# Efficient antennas for aviation black boxes

At a frequency of 37.5 kHz a quarter wavelength is about 2 km long. How does the black box efficiently radiate anything if it is not attached to 2 km of antenna?

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The short version of the answer is 37.5KHz is not "radio frequency", it's "audio frequency", so an antenna is not necessary - just a (very loud) speaker, which is basically what the pinger is.