GPS upgrade
 

Hi All!

I have a Standard Horizon GPS 150. (Couldn't afford color)

This summer I noticed that it, and one on our work boat, were slow to aquire. I called Standard Horizon and got a real human being who was very helpful.

He sent me an e-mail with instructions for a reboot of the unit. This did not work. His second suggestion was to contact C-map and ask for upgrade software for the unit.

C-map sent me a chip ($49.95, refundable after it's return and $4.95 S&H) that I put in the unit and in 30 seconds it was fixed. The GPS now aquires in less than 30 seconds from pushing the ON button.

This worked on both units that were giving me problems.

Good people, cheap fix.

Misty Blue

GPS signals different?
 

Misty Blue, that's very interesting. I have two Raymarine GPS units and both of those have been very slow to acquire all year (sometimes more than 30 minutes!) I wonder if something has changed in the transmitted signals requiring software changes on most consumer units? Anyone else experience the same problem?

Funny you should mention that, I have a new Raymarine RC400 handheld and it is slow as can be to aquire yet my two Standard Horizons (155C and 175C) aquire almost instantly. I did have an antenna croak on the 155C though.

I have a Standard Horizon 155C and haven't noticed any increase in its acquisition time. It seems to acquire very quickly. Our Lowrance iFinder GO2 handheld GPS acquires quickly too.

Newer software?
 

We have three Standard Horizon 150s. Two were installed about four years ago and one two years ago. The newer one was OK. Both of the older ones were the ones that did not aquire. Maybe the signals changed and no one told the older machines but the newer one understands the technology better than the old guys. Kind of like kids and cell phones!

Misty Blue

Corrected/updated satellite positions ?
 

I'd have to review some reports to see if this makes sense but ... I thought the GPS receiver remembers where it was when it was last on. Based upon that info and a database of the satellite orbits (ephemeris data) it tries to acquire those satellites which that it calculates can be "seen" and not those below the horizon. Once acquired, the satellite's true position is received from the transmission. So I'm guessing that (due to drag and other things) the stored ephemeris data becomes out whack with the true oribits and results in slower acquisition. Same thing happens if you move the GPS receiver when it's turned off, it takes longer to acquire from it's new position. Loading the receiver with newer, updated satellite orbit data restores the quick times. Brandy new units already have a "good" database and so don't suffer (right now) from this problem. When I get a chance I'll see if this is more than just a guess.

[Edit : Did some research and I'm no longer sure the above is plausible. See follow-up post]

makes sense
 

M-n-M, you may be on to something. That could explain it! Both units were quick when new, but they are now a few years old and have not had updates.

The older one (4 yrs) would require a flash ROM update at the factory, but he other one (3 yrs old) is upgradeable through the NMEA connector via a PC. I just need to find a cable. They both are not on the lates software rev anyway.

A swing and a miss
 

Well I looked into it some more and I'm now thinking the reason I stated above just isn't going to fly. As best as I can tell all GPS receivers download (and store) a new database of all the satellite's orbits (what I called Ephemeris data above but is properly called Almanac data) whenever they get a lock on any single satellite. A receiver also gets that satellite's precision orbital data (properly called Ephemeris data). Stated another way, each satellite transmits a message containing, among other things, a coarse/"imprecise" database of all the orbits (the Almanac) and a very precise position (Ephemeris) for itself. The Ephemris data is considered stale after 30 seconds and the Almanac after a few months. So if your GPS looses lock but regains the signal before 30 secs, the time to compute a new position is pretty much instantaneous. If you loose lock for more than 30 secs it'll take at least 30 secs (the time it takes for a satellite to send it's complete message) after you regain signal lock to fix your position. If you have turned off your GPS for several months it may take even longer as the receiver's data on which satellites are best to track is out of date. And as I stated before if you move your GPS since it's last lock, it'll take a "long" time for the same reason. All this said, I can't figure out a good reason why time-to-first-fix should have changed this year vs last year. Perhaps for on turn-on #1 but thereafter it should have been the same (because the Alamanac had been updated). Perhaps something did change in the downlink (though I couldn't find it) or perhaps it's some programming bug in the GPS's firmware. Got me :confused: , I guess so long as it is now fixed it's merely of academic interest.

Thanks for the update Mee-n-Mac. There may still be some relevant issue to the info you're providing here. It could be that the internal backup battery that keeps the flash memory alive may have died. In which case, it probably reverts back to the 4-year-old EPROM memory for the initial data load, then it has to load almanac data, then ephemeris. I'll contact the factory to take a look.

Thanks