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This gives a marked reduction in pulse energy but presumably the bat is temporarily more concerned with the accurate location of one nearby target than with the detection of more distant ones. The pulse also sweeps over a smaller range at lower frequencies, often with the appearance of weak second and even third harmonics that were not previously appreciable. At the end of an interception buzz, the pulses of Myotis may last only 0·25 ms and sweep from 30 kHz to 20 kHz (Fig. 2f). As is shown in the Appendix, these pulses give a more accurate range resolution despite their apparently narrower bandwidth.

This sequence is also produced during the interception of prey, as discussed below, and can readily be elicited by tossing a pebble in the flight path of a hunting bat while listening to it with an ultrasound detector. Through familiarity with this effect, the name 'interception buzz' has come to be applied to the rapid sequence of pulses although strictly it should only be used for the response of the detector as interpreted by the human ear. Even at these very high pulse rates, each pulse is a discrete and beautifully formed frequency modulated sweep but the nature of the pulse changes somewhat.

Secondly, since a pure tone or single frequency is continuous and of infinite duration, a short pulse must be 'less pure' than a longer one and therefore contains a wider range offrequencies. Without going into the details, it is the bandwidth that is important in range discrimination and there are other ways of achieving a wide bandwidth. The actual duration of the pulse only matters if the argument is limited 35 Ultrasonic Communication by Animals to square pulses of constant carrier frequency, as is assumed in many simpler books about radar.

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