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The Icom IC-51E PLUS2 but not the American version will emit a 1750Hz tone burst when you push the PTT briefly and then hold it down.
What is this for?
The 1750 tone burst is widely used in European the same way that CTCSS/PL and DCS is used for repeater access in the US. I used tone burst exclusively when living in Germany. Tone burst never caught on in the US.
Required, but never shown