The Digital radios on the 139 can be put into test or Squelch off.
Also, what catches a lot of pilots out is:
If either comm 1/2 recieve channel is off, if it is then reseleced by pressing the transmit select button the radio receive channel is then selected on, but if however the pilot chooses to speak on the other 'Box' and presses the transmit select button for ther other comm the previous channel is then turned back off........ it will only stay selected on if it was previously selected on prior to the transmit channel being selected........
does this make sense?