[ARC5] Carbon mic pops

[hwhall at compuserve.com]

In this instance, there's only an audio amp and no transmitters to be keyed, so one set of contacts in the T-17 are doing nothing. The other contacts just connect the carbon button to the 10 volt dc "battery" supply. In other words, the mic's line is open until the PTT is pressed. It appears to me that the pop is caused by the dc voltage suddenly appearing on the amplifier grid. I'll post the schematic here later. I don't have it here at the house right now.
 

 Wayne

 

-----Original Message-----
From: Robert Eleazer <releazer at earthlink.net>
To: arc5 <arc5 at mailman.qth.net>
Sent: Tue, Nov 29, 2016 4:16 am
Subject: [ARC5] Carbon mic pops



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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