WIT2410P
2000- 2005 Cirronet
Inc
54
M-2410-0000 Rev F
Appendix II – Calculation of Maximum Transmit Duty Cycle
As outlined in Appendix I, each remote WIT2410P can transmit only once during a dwell time.
The maximum length of the transmitted packet from each remote is set by the system design
and cannot be adjusted by the user. That packet length is calculated as follows:
Preamble
9 bytes
Sync and CRC
10 bytes
Data Payload
13 bytes
Maximum packet length
32 bytes
Bit time
(1/460 Kbps)
2.1739 us
Byte time (bit time * 8)
17.3912 us
Maximum packet time (byte time * 32)
556.5184 us
The maximum amount of time that our Remote transmitter can operate in any 10 millisecond
period is 556.5 us. Therefore, our source-averaged transmit duty cycle becomes 0.0556 (556.5
us / 10 ms). Note that this duty cycle is not dependent on our use of Frequency Hopping. We
are not averaging our power over the number of hops. The above calculation is strictly based on
the maximum amount of time our transmitter can transmit in any 10 ms time period – regardless
of the channel the radio happens to be on at the time.
Appendix III – Calculated Average Power
The Power Threshold for ‘General Population’ portable designation without SAR testing
is: (based on Oct 2005 TCB workshop PPT slide)
(60 / F
GHz
) mW for distances < 2.5 cm
For the 2.4 GHz frequency band, this results in a limit of
25 mW
.
Note that we use the more restrictive “General Population” limit in this case even though the
individuals using this product will certainly be aware of its function and would qualify under the
‘occupational’ category.
Given the maximum transmit duty cycle specified in Appendix II, the average transmitted
power of a WIT2410P remote can be calculated as:
Maximum Pout =
63 mW
(18 dBm nominal)
Maximum Antenna Gain =
6 dBi
(for portable use)
Maximum Transmit Duty cycle (per Appendix II) =
0.0557
Pave (Source-based average) = 0.063 * 4 * 0.0557 =
14 mW
Conclusion:
The WIT2410P Remote meets the MPE limits for a ‘Portable’ device operating in the
‘General Population’.
