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Setting levels on Pinal Peak
Once the meeting was over and we were able to take a breather, we began again by taking a close look at our test equipment. We re-calibrated the frequency selective voltmeters (that we use to measure baseband tone levels) so that they would agree with one another and then made trips to each site to re-set transmitter and receiver baseband audio levels. With the Telettras this involved injecting an audio tone of a known frequency and level and setting the deviation control to null out the first bessel function as viewed on a spectrum analyzer. The level setting became a real learning experience. Once the radio levels were set, we again went to Pinal, Bigelow and Elephant Head and set up the mux cards. We had made homebrew pads and filters to go between the radios and the mux shelves, and we ended up redesigning them 3 times until we had the levels correct.
Early version of the homebrew baseband pad
attached to the back of the mux shelf
At this point, it seemed that we had made no progress, except that we had cut over to our permanent interface equipment. The links were still running from Pinal Peak via Mt. Bigelow to Elephant Head to Downtown and back to Mt. Lemmon. It was now getting time to make some permanent changes. Our next move was a big one. We planned to move the main Palomar controller and the 420 Jack's Peak link radios from Mt. Lemmon to Mt. Bigelow. All that would be left on Mt. Lemmon would be the microwave radio, some interface cards, mux and the 440 radio.
Step two was really the big moving day. We removed the 420 link from Mt. Lemmon to Downtown Tucson, trading the radios to the Pinal group for another set of Telettras. Then we took the Jacks Peak 420 link radios and antenna and the Palomar controller and moved them to Mt. Bigelow, hooking up the remaining 440 radio on Mt. Lemmon to some new homebrew interface cards. After lunch at the Iron Door restaurant (it's great to have a restaurant on your mountaintop) we went to Mt. Bigelow and hooked up the controller and the 420 radio to the mux cards. The only real difficulties we had were in getting the 420 link to work reliably after the move.
Taking advantage of the day, we also changed out the original dish on Mt. Lemmon to a commercial dish with radome. This should help stop the dropouts in bad weather caused by water in the feeds.
All this work completed the system as currently installed. We are planning the next microwave link to Jacks Peak. We have the radios tuned up and are working on the antennas. The radio, mux shelf and interface shelf are already installed on Heliograph Peak.
We have learned that these projects always take longer than planned, but they DO get done. Finally, thanks to all the numerous hams who contributed to the success of this project in so many different ways. Much can be done when we pool our talents.
Keep an eye on this web site for updates and more photos.
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