Here is a project of a home brew Amateur Radio repeater. A few hams and myself had this stuff laying around and needed to put up a repeater. Greg and I put our heads together and came up with this idea. It is still on version 1.0 and would like to add many features to our next few builds.
As you see in the picture there are many components to a home brew repeater. The radios are Motorola SM50’s. These radios are not recommended for repeaters due to several factors when building a repeater. They are not shielded like other Motorola models. The SM50’s will not work well in high RF’s environments due to the intermod from lack of proper shielding. The preferred model for repeater building is a GM300. Be aware that no radio is 100% duty cycle. We used forced air to cool the heatsink of the radios to help extend the life of the transmit radio. These radios are only temporary until we can obtain som GM300 radios. Some other components are duplexers, power supply, controller (made from an arduino), and misc cable and wiring harnesses.
As for the controller, Greg gets full credit to writing the code for the arduino to perform repeater controller functions. It controls the hang (tail) time and the identifier timing to be compliant with the FCC regulations for proper identification.
The power supply need to be enough to power the transmit radio at full wattage output and all the other load the repeater requires. You need to calculate your full load and add an amp or 2 or 3 to ensure you have meet the amp draw requirements of all your equipment.
The duplexer was tuned by Greg with his spectrum analyzer to notch out and pass the proper frequencies for full duplex repeater operations utilizing a single antenna.
As mentioned before, all the components were laying around at fellow amateur radio club members homes and put together to make a working repeater. So there was very little if none at all to assemble this home brew repeater setup.
The repeater is currently up and running one of the radio clubs repeater locations.
If you would like any further information about the repeater, you may contact Greg or myself.