The 146.76 Mitrek Repeater in Scituate, Rhode Island.
By Peter Harrison AA1PL

Our repeater is on 146.76 in Scituate, Rhode Island. It is owned and maintained by the Rhode Island Amateur FM Repeater Service (RIAFMRS). We operate two 2 meter repeaters, one 220 repeater and one 440 repeater.

Our 146.76 repeater is a wide area repeater. It is located on Chopmist Hill and it covers almost all of Rhode Island, eastern Connecticut, and southeastern & central Massachusetts. We occasionally get reports from southern New Hampshire and Vermont! It is one of the most popular amateur repeaters in southern New England. It is open to all amateurs with no PL required.

Now about the particulars:
We use a single 100 watt Motorola Mitrek transceiver which was converted to full duplex. It is supported by an Astron RS35M power supply, a Wacom BpBr duplexer, some additional surplus bandpass filters in the receive line, an ARR GaAs FET receiver pre-amp, an EMR isolator in the transmit line, a commercial grade Zetron model 37 repeater controller, a Commercial Celwave 5.5 dB gain Super Station Master antenna with 7/8 inch Heliax transmission line. Most of the repeater equipment is neatly rack mounted in a base station cabinet.

The Mitrek's mounting tray is mounted vertically to a 19 inch rack panel. The panel has a cut out behind the PA heatsink. A 4 inch fan is mounted on a 45 degree angle on the backside of the panel to blow cool air across the heatsink. The top cover of the radio is cut out over the PA and another fan blows cool air onto the PA transistors. We also have two 3-inch fans blowing onto the heatsink of the DC power supply. While the radio is capable of generating well over 100 watts of RF power, we have throttled it back to about 75 watts out of the Mitrek. With all of this done, the transmitter runs very cool, even during high use periods where the repeater is keyed up for several hours!

We first built the repeater using a MicroComputer Concepts RC-1000V controller. We had many problems with the controller not keying up the transmitter, keying up but not passing audio, keying up with noise on the audio, losing the voice ID memory, etc. MCC was not very helpful, only telling me that we shouldn't be using a Mitrek Mobile for a  repeater and that it was probably RF related. They finally agreed for us to return it & refund our money. We then bought a commercial grade Zetron model 37 controller and have not had one ounce of problems with it. The repeated audio with the Zetron was significantly improved.

The only other problem we had is with the Astron power supply. While the repeater only draws 20 amps and the PS is rated for 25 amps continuous, after about a year of operation some internal connections started to fail under the high current. The screw down contacts from the regulator board to the big filter cap started to arc & burn up. I beefed the wiring up from the rectifiers to the regulator board/filter cap and to the output connection bolt. I had to solder the regulator board connections instead of relying upon the screw down connections.

I am proud to say that since then we have not had any problems whatsoever. We have never had a problem with the Mitrek transceiver. But we did convert and tune up second identical transceiver to full duplex and it is kept at the repeater site as a back-up. If needed, we only have to unplug the bad Mitrek, plug in the spare one, move the channel elements over to the spare and away we go. The bad one can then be repaired at home at my convenience. I keep a spare control head & cable at home.
Perhaps I am bragging a bit, but if these extra steps are taken,  you will probably end up with a extremely reliable repeater such as ours. (By the way, this is the first and only repeater project I have done).

Peter Harrison, AA1PL
24 Forest Glen Drive
Hope Valley, RI 02832