User's Manual

UtiliNet® Endpoint User Guide 1-5-2007
Page 21 of 30
© Cellnet 2005
Although the map data is usually provided from MapInfo on a CD ROM, it can be transferred to a hard
disk.
• Additional computer hardware will be required to run the MapInfo application.
For additional information, contact MapInfo
MapInfo Corporation
One Global View
Troy, New York 12180
Tel: [phone] or 800.FASTMAP
Fax: [phone]
Web: http://www.mapinfo.com
Email: [e-mail]
RF Considerations and System Design
Many books have been written on the subject of RF Considerations and System Design, but this section
covers the important fundamentals.
Radio Link Budget
Link Budget is a term used to describe a radio link from transmitter to receiver, and all of the factors in
between. Link budget analysis uses a simple method of allocating appropriate factors to each portion of the
link and then algebraically adding these factors. Then, the proposed link can be evaluated by how many
dB’s are left over. To analyze link budget, you must look at each component of the communication system.
Examine a sample radio link budget. Table 8.3 on page 8-9 summarizes the results.
Transmitter
For the UtiliNet product line, transmit power is +20 dBm nominally (100mW). The production minimum is
+18 dBm. It is not unusual for a radio to measure +21 to +23 dBm.
Transmit Antenna
Frequently, antenna manufacturers will not advertise the unit of measure associated with antenna gain of
their products. The commonly accepted unit of measure for antenna gain in the land-mobile industry is
dBd, which refers to dB of gain relative to a dipole. If there is a doubt, this should be confirmed with the
manufacturer. For our analysis, we need the dBi unit of measure, so a conversion factor is needed. The
conversion factor is +2.15 dB, rounded to 2 dB for this example.
Example:
A “3 dB omni-directional” type antenna is used. The antenna gain may be stated as 5 dBi. The “3 dB omni-
directional” antenna here refers to a very common, low cost antenna design consisting of a 1/4 wave
element, a phasing coil, and a 5/8 wave element, over a large ground plane. Such antennas perform well,
and are readily available from a variety of sources. It is a standard antenna for many applications, including
land mobile radios and microcellular base radios. Refer to "Use of Directional or Gain Antennas" on page
8-14 for pertinent FCC restrictions.
Ground Plane Effects
In the example above, ground plane refers to the flat, horizontal, metal chassis or enclosure to which the
antenna is secured. The ground plane works in conjunction with the antenna’s vertical element(s) to form a
complete antenna. Some types of antennas need a large ground plane to function properly, and some need
no ground plane.