The Microwave Project
Page 4

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Microwave pg. 1
Microwave pg. 2
Microwave pg. 3


Other Sites

Mt. Lemmon
Mount Bigelow
Mule Mountain
Heliograph Peak
Elephant Head
Tucson
Dragoon
Dark Canyon

N7CK and W7IXA
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.

Back of MUX
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 one of the big move was to re-point the Mt. Lemmon dish from Oracle to Mt. Bigelow. (Oracle would have its link still to Pinal Peak) We also moved the origninal SS-2000 radio from Oracle to Mt. Bigelow and hooked it to the interface. green antenna
Antenna on Mt. Bigelow pointing to Mt. Lemmon with 420 link antenna to Jacks Peak in the background.

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.

Downtown rack with test equipmentt
Downtown Tucson Rack
under test

Back of downtown rack

The wiring side of the downtown Tucson rack while under test.
Now we were linked to Elephant Head, Pinal and Mt. Lemmon. Downtown Tucson was still running on the 420 link from Elephant Head. Our solution was to build a whole new Downtown Tucson radio with only a microwave link. We started from scratch building the radio around the microwave link rather than the other way around. It took some time to decide on the controller interface, but other than that things went smoothly thanks to the learning experiences we had on the other sites. Over a period of weeks we built up the rack in KB7RFI's garage and set the levels. The big day finally came and we hauled our precious rack of equipment up the hill. Much to our amazement, the radio worked from the moment we plugged it in and hooked up the antennas. It has needed very little maintenance since. You can see that story in more detail on the Downtown page.

Not much happened for a while as we were preparing for our next link to Heliograph Peak. This link would be the final connection to the Mt. Bigelow hub. We installed another 8' grid dish on the other side of the Mt. Bigelow building in the fall of 2000 as well as mounting the radios in the racks on both Mt. Bigelow and Heliograph Peak. The winter of 2000-2001 was a wet one and the project went on hold until the snow pack on the mountains melted.

During the winter, the interface card cage and cards were completed, so when spring sprung, we headed up the mountain to install dishes. Heliograph got its 6' grid dish installed first as we fought off the hordes of ladybugs on the mountain.
We were pleased with a -54 dBm signal level there and a -51dBm level at Mt. Bigelow (the Heliograph transmitter is 3.75 watts vs 1.7 watts for the Bigelow transmitter.)

While on the peak we also installed the interface, rewired the connections to the controller, changed firmware and set levels. The planned cut-over days were June 15 and 16. We had crews on Heliograph, Mt. Bigelow and Mt. Lemmon.

-51 dBm
-51dBm on
Mt. Bigelow.
To finalize the cutover we had to re-wire the interface at Mt. Bigelow. This involved installing 2 more interface cards into the already crowded interface rack, removing the back and wiring the card sockets and installing jumpers on the existing cards. After fighting the stray RF from all the tv transmitters in the area getting into the test equipment, audio levels were set, a loose connection on Heliograph Peak was fixed and, we were on line with our new link.

Knot of ribbon cable
Bigelow interface

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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