The KD5SDJ Repeater

Many thanks must first go to Jim Benson, NS5U, for donating the major parts. He supplied the mitrek radio in the base station console and the first three cavities.

The radio that we obtained was being used as a 146.34/94 repeater and already had been modified and had a NHRC-2 controller. It is a Motorola Mitrek VHF high band, 110watt radio. I initially tried to use the repeater as it was with new crystals in the channel elements, but I could not get the squealch circuit or the ptt to work. After studying many different mods published on the internet, and deciding the original technician hadn't exactly used any of them, I decided to undo all previous mods and start over.

Preferring the KISS principle, I chose the easiest mods that seemed to have something in common with the others, and in which I could follow the logic in the schematics.

Carrier detect for the controller is taken from the collector of Q406 on the recieve board. This is fed across a 15K resistor to the base of a 2N3904 on a small circuit board mounted in the frame of the radio console. The 2N3904 is powered from 9.5volts taken off of the time out timer connector. The transistor is being used to give a positive voltage for COS to the controller. All other mods are common ones found in most documentation for duplexing the Mitrek.

The four cavities we ended up with consisted of three made by Decibel Products and one made by Sinclair. All of the cavities are meant for high band VHF, tho it was not easy finding the actual range they would tune. Once I figured out that they would tune down to 124MHz, the tune up was easy. I had to remake the coupling loops for the Sinclair cavity, the originals had N type connectors, one of which was damaged, so I remade them with UHF connectors for consistency. Tuning was accomplished with a MFJ259B for rough in tuning and a HT and modified Micronta signal strength meter.

The repeater ended up on the air alternatively at my house and at Dave's where it is now. It is connected to two super J-pole antennas. The range still isn't great but the antennas aren't very high in the air. On May 12th I delivered to Dave a notch filter courtesy of NS5U again. Hopefully, that will allow us to use just one antenna for transmit and recieve.

More to come as we do more testing and find a permanent location