The idea behind this project was to modify a PMR Radio Walkie-Talkie in that way that it will resend every audio signal which comes to it over a transmission line and vice versa every signal which is received should be provided over a transmission line. Theses transmission lines are connected to my CB Radio station. Doing this will result in a simple, and simplex Gateway from CB to PMR (which is not really legal in my country,.. but hey, things had to be done because i can)
BTW: The President Liberty Mic uses DECT for this technology. This works flawlessly but is limited to about 20m of distance. My versions would work for about 1 km 😈
For the PMR radio devices i used two of my shitty Tevion PMR XL Walkie Talkies. They have a build in RX Led which i used to easily detect the RX Signal. TX was implemented over the build in VOX Function.
Here is the connection scheme:
- TX MIC <-> RX PMR
- RX CB <-> MIC PMR
- TX CB <-> triggered with a Relay which is triggered itself by the RX-LED Signal from the PMR
- TX PMR <-> triggered by the RX Signal from the CB Radio device which triggeres the VOX function of the PMR
The RX Led of the PMR is triggered to ground so i had to build build a Inverter for the Relais. The power supply for the PMR comes directly from the CB Radio Device (over the MIC Connector) over a 5V Power regulator which was built into the PMR.
The whole thing works really good at low costs.
The full schematics for this project is found in the photos below