I’ve managed to get my SUP500F talking to my PC using a MAX3232. At 1Hz I can get a 3D position fix, using the SkyTraq software to interpret the NMEA. Similarly I get a fix at 2Hz (changed by going to Binary → Configure position update rate → 2Hz → Update to SRAM). However, at any of the higher speeds I no longer get a fix (or any satellite link at all). I still get NMEA messages, just no fix. Changing back to 2Hz gets me an immediate fix.
I am in South Africa, so I don’t know if we have dodgy old satellites that don’t work at >2Hz, but that seems rather silly.
EDIT: Ok, should have known that GPS satellites are not geostationary… - so it’s definitely not due to dodgy satellites.
We definitely don’t have WAAS. I know the SUP500 has lots of issues, so might this be the problem?
Or is there something else I must change to make >2Hz work?
What’s your power source? It seems very strange that you can get a lock at 2Hz but not at higher update rates.
At 4Hz and up do you see NMEA data scrolling past in the SkyTraq software window? Perhaps it’s not so much a lock issue as it is a communication issue.
Just thought I’d close this off in case anyone else has a similar problem.
Details of the system:
I was powering the GPS with 5v, but 3.3v signalling (both with MAX3232 and PIC32 UART). I’m pretty sure this is acceptable from the spec sheet.
I continued to get NMEA info at all update rates, and at 10Hz the SkyTraq software automatically changed comms speed to 38400. Thereafter it stayed there (even when I decreased the GPS update rate). Definitely no comms problem.
I could switch 1Hz (lock) → 2Hz (lock) ->4Hz (no lock, even after 30 mins) → 2Hz (immediate lock). I did not power down between these switches, so almanac etc should still have been valid.
I emailed Sparkfun tech support, and they responded that this is one of the symptoms of this dud batch of SUP500’s. Maximum respect to them for swapping it out for me, excellent service. Seems that when this GPS works, it’s a great little unit. But the last batch had some duds.
SkyTraq sent me this updated firmware. I get up to 20Hz updates!!! (Which isn’t in the spec sheet) I’m not actually sure if it truly is updating at 20Hz but I configure it and it replies with ‘Successful’.