Instruction manual

Radio Link Page B-1

Radio Link

Careful consideration must be given to the following situations to get the full performance

from the radio data link:

Data Transmission Rate

To provide real-time, accurate rover position solutions at a 1-second rate, the Real-time Z

system requires radios which can transmit data at a speed of at least 4800 baud. For best

performance, radios capable of a 9600 baud data link speed are strongly recommended,

especially for RTCM operation with type 18/19 messages. A high data link speed is

required since the base station has to transmit a large amount of data to the rover station in

each message it sends (both GPS carrier phase and pseudo-range measurements).

Line-of-Sight Transmission

Because of the high data transmission rate requirement, the Real-time Z system usally

uses radios operating in the VHF/UHF frequency range. These frequencies are

predominantly line-of-sight. The base station antenna should be placed as high as possible

for maximum range. However, this needs to be balanced with reasonably short radio

antenna cables, due to the relatively high transmission line loss on a cable when using

VHF/UHF frequencies. Foliage, buildings or desert terrain may shorten the transmission

distance while improvement may be found in transmissions over water, snow, or ice. The

following is a formula for computing the approximate line-of-sight distances that can be

achieved between the base and rover stations

where

d—line-of-sight distance in miles

h—base station antenna height in feet

K—surface reflectance coefficient, which is 1.33 for temperate climates (polar

climates will have larger K values).

3 K× h×

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