Andy Burns  wrote:
> Michael J. Mahon wrote:
>
>> The “Space Command” technology was based not on whistles, but on
resonant
>> aluminum rods at two or four different ultrasonic frequencies, which were
>> struck by spring-actuated hammers when the corresponding button was
>> pressed.
>
> Was that the type susceptible to false triggering by jangling a bunch of
> keys?

Any ultrasonic receiver must be designed to reject typical interference to
operate reliably. The transmitter technology (assuming mechanical
generation of ultrasonic tones) is not a major factor, since both whistles
and chimes both generate strong signals with good frequency stability.

The Space Command system worked serviceably in the marketplace for over two
decades.

--
-michael - NadaNet 3.1 and AppleCrate II:  http://michaeljmahon.com

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