Audiovox FR-230 - Manual (Page 4)

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Your transceiver will achieve its maximum operating range when
communicating with other transciever(s) in a flat open area with
no trees or buildings obstructing its signal. Range may be up to
two miles under such conditions. Obstacles such as buildings,
trees or mountains will tend to reduce the transceiver’s effective
range.
PERFORMANCE
FCC WARNING
Replacement or substitution of transistors, diodes or other parts
of a unique nature, with parts other than those recommended by
the manufacturer, may cause a violation of the technical regulations
of Part 15 of FCC Rules.