[Elecraft] [KX3] Small Problem or Finger Trouble?

[Don Wilhelm]

Gary,

Not "finger trouble", but just the way logic circuits work.
There is a pullup resistor on the ACC2 IO PTT input - which makes it 
high unless one takes measures to short it to ground.

If you select Hi=PTT with nothing (or nothing active low) into the ACC2 
jack, PTT will be asserted by virtue of the pullup resistor.

Normal operation for most PTT switches is to provide a path to ground 
(logic Low) when the switch is closed and an open circuit when the 
switch is open.  In order to provide a logic high level when the switch 
is open, the pullup resistor is necessary.

So bottom line, the PTT input is normally at +5 volts.  If you have 
nothing in the ACC2 jack that creates a short between PTT and ground, 
the level will be High - so setting the ACC2 PTT menu to Hi will 
activate PTT.  Normal PTT is for a low (short to ground) when PTT is 
active, but there are other schemes that may require PTT=Hi although 
they are not as common.

73,
Don W3FPR

On 4/19/2014 7:19 PM, Gary Hawkins wrote:
> I was setting up my KX3 for a headset and external PTT connected via 
> ACC2 today.  As I was setting the correct mic bias and PTT setting I 
> noticed that if you set ACC2 IO Hi=Ptt the audio output is cut off. 
> The radio does not seem to be transmitting but there was no audio. 
> Other ACC2 IO settings act as expected.  Is is a small problem or just 
> finger trouble?