User's Manual

UtiliNet® Endpoint User Guide 1-5-2007
Page 23 of 30
© Cellnet 2005
along the path, distance, and other parameters can determine this factor. Typically, this factor ranges from 5
to 40 dB.
This factor, plus the free space path loss, gives total median path loss.
Example: Assume a path that is 5 miles long. One antenna is on a hill or water tank 300 ft. higher than the
surrounding area. The other antenna is on a 30 ft. support structure, for example on the rooftop of a 1 story
building. Except for the
Table 3.1 Free-Space Path Loss
hill or water tank, the terrain is considered relatively flat. The path loss adder term is -10 dB at 915 MHz,
according to the Okumura/Hata propagation prediction method using the suburban area model.
Receiver Antenna
The previously mentioned antenna considerations also apply here, including possible ground plane effects.
For this example, this is (again) a “3 dB omni-directional.”
Receiver Transmission Line Loss
The principles and goals here are the same as those for the Transmitter Transmission Line Loss term.
Receiver
Receive sensitivity for the UtiliNet product line is typically -107 to -112 dBm. Automated production tests
are performed on all deliverable radios at various frequencies, and with signal levels down to -104 dBm.
For this example, assume the receiver sensitivity is -107 dBm. This is a safe, conservative estimate for
current production radio sensitivity.
Noise Floor Factor
One of the factors that make the 800 to 900 MHz frequency band so attractive is the relatively low
equivalent noise temperature of man-made noise. For a noisy business environment, this has been estimated
to be 87 K at 915 MHz. Relative to an ambient antenna noise temperature of 298K, this translates to a noise
floor increase of 1.2 dB. Thus, we will allocate 1 dB (rounded to the nearest dB) of the link budget to
overcoming man-made noise.
Multipath Fade Factor