Xircom An Intel Company GEM3501 User Manual
Core Engine GSM/GPRS Modem Developer Guide Preliminary Draft: 7/6/2001
59
Part Number: 07100026, Revision: 002
Confidential
© 2001 Xircom, Inc., an Intel company All rights reserved.
All trademarks and copyrights are the property of Xircom, Inc., an Intel company
All trademarks and copyrights are the property of Xircom, Inc., an Intel company
15.5 Formula Examples
15.5.1 Example 1:
The installer has a nominal 7dB gain antenna, is using RG-223 cable, and is using the
modem in a fixed application.
modem in a fixed application.
G = 7 dB
p = 7 dB
a = 0.29 dB/ft
then Attenuation needed = 7 – 7 = 0 dB
and L = (7 – 7) / 0.29 = 0 ft
In this example, the length of cable the installer must use does not matter because he
does not need any loss in the line to meet the FCC requirements.
does not need any loss in the line to meet the FCC requirements.
15.5.2 Example 2:
The installer has a nominal 7 dB gain antenna, is using RG-223 cable, and is using the
modem in a mobile application.
modem in a mobile application.
G = 7 dB
p = 3 dB
a = 0.29 dB/ft
then Attenuation needed = 7 – 3 = 4 dB
and L = (7 – 3) / 0.29 = 13.8 ft
In this example, the installer must use at least 13.8 feet of cable or use a 4 dB “in line
attenuator”, or a combination of the two.
attenuator”, or a combination of the two.
15.5.3 Example 3:
The installer has a 10 dB nominal gain antenna, using RG-223 cable, and the modem is in
a fixed application.
a fixed application.
G = 10 dB
P = 7 dB
a = 0.29 dB/ft
then Attenuation needed = 10 – 7 = 3 dB
and L = (10 – 7) / 0.29 = 10.3 ft
In this example, the installer must use at least 10.3 feet of cable, or use a 3 dB in line
attenuator, or a combination of the two.
attenuator, or a combination of the two.
NOTE: The installer is responsible for assuring that the proper antenna, cable
length, and / or attenuation, is installed correctly, so that the limits of FCC §15.203
are not exceeded.
length, and / or attenuation, is installed correctly, so that the limits of FCC §15.203
are not exceeded.