[Elecraft] [Elecraft_K3] K3, CM-500 oddity, a follow up

[Don Wilhelm]

For those who do not understand the technicalities, I would suggest that 
the CM-500 cannot be plugged directly into the KX3 jack.  The KX3 PTT is 
on the ring connection, and the stock CM-500 connects the Tip and ring 
together for the AF connection.

It MAY work, but it is not a certainty, the KX3 function of the ring 
contact is three-fold - PTT, UP and DWN.
the audio level on the ring may or may not induce one of those functions 
depending on the voltage and current.

It would be better to create a homebrew adapter that would accept the 
CM-500 AF on the tip and ring, and connect that only to the tip of the 
KX3 jack, and at the same time add a small box with a pushbutton for PTT 
and also pushbuttons (with the appropriate resistors) for UP and DWN).

In other words, the stock CM-500 *may* work, but it may not depending on 
the levels presented at the ring connection.

This situation may also be present in microphone designed primarily  for 
computer use - they may be OK, but if they create funny PTT or UP or DWN 
conditions, blame it on the connection between tip and ring on the 
microphone jack.

73,
Don W3FPR

On 3/8/2012 3:46 PM, Joe Subich, W4TV wrote:
>> As for the CM-500, I'd like to know if it is the tip, or ring, on the
>> 1/8 inch plug that is the actual mic audio lead. I will have to try
>> one, or the other, to see.
> The answer is quite simple ... the tip and ring of the CM-500 mic plug
> are connected together.
>
> The supplied battery box has no connection to the ring of the mic
> (3.5mm jack).  Tip of the jack is connected to tip and ring of the
> 3.5mm plug via a 1 uF capacitor.  The positive side of the battery
> (+3.0V) is connected to the tip of the 3.5mm jack with a 2.2K Ohm
> resistor.  The negative side of the battery is connected to sleeve
> (common/ground) of both plug and jack (input/output).
>
> 73,
>
>      ... Joe, W4TV
>
>