Title

Logging GPS event data with Ashtech GG24

Notes on instrumentation support

By
O.M.

Date
27 Nov 2012

Version
0.1

INTRODUCTION

These notes were made in preparation of the RV "Maria S. Merian" OBS survey in January 2007.

Start Ashtech Hyperterminal session, and confirm some important settings

A Hyperterminal shortcut icon has already been made and placed on the desktop. Double-click this icon:

The Hyperterminal program will first ask some silly questions. Press Cancel:

And you need to confirm cancel:

It seems unwilling to give up, but just press OK:

Now, at last, you are allowed to enter the program. Notice information in the status bar below: You are connected, and parameters are 9600, 8-N-1:

To be able to communicate with the Ashtech GPS, some settings are crucial. Confirm these settings by selecting Properties

Select the "Settings" tab:

Then select "ASCII Setup

Ensure that Send line ends with line feeds and Echo typed characters locally are selected, then press OK:

Setup Ashtech GPS

First reset the GPS, by issuing the $PASHS,RST command. The GPS will respond with a confirmation message $PASHR,ACK*3D for every valid command. Note that in the first case below, there was a typo, and even if you press Backspace and correct the error, Ashtech GPS still will not accept the command. It then says: $PASHR, NAK*30

Now enter the following commands. Ensure you receive $PASHS,ACK*3D on everyone.

  ----------------------------------------
    Command            Explanation
  ----------------------------------------

  $PASHS,SYS,MIX       Set receiver in mixed GPS/GLONASS mode
  $PASHS,PEM,5         Set satellite elevation mask to 5 degrees (satellites lower then this is ignored).
  $PASHS,PHE,F         Set event marker signal (i.e. GUNCO "FTB Scope" signal) to falling edge.
  $PASHS,NME,TTT,C,ON  Output Event marker message on port C
  $PASHS,TSC,GPS       Output Event marker time in GPS-system-time.
                       Current difference between GPS and UTC time is 14 seconds. GPS time is leading.
  $PASHS,NME,GGA,C,ON  Send NMEA message GGA on port C
                       See two pictures below.

After you see that time stamping works as expected, activate the NMEA GGA sentence so that we also receive location information. Write

 $PASHS,NME,GGA,C,ON:

Capture data to file

Select Transfer -> Capture Text ..., as shown below:

Provide a filename. Remember to give .txt extension:

If you want to stop logging, select Transfer -> Capture Text -> Stop:

You must confirm data capture to file, using Windows Explorer (shortcut icon should already be on desktop):

Just open the file:

Notice how the difference between GPS- and UTC time manifests itself. GUNCO shot events are given in GPS time, and the $GPGGA time is in UTC. Current difference (2007) is 14 seconds:

In case you need to alter/setup a Hyperterminal session

First ensure you are Disconnected, otherwise you are not allowed to alter hardware parameters:

Select File -> Properties ....:

Then select proper COM port:

Configure this COM port:

Use settings as shown below, in particular, use None for Flow control:

Then connect, by selecting Call -> Call:

Normally, this setup is not needed, but you never know ...

O. Meyer, 20. November 2006