A Squelch Tail is the short burst of white
noise heard on an FM receiver between the time
a signal ceases to be received and the squelch circuit silences the audio output.
This term is often confused with "Hang Time" or "Drop Out Delay" with respect to a repeater.
When you're monitoring a repeater and
the person talking into the repeater un-keys his transmitter,
the short burst of white noise (rushing sound) you hear is the squelch tail from the repeater's receiver.
Then, the repeater's transmitter remains keyed anywhere between 1/2 second and 5 seconds,
in other words it's transmitter <hangs> on before it <drops out>, this is what's known as the hang time or drop out delay.
Some repeaters insert a beep or other type of tone or multiple tones during the hang time.
This tone or tones can be a "courtesy tone" or it can be telemetry signaling that certain links or other devices are connected.
At the end of this time when the repeater's transmitter un-keys, you will hear a squelch tail from your radio's receiver.
When operating simplex with another
station, every time the station(s) transmitting to you un-keys,
you will hear a squelch tail from your receiver.
The purpose of the hang time or drop out
delay on a repeater is to eliminate the repeater's transmitter
from chattering on & off when the repeater's receiver is receiving a noisy, choppy signal.
In the early days of tube type repeaters that used mechanical relays, this saved much wear and tear
on those relays.
Today's solid state repeaters do not have this issue, but a chattering transmitter combined with an already
choppy fluttering signal into a repeater is even more difficult to hear.
Another purpose is for testing purposes.
You can "kerchunk" (key your radio into a repeater) & monitor it's signal level coming back to you.
Always IDENTIFY your station with your callsign when you kerchunk a repeater for testing purposes.
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