Originally Posted by mm43
I think they are effectively quoting from the TSO C121 spec. The following snippet from their manual would indicate something different:-
It could well be that the spec merely quotes the TSO. It might be that we see only the spec representing what the pingers were once like, without any clue about the present behavior, or the spec might still represent the present design, if little has changed. It is hard to know without more detail. I notice that Benthos has the same spec on their pingers.
Originally Posted by mm43
It appears the 37.5kHz piezo-ceramic transducer looks after itself, and the only requirement is for the 10msec duration switching pulse every second, and that would be derived from a separate time base.
I don't think the excerpt from the manual sheds much light on the question. It still implies that the "signal" (already generated) is applied to the transducer, not that the transducer is part of the oscillator circuit. The former (signal drives transducer) is, in fact, the normal approach to generating pings in underwater transducers. A piezo transducer, coupled to water, has a Q of about 3 to 5, which is not really narrow enough to control the frequency within +/-2.7%, as called for by the spec. Thus there must be one or more time bases to generate the 37.5kHz, 10ms and 1second timing.