User's Manual

Radio Activity S.r.l. 8 / 44
2 Product Safety
2.1 RF Exposure Compliance
FCC Guidelines described in the OET Bulletin 65, state limits for maximum permissible exposure (MPE) and
specify the maximum power density for “General Population/Uncontrolled Exposure”.
This limit is:
• In USA, according to FCC rules, 2 W/m² for VHF band (30-300 MHz);
• In Canada, according to IC rules, 1.291 W/m² for VHF band (30-300 MHz);
• and f/1500 mW/cm² for UHF band (300-1500 MHz).
It implies a constraint in terms of the minimum distance which people must keep from transmitting antenna,
in order to maintain the human exposure under the allowed limit.
With the assumption that a collinear omnidirectional antenna is used with a medium/high gain of 8dBi (=6.3
numeric) and that the transmitter is set at its maximum power (25W, with an additional 20% as possible
effect of tolerance), it is possible to calculate the minimum distance of people from the antenna by using the
following equation for RF power decay in free space (far field):
S = ( P x G / 4 x π r
2
)
where:
S = maximum power density
P = maximum transmitted RF power
G = antenna gain
R = distance from antenna.
This gives:
r =
√
( P x G / S x 4 x π )
For VHF (150-174MHz) equipment the minimum safety distance is r = 2,75 m.
For UHF (407-470MHz) equipment the minimum safety distance is r = 2,36 m.
For 900MHz (806-941MHz) equipment the minimum safety distance is r = 1.67 m.
In particular for the following sub-bands, 406.1-430MHz (by IC and FCC), 450-512MHz (by FCC) 450-470 MHz
(by IC) with the maximum permitted (by IC and FCC) antenna gain of 9.1dBi (see par 4.4.2), the minimum
safety distance is 3.2m up to 470MHz; 3.1m from 470MHz up to 512MHz.
For further information on human RF exposure, contact your local health department. For example, Health
Canada’s Safety Code 6 provides a comprehensive set of guidelines.
For mobile usage, this transmitter must not be co-located or operating in conjunction with any other antenna
or transmitter.