I’m afraid there is some confusion surrounding this subject. Essentially, different comm channels allow one to talk to different people or groups of people. To hear the members of your squadron talking among themselves, for example, you have to have your comm unit set to the right frequency. In a military unit, these channels are encrypted so that the enemy cannot listen in, despite being close enough to pick up the signals; this stops anyone without the proper decryption equipment or information from understanding the communications. During a battle, you generally have communications officers on either side listening for any useful and understandable transmissions, so in order to get the enemy to hear something you want them to hear all you have to do is transmit on an open (unencrypted) frequency. It seems to be that someone can either talk on an open frequency and have people listen passively (like you’re shouting at a crowd with a loudspeaker), or have someone talking back on the other side (like you’re shouting at a crowd on a loudspeaker but another person is shouting back at you). (Continuing the metaphor, talking on an encrypted frequency would then be like you’re shouting at a crowd on a loudspeaker and everyone can hear you, but only your friends can actually understand what you’re saying.) So, if Poe had wanted to, he could have made his transmission and allowed the First Order communications officers to pick it up and relay it to Hux without actually talking to him directly. (But that’s no fun.)
Hope that helps!
~ Jacen