A repeater has a few basic ingredients – Antenna, duplexer, radio and controller. Any one of those can be a challenge. In this case, two of them turned out to be incredibly easy. I was talking to a local two-way radio guy about my idea, and he said, “I have a VHF lo-band Mastr II you can use.” Just like that, the repeater project had a radio. It had been retired from public service a few years ago, and was just taking up space.
There is a lot to like about GE Mastr II as a repeater radio. Chances are good that your favorite 6m, 2m or 70cm repeater was built with one. Many of them have been retired from commercial use, and are available for little or no money if you do some digging. They have an excellent reputation for clean, stable operation under the 100% duty cycle demands of repeater operation. The power amp (100 watts in this case) has a giant heat sink and can run indefinitely. A very selective front end helps protect against RF and intermod from other nearby transmitters. Modifying a Mastr II commercial unit to operate in the amateur bands is relatively easy; in many cases all it takes is a couple of new crystals and a thorough tuneup.
I don’t have a lot of experience tuning up front ends, nor the test equipment to properly do so. So, I turned to a local ham (who wishes to remain anonymous for now) who has an excellent test bench, and extensive experience with retuning GE Mastr II radios. The Mastr II for this project was delivered to his shack in early February, where he gave it an initial checkout to verify that it is operational, NOT a boat anchor. At the moment, we’re in a holding pattern while we wait for UNYREPCO (the frequency coordinator for this area) to approve a 6 meter frequency. Once we have that, the crystals (one for TX, one for RX) will be ordered.
This same ham also had a spare controller on his shelf that slides right in to an existing slot in the Mastr II backplane, providing all the functionality (CW ID, courtesy beep, hang time, etc.) we need for basic repeater operation! So, we’re all set with the antenna, radio and controller – all virtually free, just a few very minor expenses for parts. The duplexer is quite another story. Stay tuned (pun intended!)