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7.
FCC
L
IMITATIONS
7.1.1.
FCC Part 15.231
The SubGig protocol is designed for low, non-ISM band frequencies subject to FCC Part 15.231
which covers the band between 70MHz-450MHz. The FCC allows for basic status and control
messages within this range but has limits on continuous transmission time and periodic
messages. Periodic messages, or messages that are sent on a pre-determined regular
schedule, are allowed for supervisory messages that are used to monitor the health and status
of the system. General purpose payloads can be send with periodic intervals but with certain
restrictions:
1.
The period cannot be less than 10 seconds
2.
The total transmission time cannot be greater than 2 seconds per hour. Note that this is
not possible with the SubGig protocol on the RBM101.
3.
The power output from the radio must be reduced to a lower FCC limit as compared to
standard event based messages.
Event based messages, in contrast with periodic messages, can be sent as needed and are not
subject to timing or restricted power level limitations. For any individual event the total
transmission time of the message cannot exceed 5 seconds, however similar to the 2 second
total transmission time for periodic signals, this is not possible to violate with the RBM101.
To illustrate the difference between periodic and event based messages, consider a simple
system that measures temperature. An event based system would send an alert if the
temperature changed by a minimum value or exceeded some threshold which would initiate
a transmission. A periodic system on the other hand may want to send temperature
measurements, say once per minute, regardless if the temperature has changed. In the event-
based scenario there are no limitations placed on the transmission in the protocol, but in the
latter periodic example the transmissions would have the limitations listed above.
Most IoT applications send simple status and control messages that fall well within the
limitations described in this section. The SubGig protocol is designed with these FCC limits in
mind and the RBM101 modules have features to prevent violation of these limitations as
described in the Governor section below.
7.1.2.
Governor
Proper system design is needed in order to ensure compliance with FCC limitations. In general,
best practice system design in the 315MHz band would use event based messages wherever
possible so as not to be subject to the power or timing limitations listed in the previous
section. Fortunately, the RBM101 modules have a governor feature which prevents a user
from exceeding the limitations.
