My wife runs a horse show once a month. There is an announcer's stand and a judge's stand and the 2 need to communicate with each other constantly all day. Originally there was an intercom system in place that communicated via CAT5 cable. It allowed the secretaries booth, the announcer's stand and the judge's stand to all communicate with each other. This thing required you to push the Talk button and then a 2 digit address (to select the person you wanted to speak with). You were required to push an End button when you were finished speaking. This was too much trouble for the judge and announcer. Then we tried 2 different brands of Walkie-Talkies. One had too much interference no matter what channel you selected and the other just started to intermittently "eat" batteries.
I decided I would try to build a direct intercom between the judge and the announcer using the CAT5 cable already installed. I found some information regarding balanced line drivers here:
How important or is it important for the CAT5 cable to be shielded twisted pairs vs. just twisted pairs? The distance to communicate is approx. 250' (83 meters).
Also, if anyone has links they could post regarding a simple 2 station intercom that operates over CAT5 I would be interested in seeing them. I have searched and it seems all I can find are complicated systems meant for multiple stations. I have also searched for DIY projects but haven't had much luck. I used "audio over ethernet", "audio over CAT5", "CAT5 intercoms", "voice over ethernet", "voice over CAT5" as search terms.