[ARC5] Carbon mic pops

[Robert Eleazer]

I have noted that it is common practice on aircraft now for a PTT to be DPST and to switch both on the transmit relay line (grounds it) and the mike connection itself.  Although carbon mikes are not used much now, I have assumed that preventing such pops was the reason.  The intercom connection, using VOX, is upstream of the PTT.  I suppose another reason for the DPST keying approach is that some radios use the actual mike connection to switch the relay on for the transmitter and do not use a separate PTT line, although I don't think such radios are used on aircraft.  

Wayne
WB5WSV  
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