Magellan ProMark3 RTK User Manual download pdf (Page 8)

Because the receivers in the RF53’s are quite sensitive, they work with

less than optimum Fresnel Zone clearance. But we can not over emphasize the

importance of having our antennas as high as possible. Antenna elevation rules

in the expected range equations. More power is more better, but at 900 MHz

high power just can’t make up for obstructions in the Fresnel Zone.

The best solution is to raise the base radio antenna as high as possible

above the ground. (For safety and convenience reasons, we can’t raise our rover

antenna higher than 6 feet.)

But how can we raise the ProMark 3 RTK radio antennas high above the

ground? The cable is only 4 feet long!

Move Your Base to Higher Ground

Works great when possible.

Modem near PM3, Move Antenna Higher with More Antenna Cable

Another method would be to add a coaxial cable between the antenna

and the RF connection on the transmitters. Unfortunately, coaxial line losses at

900 MHz just plain suck (about ½ power loss in 14 feet of RG58 at 900 MHz!)

Any benefit that we might achieve by raising the antenna will be more than lost

in driving the coax extension.

Better Antennas

We might replace the 1/4 wavelength end-fed dipole antennas with a

more directional antenna:

A 5/8ths wavelength end fed dipole might be a good solution; however it

would require an antenna matcher at the feed point. This won’t provide a good

match over the entire hopping frequency range and will significantly increase the

cost.

A multi-element Yagi beam antenna. While large gain is possible, we

would need to have the base and rover antennas pointing directly towards each

other throughout the survey day.

Adding more gain to the antennas will eventually result in an effective

radiated power that exceeds the FCC limits for unlicensed operation.

Raise the Radio Modem

I think the most successful method is simply raising the entire radio as

high as possible. To do this we can extend the power, TXD and RXD connections

to the radio (I added 30 feet of extension cable).

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Magellan ProMark3 RTK User Manual Page 8