Introduction

T-22 is a building with two 60 foot dish antennas located on the northern most edge of the mesa north of Boulder, Colorado. The site is part of the current Department of Commerce, Institute for Telecommunication Services (ITS), In 1990 a group of people received permission, from then the National Bureau of Standards, to work on the facility. When we arrived at T-22 it was an abandoned, rat infested building full of racks of vacuum tube equipment. We have made many improvements to the building itself as well as the dishes and control systems.

Building

We started by doing some extensive cleanup and repair of the building to make it a place where humans could work. We then painted the whole interior and erected a wall between the control area and a general work/meeting area. The building could only be easily used in warmer weather since we had no practical way to heat it and prevent pipes from freezing. Water had to be shut off and drained in the winter. We rebuilt the water pump, replaced the hot water heater, installed a propane furnace, replaced the toilet as well as adding heat tape to the pipes to make this a usable building. At first the power bill was paid for by others (I think it was NOAA). When that stopped we found that we could not afford commercial three phase power. We had the power converted to single phase and were able to obtain a 30kw three phase diesel generator from CU that we wired into the towers to run the three phase motors. This was used until we upgraded the motor drive system to a much more efficient single phase variable frequency drive system.

The towers themselves were the object of vandalism in the early years. Each time we installed locks they were broken. We finally ended that by installing very expensive padlocks to the doors of both towers. The scaffold for the lower dish, long gone, was rebuilt to make that dish usable.

Dish drive system

Around 1991 we assessed the drive system and quickly realized that extensive motor repair work was needed before we could even attempt to move the dishes. We undertook the difficult task of detaching and lowering these extremely heavy motors along with their eddy current clutches to the ground so we could work on them. All motors were rebuilt and repaired and reinstalled in working order. The dish gears and elevation screws were inspected and lubricated before movement was attempted. When all of the repairs were completed we successfully moved the upper dish. Early on, most of our efforts were aimed at the upper dish. Only when that was in reasonable shape did we turn our efforts to the lower dish some years later. That is now usable as well.

The original drive systems were not very suitable for tracking celestial objects, or much of anything else or that matter. Eddy current clutches do not provide very precise control over the dish speed and do not allow for slow movement. After several years we were able to obtain two variable frequency drives and appropriate motors. We installed those and were able to make them operate well, within their limitations.

After several years of use we started to have problems with the very large bolts that hold the Azimuth gearbox breaking. This resulted in the azimuth drive shaft breaking. Repairing this was a multi year effort that including custom machining new bolts and a new drive shaft. It has worked well ever since.

Dish RF systems

The dishes had very old, deteriorated Heliax cables and a feed point mount that was difficult to use. We designed a feed point mount that can easily accept different feed point antennas. We also undertook the difficult task of replacing the Heliax. This involved threading this cable up the center of the tower, into the bottom of the dish, attaching it to one of the tripod legs and terminating it at the feed point.

Numerous feed point antennas have been built over the years. Crossed dipoles, horns, helix's and patch antennas have been used at a variety of frequencies.

Projects

We have done several major projects with other groups over the years. The most significant ones were Falcon Gold with the Air force Academy and Paratrak with CU computer science students.

Falcon Gold was the Air force Academy's first student (cadet) designed and built satellite. They realized that they did not have a ground station with sufficient gain to receive the signal from the satellite and came to DSES for help. We provided them with a ground station that tracked the satellite and received its telemetry. This was a multi-month project during which we worked closely with the officers and cadets to help them achieve their goals. It was a great success.

The Paratrak project was a senior project for a group of CU computer science students. DSES built a closed loop controller and provided a software driver for the students to use. They in turn designed the software to drive the dish. The program accepted tracking instructions in several forms including RA and DEC, TLEs ( two line elements) as well as a pull down menu of celestial objects. It was basically a good project but did not provide the accuracy that was required for all of our needs. It is in the process of being replaced with a new system that is currently being designed by an CU aerospace engineering student as a formal project.

We have provided a number of school groups with exciting and educational tours. This has encouraged several of them to pursue physics and engineering when then entered college.