Microwaves!

de KM5FA

One of the two major station improvements this summer gives N5XU microwave gear for the first time. The ball got rolling last spring, at the Belton Hamfest, where Ken KM5FA and Robert KA5WSS pitched in together to purchase a two meter radio. It concluded on a hot July day with all the equipment installed and a successful 1.2 GHz SSB contact with a station over 150 miles away.

What does two meters have to do with microwaves? One way to get transceive capability on a band above 30 MHz is to buy a radio designed specifically to operate on that band; while there are a few ham radios out there that are designed to operate on the 1.2 GHz band, they are somewhat rare, and very expensive. The other common way to get transceive capability on a band like 1.2 GHz is to use a radio designed for another band, such as 144 MHz (which is now refered to as the Intermediate Frequency, or IF, radio) and attach a transverter to it. The transverter converts the transmit signal from 144 MHz up to 1.2 GHz, and converts the received signal from 1.2 GHz down to 144 MHz. A two meter radio, transverter, and all the switching necessary only costs half as much as one of those rare 1.2 GHz transceivers. So, buying a two meter all-mode radio was the first step. The radio we purchased was an original model Yaesu FT-290R, and we got it for just $225.00, a very good price.

The Yaesu FT-290R just before making the first N5XU microwave contact

The next piece of equipment needed was a transverter. Ken KM5FA eventually found one that was suitable, offered for sale by another local weak signal enthusiast. It is a UHF Units transverter that puts out 3 watts on transmit. We also bought a special device from Down East Microwave to interface the two meter radio to the transverter, and an SMA coaxial relay to use for T/R switching after the transverter. Club member George K5TR very generously donated a 45-element 1.2GHz loop yagi on a 12' boom, complete with a bracket for mounting it on the tower.

We decided early on that the best thing to do was to put the transverter and switching devices in a rain-proof box near the top of the tower, and leave the two meter radio in the shack. Why would we want to put all that stuff in a box on the tower? Feedline loss. At 1.2 GHz, signal loss in ordinary coaxial cable, such as RG-213/U, becomes fairly severe. Had we left the transverter in the shack, it would have taken close to 100' of coax to reach the antenna, and our three watt signal would have been attenuated to nearly 300mW by the time it reached the antenna. By mounting the transverter closer to the antenna, the feed line is shortened considerably and most of the power reaches the antenna. Ken KM5FA constructed a frame of light-duty plywood to sit inside the box, and attached all of the components to it.

The UHF Units 1296 MHz transverter in the rain-proof box

Since the transverter and switches all run off 13.8 VDC, somehow power had to be routed up to the box on the tower. The problem with running DC over long distances is that the voltage can drop considerably. There are many schemes for using voltage regulators, voltage-sensing power supplies, and other mechanisms for maintaining constant voltage on the tower. After considerable research into this problem, it was decided that the best thing to do for this project was to use the heaviest guage wire practical. We chose two runs of Romex 12/2 direct burial cable, with the three 12 guage conductors in each run bonded together to increase the surface area. After 85', we saw 13.76 VDC on receive, and 13.60 VDC on transmit, a voltage drop well within acceptable limits.

The first 1.2GHz contact was completed on the evening of 28 July 1999 on 1296.100 CW with John K5IUA in EL29cd, near Houston. It was the first time that all of the components had been hooked up together, even using the same cables that would go on the tower. The loop yagi was literally lashed to the side of the tower with some stiff wire and pointed in John's general direction.

The next weekend, Robert KA5WSS and Ken KM5FA set about mounting the antenna on the mast, mounting the box on the tower, routing the DC power cables to the power supply, and routing the feedline and PTT cable to the two meter IF radio. This was a very hot day, and because we needed to go get some additional parts, most of the tower work was unfortunately done between 3PM and 6PM. Everything was hauled up the tower using a rope and pulley system. Getting the box up to the top of the tower required some extensive bungie cord and lanyard engineering. Surprisingly, dressing the feedline, PTT line, and DC power cables down the side of the tower legs required more time than attaching the antenna and rain-proof box!

The 1296 MHz loop yagi antenna and rain-proof box mounted on the N5XU tower

Feeding the lines through the cable bulkhead took some time, as we needed to drill additional holes. Once through, it took significant time to route everything neatly behind the 19'' equipment rack and around the baseboards to the VHF equipment table. When everything was finally in place, a quick call on 144.200 SSB raised John K5IUA again. After some effort, we made our second 1.2 GHz contact with John, this time on SSB. The installation project started around noon on Saturday, paused for a quick dinner at Thundercloud Subs, and ended around 11PM that evening!