The Microwave Project
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Other Sites

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

It all began in the mid-1970's when the Cactus Radio Club in California came across a large quantity of surplus 2GHz ITT microwave equipment. We had already been experiencing frequency congestion on the UHF band in the heavily populated southern California corridor and we were looking for a way to accomplish two things: a reduction of squelch noises and intermod on the radio links between sites and a way to increase capactiy for more users as the system rapidly grew. The solution was to use the microwave equipment to supply some of these needs. Unfortunately, it wasn't to happen in the '70's. The old varactor diode technology of the radios just proved too unstable to tune to the higher frequency needed by our amateur 2 GHz frequency allocations.
SS-2000 installed on Mt. Lemmon
Meanwhile, there were other projects quietly happening: Troy, WA7ELN, was slowly collecting test equipment and also acquired a few Farinon SS-2000 microwave shelves. These proved
themselves tuneable into the ham bands with some difficulty, but it was possible. Troy managed to get a 1 way link running across the town of Oracle, AZ by the mid-80's. N7CK, meanwhile moved in to the adjacent town of San Manuel. WA7ELN and N7CK got together and decided to build a link for the newly rebuilt Oracle remote in order to tie it into the intertie at Mt. Lemmon. This involved tuning up another set of SS-2000's, re-tuning and building simple antennas and trying to get some sort of MUX and signaling working.
Old mux card
Original homebrew mux card
Our first attempt at MUX was built using a scheme similar to FM broadcast subcarriers. We signaled by putting a high frequency tone on the signal when we wanted the squelch to close.
This would fool the squelch chip in the controller into thinking there was noise and it would shut off.

The system was installed by 1990 and it worked well for our single channel link. The problem was that we wanted multiple links and the other advantages that come with a microwave system. We got lucky and found a source of telco surplus Granger DTL-7300 mux cards around 1992. It was also helpful that most of the cards had E & M signaling tones built in. Our task was both simplified and complicated. We had the cards, but we had to build interfaces to the -24 v signaling levels.

DTL-7300 card

DTL-7300 Card

We built the next link to Pinal Peak, again using another pair of SS-2000's. This time we interfaced the Granger MUX. We learned a lot about level setting and interfacing while building prototype interfaces on the back of the mux card cages.
This link was installed with two channels: one that carried the Mt. Lemmon - Pinal link, passing through Oracle and the other link which terminated at the Oracle controller. This in effect gave us two paths from Pinal to Mt. Lemmon. The system worked for a few years with minor interruptions mostly due to the 'temporary' antennas we used at the Oracle site.

From this point on, we had the basics down and began a search for more modern radio equipment in a quantity sufficient to be able to replace many of our existing 420 links.

The microwave story continues on the
Next Page.

Pinal's link to Oracle
Original Pinal SS-2000 installation

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