    Intensity control is accomplished by varying the frequency of the three
    subcarrier oscillators that operate in the 100 to ?00 kHz frequency range.
    A 100 MHz oscillator is turned on and off by the pulse train from the
    subcarrier oscillators.  The duration of this pulse is determined by the
    pulse-duration switch.  These bursts of 100 MHz RF energy are received
    by (2) the receiver-stimulator which is carried ?? the subject, measures
    3.7 cm x 3.0 cm x 1.4 cm, and weighs 20 grams.

    The solid-state circuitry is encapsulated in epoxy resin which provides
    it with very good mechanical strength and makes it waterproof.  Space for
    the ? volt mercury battery is included in the size mentioned above.

    After RF detection, the resulting subcarrier frequency is demodulated into
    an amplitude.  This amplitude controls the current intensity of the
    stimulation pulse by means of a constant current transistor in the output
    circuit of the receiver.  This method makes the pulse intensity independent
    of biological impedance changes over a wide range.  Under average stimu-
    lation conditions, the battery life is approximately one week.

    Operating range is up to 100 feet.

    [EW: This is prototype equipment, unclassified, and operating sometime in
    the 1970s.  Imagine classified equipment at the end of the 20th century!]

    Three channels of stimulation are available.  The pulse intensity of each
    channel can be controlled individually from the transmitter.  The pulse
    duration and repetition rate are the same for all three channels.

    Encephalographic (EEG) Telemetry

    A miniature FM-FM amplfier-transmitter combination and telemetry receiver
    are used for this purpose.  (1) The transmitting circuitry, carried by
    the subject, consists of an EEG amplifier with a gain of 100, input imped-
    ance of 2 megohms, frequency response from 2 to 200 Hz, and a voltage-
    controlled oscillator (VCO) for each channel.  The VCO operates in one of
    the frequency bands assigned for subcarrier oscillators by the IRIG stan-
    dards.

    In these studies, a three-channel system was used which operated on IRIG
    channels (Delgado & Hamlin, 1962; Delgado & Mir, in press; Fonberg and
    Delgado, 1961).  The outputs of all three subcarrier oscillators were
    summed and connected to the single RF transmitter module.

    The miniaturized RF transmitter operates at 216 MHz and it's range is
    50 to 200 feet, depending on the environment.  The size of the three chan-
    nel unit, including the battery, is 4.5 cm x 4.5 cm x 1.5 cm and it weighs
    50 grams.

                                 -132-