    Interference with other sources and receivers is further
    reduced by using directional antennas. The antenna design
    shown is highly directional.

    When penetrating the ground, we wish to eliminate as much of
    the multipath signal as possible. The directional antennas
    reduce the multipath signals detected to those that are
    relatively inline with the wave path, and eliminate much of
    the multipath signal that returns at odd angles.

    Impulse radar uses low power inherently because the
    transmissions occur in pulses separated by periods of no
    transmission. The power of the pulses is offset by the dead
    time between the pulses. The average output of the current
    system is about 300 MICROwatts. THE LOW AVERAGE POWER OF AN
    IMPULSE SYSTEM EFFECTIVELY HIDES THE TRANSMISSIONS FROM
    CONVENTIONAL RECEIVERS.

    Interference can be further reduced in an impulse system by
    using random interval spacing. As long as the transmit and
    receive antennas are in sync, the period between pulses can be
    varied to prevent aliasing with other continuous- or
    pulse-transmission systems that might be operating in the same
    locale. Furthermore, if an impulse system is being used to
    transmit data, varying the intervals between pulses prevents
    other impulse systems from locking onto the signal. Patriot
    Scientific's current GPR system does not use random interval
    spacing.

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