[ARC5] Keying Approach

[WA5CAB--- via ARC5]

There is some other reason.  The same circuit (same microphones) is used in 
battery operated sets.  Carbon microphones draw current when operated, and 
if not disconnected during receive periods, would continue to discharge the 
battery supplying them.  This is important in portable and vehicular sets.  
Not so much so in aircraft.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 01/14/2015 15:09:22 PM Central Standard Time, 
releazer at earthlink.net writes: 
> Here is a question about something I have wondered about for some time. 
> From what I have seen, aircraft PTT mikes typically use a DPST and key BOTH 
> the mike line and the PTT line.  In other words, the mike is not connected 
> to the transmitter until the button is pushed that also grounds the tip of 
> the PL-68 and completes the transmit keying circuit as well.
> 
> I am aware that some amateur radio transceivers simply turn the mike on 
> with the PTT switch in series with the mike and that completes the circuit 
> required to cause the transmitter to come on and the receiver to go to 
> standby.  
> 
> Is it possible that the aircraft PTT approach reflects that on some 
> transmitters just connecting the mike to the transmitter is enough to turn on the 
> transmitter or is there some other reason?
> 
> Wayne