    [Eleanor's comment:  This is why we don't "hear" ordinary
    radio and TV signals.]

    Thus the rate of change (the first derivative) of the
    waveform of the pulse is a CRITICAL factor in perception.
    Given a thermodynamic interpretation, it would follow that
    information can be encoded in the energy and "communicated"
    to the "listener".

    Communication has in fact been demonstrated.  A. Guy (Note
    1), a skilled telegrapher, arranged for his father, a retired
    railroad telegrapher, to operate a key, each closure and
    opening of which resulted in a pulse of microwave energy.
    By directing the radiations at his own head, complex mess-
    ages via the Continental Morse Code were readily received
    by Guy.

    Sharp and Grove (note 2) found that appropriate modu-
    lation of microwave energy can result in "wireless" and
    "receiverless" communication of SPEECH.  The recorded by
    voice on tape each of the single-syllable words for digits
    between 1 and 10.  The electrical sine-wave analogs of each
    word were then processed so that each time a sine wave
    crossed ZERO REFERENCE IN THE NEGATIVE DIRECTION, a brief
    pulse of microwave energy was triggered.

    [Eleanor's comment:  This is, in effect a form of what is
    called pulse-RATE modulation.]

    By radiating themselves with these "voice modulated"
    microwaves, Sharp and Grove were READILY able to hear,
    identify, and distinguish among the 9 words.  [Typo?]
    The sounds heard were not unlike those emitted by persons
    with artificial larynxes.

    Communication of more complex words and of sentences was
    not attempted because the averaged densities of energy
    required to transmit longer messages would approach the
    current 10 milliwatts per square centimeter limit of safe
    exposure.

    The capability of communicating directly with a human being
    by "receiverless radio" has obvious potentialities both
    within and without the clinic.  But the hotly debated and
    unresolved question of how much microwave radiation a human
    being can safely be exposed to will probably forestall
    applications within the near future.

    ...
                                    -53-