn't do with no ant) it assigns a Rx channel# to it.

When I finished play mode on the pooter end and connected an ant, it went
through each bird in turn, about one per second. So within a minute it had
acquired a set of birds and began processing. As I am using no form of backup,
the Jupiter starts from ROM each time and does a similar "frozen start" i,e,
factory almanac). It consistently achieves a full fix in under 3 minutes.

This surprised me also. As I mentioned earlier, these two system that
this showed up on were very old, 5 channel receivers.

Sitting outside, with a clear view of the sky, the receivers would
search through one sat at a time and find one occasionally, but they
would lose them after several minutes. After a couple of hours, they had
not acquired and held enough SV's to get a fix at any time.

I loaded up an almanac through the tool and either receiver would get a
fix within a few minutes and hold it for the half hour that I left them
to run.

I am assuming that these receivers were running out of ROM as well. Some
GPS systems put an almanac in ROM to improve the cold start fix time,
but I don't know if these are among them.

As for the original poster's other question about needing an antenna, I
would say that unless there is one on the Jupiter board, then yes.

Bob