All materials here are courtesy of Pat Crowe (email@example.com)
Download the Lassen SQ GPS Receiver System Designer Reference Manual and the SQ_Monitor.exe from the Trimble site.
Before you can connect a Trimble Lassen SQ to the GBA you first need to set the protocol for the serial output, from the factory default protocol, TSIP, to the protocol required by the GBA firmware: NMEA 0183.
To do this you need to first build an interface circuit to the pc (see diagram).
Then run SQ_Monitor.exe. Select 'Configure'...'Serial Port'... and make the selections shown in the screen dump. I chose 9600 Baud, though you could choose a different speed if you wanted.
Use HyperTerminal (set to this same speed etc) to check that you are receiving NMEA codes from the GPS module. Look at the System Designer Reference Manual to see what the messages should look like, and take a few moments to understand what information they contain, for your interest.
If you are receiving the correctly formatted messages, you are ready to connect the module to the GBA. Use the circuit shown. When making the map using 'gbagps.exe' remember to use the settings 9600 Baud, inverse - NO, parity - none, length - 8.
I built a very rough unit inside a sloping panel box from Maplin. You can see how I used an old link cable and wedged the connector in position with a cut-up plastic eraser. You can also see the 'Ultra-Compact Embedded GPS Antenna with an HFL connector' plugged into the Lassen SQ.
However I have done some testing now and unfortunately I find that with the SP screen fully open it is hiding the antenna from the sky!
It captures ok in a couple of minutes with the screen folded at 90 degrees, so it doesn't cover the gps box. But I wouldn't recommend making it like this. I guess Mikhail's approach is the right one, with the gps module on the end of a cable so you can position it separately.
When you buy the Lassen SQ, don't forget you need an antenna. You get get a Mag-mount antenna for in-car use, or an embedded antenna like the one shown. You will need to source an 8 way socket to connect to the module. remember you will need at least 2. I started with 5 and have one left now as they break easily.