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-