How do I confirm my firmware revision on the GPS module?

The GPS modules do not come marked with the Firmware version. You can poll the software using Sirf Binary for the ISM300fx modules and use OSP (one Socket Protocol) for the ISM4xx version of gps modules.

If you want to run your GPS in Nema, you will need to switch to either Sirf Binary or OSP and send the module the message ID 132 – Poll Software version.

On the ISM300Fx how should I connect my antenna?

The RF in port on the ISM300 connects to the antenna (via the U.fl) or pad 1 and the input of the GPS. It is important to add the external LC circuit shown in the reference schematic on the specification because this will prevent the loss of GPS signal going into your power supply. One part we have used is the inductor L3 (33 nH is 0603HP-33NXGLW)

I need a 3 v or 5 v GPS module?

Use the ISM300f2-x family of GPS’s.

What application do you have to help troubleshoot the GPS design?

Ideally, if you can connect your PC to the UART for any of the ISM300x or ISM400x GPS modules you can run the Sirf Live. Sirf Live will show you all the satellites and C/no and allow you to send commands and become familiar with the GPS.

Simply contact sales@inventeksys.com for a free copy of the software.

Does the Sirf IV GPS modules have FCC/CE?

The FCC does not require that the GPS receiver has FCC or CE. We did perform FCC on the Sirf III for a specific customer request, however it is not required.

Does the ISM300x store Ephemeris data automatically?

Yes, if you use the battery back up feature and keep power alive the unit will store the data and provide warm starts. The ISM400x GPS do not require the battery back up.

How do you summarize acquisition sensitivity?

Acquisition sensitivity can be summarized in two  conditions: ephemeris available from any source, or ephemeris must be obtained from the satellite data stream. For conditions where ephemeris is available, we can acquire a satellite down to about -155 dBm.

When we must decode ephemeris, we can still acquire down to -155 dBm, but the signal must be much stronger before we can decode the data. 

That limit is -147 dBm in the latest release of ISM300x 9Sirf III

How does your GPS output the 1 PPS?

For the ISM300x and ISM420 GPS, we output the 1 PPS as follows:

The first output starts when we the GPS Kalman filter gets a stellite fix. Thereafter, the 1 PPS continues to  be output until the receiver is reset.  If we drop to less than 3  SVs, the Kalman stops using satellites and goes to DR mode.  At that  point, the 1 PPS is no longer steered but free-runs with the 49.107 MHz clock (triple the 16.369 MHz GPS clock). If the Kalman filter again starts using SVs, it will again steer the 1 PPS.

The pulse is 1 μs wide by default. We only have 12 pins on the ISM480 connector so we do not output 1 PPS.