Owner's Manual

GDX-350 Sensor Transmitter
P/N: 5600-9001 Rev 2 21
Example:
The RF radio modem has the following parameters:
• Maximum RF TX power setting = 30 dBm (1 Watt)
• RF RX sensitivity = -100 dBm (this is a constant)
• Antenna gain (standard equipped dipole) = 2.1dBi x 2 = 4.2dBi
So the system operating margin is:30 - (-100) + 4.2 = 134.2 dBm
This is enough to transmit 10 miles if freespace was the only loss in the system. For this to be the case,
the antennas must be mounted with a combined height greater than 95 ft above all obstructions (including
the ground) to keep the Fresnel zone clear. In practice however, there are many losses in the system
besides just freespace and it is recommended there be at least 20dB extra system operating margin.
RF “Rules of Thumb”:
• Doubling the range with good RF “Line of Site” (LOS) requires an increase of 6 dB.
• Doubling the range without good RF LOS requires an increase of 12 dB.
2.5. Antenna Selection and Location
A site survey using an RF spectrum analyzer and test radios is highly recommended.
The location of the antenna is very important. Ensure the area surrounding the proposed location is clear
of objects such as other antennas, trees or power lines which may affect the antenna’s performance and
efficiency. It is also vital that you ensure the support structure and mounting arrangement is adequate to
support the antenna under all anticipated environmental conditions. The choice of appropriate mounting
hardware is also important for both minimizing corrosion and maintaining site inter-modulation
performance.
Most installations utilize locally mounted dipole antennas as shown in Figure 2-6. An option is available
for a 6 foot riser to increase the height of the antenna 6 feet above the GDX-350. Extreme cases may
require special order of directional antennas mounted in such a way to allow aiming towards the base
station antenna. Minimize obstructions between the GDX-350 and the base station antenna.
Figure 2-6: Local Antennas (900MHZ Shown)