Permanent GPS Stations - Comms - Radio Modems

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Permanent GPS Stations - Comms - RadioModems

Wireless technology offered by radio modems provides an effective data throughput ( 2.4-19.2kbps) using a carrier-independent mode of transmission over distances of up to 100 km so long as line-of-sight is maintained. For remote sites, this may be the only alternative to ensure regular data downloads. Radio modems require an external antenna for transmission and, therefore, inter visibility between the receiver and download sites is required. For truly remote sites, consideration should be placed on high power antennas, radio repeater sites, or the use of in-line amplifiers to boost the range and data throughput. Inquire with local communication licensing authorities regarding the use of high-powered radio communications. Another option for enhanced communications is the choice of a directional (Yagi) antenna over an omnidirectional one, particularly if only one leg is required between the master and slave.

The initial investment for a radio modem is relatively high (2 to 3 times the cost of a phone modem), but the cost is somewhat offset by the fact that, once installed, the user does not incur additional toll charges for each connection. A mixed communication mode may also be a viable alternative where a remote radio link is connected to a remotely located phone line. The modems are divided into types according to modulation and frequency range.

Modulation Types

Direct Sequence Spread Spectrum
Frequency Hopping Spread Spectrum
Narrowband

Frequency Ranges (modems operate unlicensed in the following ISM bands)

915 MHz (902-928 MHz)
2.4 GHz (2400-2483.5 MHz)
5.8 GHz (5728-5850 MHz)

For interfacing with GPS receivers, the modems have to be RS-232 compatible.

Suggested minimum requirements

Range up to 60km (Line-of-sight)
Low power consumption (2-5W)
Light weight (0.5-1.0 kg)
High effective data throughput (2.4-19.2kbps)
Environmentally durable (temperature, humidity, shock resistant)
RS-232 compatible

Below are suggested generic register settings for using the DGR-115H with a GPS receiver. Included are settings for the remote and local radio modems, repeater modems (if necessary) and the receiver

For more information on the various settings and configurations for a radio modem currently in use at permanent stations, select from the list below. For example, the UNAVCO Boulder Facility is also using the DGR-115H in combination with Telebit Worldblazer (T3SA) phone modems in applications where a remote radio link is connected to a remotely located phone line. This mixed communication mode varies slightly from a direct radio link.

Remote Communications Configurations

Trouble shooting tips: Confirm that the appropriate call-book numbers are included in all radios and that the RF transmit power is set appropriately for your application. Also, make sure that all radios in your link is set to the same frequency key. When operating with several slaves and one base modem (Mode 6) make sure the base modem is set to Point to Point Slave/Master Switchable (Mode 6) and the slave modems are set to Point to Point Slave. Consult the User Manual for details.

Send questions or comments to Support (supportunavco.org)

Last modified Thursday, 25-Jan-2007 23:56:48 UTC