Introduction:
This Application Note is designed for customers who are looking to test their GPS antenna performance using Siretta Modems.

Requirements: –
• Siretta GPS Modem (ZETA-G-UMTS or ZETA -G-GPRS) for this guide ZETA -G-GPRS used. https://www.siretta.com/products/industrial-modems/3g-mobile/entry-level-3g-with-gnss/
• ZETA quick Start Guide https://www.siretta.com/?smd_process_download=1&download_id=3630

• PC with Tera Term Version 4.96 , ( Tera Term can be downloaded from the following link https://osdn.net/projects/ttssh2/downloads/68252/teraterm-4.96.exe/) , it is freeware.

• PC with VisualGPSView. (VisualGPSView it is free application, it can be downloaded from the following link http://www.visualGPS.net for Windows 7 to Window 10.
• RS232 to USB cable (it comes with the Zeta starter kit Siretta Part Number: 60793).
• GPS antenna to be tested, for this Guide Mike 3a was used terminated with SMA Male connector. https://www.siretta.com/products/antennas/mike-3a/

Procedure for testing GPS antenna performance.

1. Connect ZETA-G-GPRS ( or any Siretta GPS modem) Modem to the PC using USB to RS232 cable supplied by Siretta.
2. Power on the Modem.( refer to modem Quick start guide)
3. Open TeraTerm window from the PC connected with the modem.
4. Select Serial , you should see “ Prolific-to-Serial Comm Port” as seen below.

5. Open setup tab on the tera term then select serial port, you will be presented with the screenshot below.

6. Enter Baud rate of 115200, Data 8bit, Parity none, stop 1 bit and flow control none as seen below.

7. Click OK, the Tera Term window will open where you can type AT command.

8. Send below commands
AT (You will receive OK)
AT$GPSP=1 (You will receive OK)
AT$GPSNMUN=3,1,1,1,1,1,1 (You will receive CONNECT)
Then GPS strings will appear as seen below.

9. Click file tab on the Tera Term window , select disconnect as seen below.

10. Once disconnected from the Tera Term, Open Visual GPS View from the same PC connected with the modem and you will find Menu Bar as seen below.

11. Navigate to the tool then select “Connect to GPS “option as seen below.

12. Pop up screen below will appear, select com port 3 and enter the baud rate of 115200 then click OK.

The setting now is complete.

13. Connect the GPS antenna (for this guide Mike 3a) to be tested to the modem GPS connector then click “Front Panel Status” from the Visual GPSView where you will be presented with below results.

NOTE: –
• GPS reception is affected by line of sight to the satellite.
• You should adjust the GPS antenna position to find best reception which will ideally be outside or close to a window.
• If comparing antennas, you should therefore always place the antennas under test in exactly the same location every time to ensure a fair comparison.
Excellent Performance

Figure .1

Disconnect the GPS antenna (for this guide Mike 3a) from the modem GPS connector then click “Front Panel Status” from the Visual GPSView where you will be presented with below results which show poor performance.

Poor Performance

Figure .2

14. Results from VisualGPSview can be analysed by observing the GPS Quality entry as below: –
• GPS Quality: Invalid meaning that Poor GPS antenna performance or GPS antenna is not connected to the Modem or GPS antenna Faulty (see figure 2 above.
• GPS Quality: GPS Fix meaning that Good GPS antenna Performance (GPS fix is the locational information that the GPS system provides for a specific point) see figure 1).

Note: – DOP (Dilution Of Precision) is an indicator of how accurate the GPS signal results are.
A low DOP value (0.9 – 99) means an accurate GPS signal result (see Figure 1), whereas a high value of DOP means an inaccurate GPS result (see figure 2).
If two antennas give the same GPS results, the antenna with a lower DOP value is more accurate than an antenna with a high DOP value.

Definition of terms used in VisualGPSview

GPS – Global Positioning System.

GLONASS – GLObal NAvigation Satellite System.
LATITUDE – is a geographic coordinate that specifies the north to south position of a point on the Earth’s surface.
LONGITUDE – is a geographic coordinate that specifies the east to west position of a point on the Earth’s surface
DOP- Dilution of Precision or GDOP Geometric Dilution of Precision is a term used in GPS and geomatics engineering to specify the error propagation as a mathematical effect of navigation satellite topology on positional measurement precision.
PDOP – Position (3D) dilution of precision
HDOP – Horizontal dilution of precision.
VDOP – Vertical dilution of precision
Satellites Tracked – Satellites Tracked by receiver
Satellites in View – Total satellite in View
GPS Quality – GPS Fix (Good antenna performance) / Invalid (Poor antenna performance/ antenna not connected / Faulty antenna).
Scatter Plot – The scatter plot shows individual position samples referenced to several type of reference types, next sample, average or user defined
Signal Quality/SNR Window – Monitor satellite signal to noise ratios and see them graphically on the screen. The signal quality window will grow or shrink to accommodate number of satellites in view

More information about modems can be found from https://www.siretta.com/products/industrial-modems/

More information about GPS antenna can be found from https://www.siretta.com/products/antennas/antenna-selector/

Any queries please contact support@siretta.com