Usage
and Maximum Power Limit Guidelines in the US under FCC regulations
Before
we can go on, first we need to separate the two different classes of
users for Spread Spectrum devices that exist and set some guidelines
of some of the specs. Consumers
and IT Professionals Operating Spread Spectrum (DSSS) gear:
-
Users operate
under FCC Part 15 rules and regulations.
-
Frequencies
include 902-928 MHz, 2400-2483.5 and 5725-5850 MHz.
-
Maximum
Transmitter Power Output (TPO) is 1.0 watt or 30dBm.
-
The formula for
converting antennas from dBi to dBd is dBi-2.2=dBd.
There are two
different classifications for operation. You'll commonly hear these
modes referred to as Point to Point (PTP) and Point to Multipoint (PTMP).
PTP is when two sites talk only to
themselves. PTMP is when many sites talk to a single core
site. Each of these modes have different EIRP (Effective Isotropic
Radiated Power) limitations.
Point to MultiPoint:
Transmitter RF power Antenna Gain
EIRP in watts
30dBm 1W
6dBi
3.98
27dBm 500mW
9dBi
3.98
24dBm 250mW
12dBi
3.98
20dBm 100mW
15dBi
3.98
17dBm 50mW
18dBi
3.98
14dBm 25mW
21dBi
3.98
10dBm 10mW
24dBi
3.98
-
Losses from the
transmitter via cabling, lightning suppression, filtration can be
removed from the transmitted power dBm figure. An example
here would be say a 30dBm 1 watt amplifier with 100ft of LMR400 (at
6.7dB of loss) brings transmitter power down to 23.3dBm, allowing a
12dBi antenna.
Point to Point:
-
Higher EIRP
is allowed if the antennas are directional in nature.
-
Systems operating in a point-to-point
operation may employ transmitting
antennas with directional gain greater than 6 dBi provided the maximum output power of the
transmitter is reduced by 1 dB for
every 3 dB that the directional gain of the antenna that exceeds 6 dBi.
Maximum transmitter power versus
largest antenna table for PTP:
Transmitter RF power Antenna Gain
EIRP in watts
30dBm 1W
6dBi
3.98
29dBm 800mW
9dBi
6.35
28dBm 630mW
12dBi
10.14
27dBm 500mW
15dBi
15.81
26dBm 398mW
18dBi
25.23
25dBm 316mW
21dBi
40.28
24dBm 250mW
24dBi
62.79
23dBm 200mW
27dBi
100.2
This information is
provided as a guideline. If you are not a professional installer we
highly recommend that you read the FCC Part 15 rules and understand them
before attempting installations.
Amateur Radio
Operators operating under licensed spectrum:
-
Users operate
under FCC Part 97 rules and regulations.
-
Frequencies usable
from over-the-counter consumer gear include the 33cm 902-928
MHz band, the 13cm 2390-2450 MHz band and the 5cm 5650-5925Mhz band.
-
In the 13cm band,
802.11b/g channels 1 thru 6 are the only channels in the 2390-2450 MHz
bandplan.
-
Maximum
Transmitter Power Output (TPO) is 100 watt or 50dBm.
-
You must enable broadcasting of
your SSID, which has to include your callsign.
-
Encryption is not currently permitted.
-
Only authorized licensed
operators should be able to access Part 97 installed hardware, so care
should be taken to prevent unauthorized users from utilizing said
hardware.
It's highly suggested for Amateurs
visit the ARRL website and participate in the HSMM (high speed multimedia)
working group. The HSMM group only deals with working on high speed
data via Amateur radio. This group is producing proposed rule making
changes to be submitted to the FCC that would make operating simpler and
allow more reasonable usage of for example encryption. The author of
this document, Dave Anderson is a licensed amateur radio operator (KG4YZY)
and is on the ARRL HSMM Working group and a founding member of ARBA, the Amateur Radio Broadband Aliance. | 
