How to Maximise the Range of an GPS RTK System.

The range of an GPS RTK system can be extensive. It is not unusual to have a range of up to 4 miles. However sometimes this range can be severely reduced by interference on the radio channels that are used with this surveying equipment.

 

But how do you get the maximum range from your GPS RTK System? Follow these rules and you will be well on your way getting the most from your GPS RTK System.

1. Positioning of your Antenna for maximum range.

2. Type of Antenna to use.

3. Available Frequencies.

4. Equipment Condition.

 

1. To get the maximum range from radio waves you need to position the antenna as high above the ground as possible. Radio waves cannot penetrate through the ground so the positioning of your antenna is critical. If you can try to get a clear line of sight between you and the radio, a telescopic tripod or pole will help you to get the best performance.

2. Use a "mobile whip" antenna instead of the "rubber duck" type antenna. The mobile whip type antenna provides much better range than the rubber duck type.

3. Most GPS RTK systems use the PDL Radios produced by Pacific Crest. These PDL radio's have a function that can scan the available frequencies and select the one with the least amount of interference. Thus maximising the range the of the RTK GPS systems.

To scan the radio frequencies with the PDL radio, first set up your base station and power up the PDL. This will default to the last channel that was used. To scan the available frequencies, hold down the CHANNEL button until a small b appears in the display. Channel "b" is at the end of the channels 1 to 15. The PDL will then cycle through all available 15 channels and will then default to the channel with the least interference on it. This process will take around 10mins to complete.

Then you need to identify the channel that has been selected by the PDL and set the radio on the TopSURV controller.

To do this go into the GPS Status page, and click on the Topcon Icon in the top left hand corner and select Configure Radio from the drop down menu. Then select the base radio to configure and then select the channel that the PDL radio has selected and click Start Radio. For more information on this see this Guide to configuring the radio channels on Topcon TopSURV.

You should then have a radio link between your Rover Unit and the Base Station.

4. The condition of your is also vital to maximising the range of your GPS RTK System. You should consider the following as potential issues that could hamper your working range.

How old is the battery you are using? All “12V” batteries output 13.8V when new but their maximum voltage drops with age. Batteries can typically have around 300 charge cycles before they lose the ability to output the 9V required by most radio modems for transmission. This can occur within two to three years of normal use. It is also worth mentioning that batteries can eventually reach a point in their lives when they can still output 9V during the radio’s receive cycle but fail to deliver 9V during the radio’s transmit cycle. The radio will receive properly but its transmit range will drop significantly. Unfortunately, standard voltmeters cannot tell you if a battery’s output voltage is less than 9V during the radio’s transmit cycle because the transmit cycle (about 1/10 second) is too short. It is recommend to replace your batteries after 300 charge cycles or every two years.

What is the temperature? Extreme high or low temperatures can reduce your battery’s power output.

What is the condition of the cable to your radio? The battery may fail to deliver full power if the cable
is frayed, cracked or damaged.

If you follow the tips above then you should get the maximum range possible from your GPS RTK system.