Venus GPS unit doesn't fix

GPS/GNSS Development Boards
1

Hi all,

A few weeks ago I bought the GPS minipod, the one with the small PCB ceramic antenna, it couldn’t fix so I sent it back.

On the advice of the support rep at SF, I bought the Venus unit with the SMA connector and the ‘Antenna GPS Embedded SMA’ and it still won’t fix. Here is the NMEA output I’m getting:

$GPGGA,220645.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,0.0,M,0000*6A

$GPGSA,A,1,0.0,0.0,0.0*30

$GPGSV,1,1,01,13,00,000,32*4B

$GPRMC,220645.000,V,0000.0000,N,00000.0000,E,000.0,000.0,261009,N*7D

$GPVTG,000.0,T,M,000.0,N,000.0,K,N*02

As you can see it can’t find any satellites, I’ve done the RTFM thing (I have been known to not do this :slight_smile: ) and can’t find anything else I can do. I’ve even left it run for 30minutes and still no change.

A little about my environment, I’m sitting in the 30th floor of a condo pretty close to a window. I know it’s far from perfect but I figure my iphone can get a fix even in the elevator this unit would too, considering the antenna.

I might be a little off-base with this theory, and I’m relatively new to electronics having been a software guy for so long. Does anyone have any thoughts/suggestions?

2

Hi

A lot of people had similar porblems and i know one of them solved it by giving it more time to get a fix for the first time.

My advice would be to connect it to a battery, and leave it in open-air for about 30 minutes.

if all goes well your GPS should work

3

OK, will try that this weekend. Will post results.

4

FWIW, we are seeing the same problem on all the SF Venus 6 modules we have tested (along with some serious problems tracking velocity, but that’s a subject for another post).

If you sit an MTK-based module side-by-side on a window sill with a Skytraq Venus 6, the MTK will typically lock in well under a minute even from a cold start, but can take the Venus 6 ten minutes, and sometimes even longer than that. (this is with the embedded SMA antenna)

The Venus 6 fares much better when it is out in the open and not on a window sill. But on rare occasions we have still seen MTTF times of over 20 minutes (yes, 20 minutes) with a clear view of the sky.

The Venus 6 generally locks faster if it already has some idea where it is. If you aren’t using the backup battery input on the board, then it has to start over from scratch the next time you power it on. The SF board has a solder bridge jumper which, by default, connects the backup battery input (VBAT) to VDD. VBAT must not be unconnected, but if you do use a backup battery, you will need to desolder this jumper to avoid draining your backup battery onto the VDD rail.

Also, please check the soldering on the threaded connector for the SMA antenna where it is soldered to the board. We have had a couple modules shipped to us with cold solder joints, or with no solder at all on the center pin.

5

I modified mine to use a schottky diode and a small battery (the part off the datasheet I got from digikey).

It does take a while to coldstart, but one complication is “low power mode” will only use 2 “engines” to search, while normally it will use 4.

The newer chips that use 50+ engines are using them during the cold/warm start period to scan the entire band for satellites quickly. They aren’t needed once locked, but the TTFF will be much faster.

With the Venus, AGPS makes a night-and-day difference. If it knows the time (needs to see 1 satellite from a cold start), it will take 2 seconds while the AGPS data is valid and there is even a partial view.

For 10Hz, logging, AGPS and WAAS at the same time, the Venus is a great chip.

For frequent coldstart without AGPS TTFF, others do better.