Tecom Az / El Antenna Rotor (and Controller) for $80

I’ve been browsing the PWGSC Crown Assets website for a few days looking for a spectrum analyzer or more modern oscilloscope to enhance my electronics tool-chest.  Nothing terribly interesting had been coming up until very recently. I saw a listing for a: “Tecom controller” which caught my eye. I often look for inexpensive things to take apart to see what makes them tick, and this piece looked promising. When I looked into the auction a little bit more, I realized that the auction picture was for a azimuth / elevation controller. Further poking around showed what I thought was just a heavy-duty elevation rotor.

Initially, I posted a bid of $40 thinking “That would be cool to take apart”. After a bit more consideration, I thought, “aww heck, why not drop $80 and hope for the best?”. Well, the auction closed yesterday evening and the items were mine (after prompt payment of course)! I acquired this amazing piece of kit for roughly 20dB less than it is worth!!

While waiting for the auction to expire, I did some poking around to see what I could learn about the antenna controller / azimuth & elevation pedestal. Turns out that what I bought is a Tecom MIL-SPEC system most often used for tactical communications. There isn’t a whole lot of information available on the equipment, which is par for the course with equipment like this. When I picked the unit up, I was shocked / impressed with the mass and build quality of the pedestal. The darn thing weighs nearly 100lbs! I’m still trying to find the specs on the drive assembly but a cursory search suggests that the unit will accommodate at least 100lb of antenna.

After getting the units home, I had to connect everything and play! Testing the unit revealed that it is accurate to 0.1° in both the elevation and azimuth axes. Using the “PNT” button, I had the drive mechanism point to 90° & 90° which showed a systematic error of 1.3° when moving counter-clockwise.

I figured that the position reporting system was likely a potentiometer of some design, coupled to the motor output shaft to give a real-time indication of position for the controller. Often times, old, corroded connectors can play havoc with the resistance of a signal path, and this could have been the cause of the 1.3° error. I used some spec.-grade isopropyl alcohol to clean the myriad of pins in the connectors, resulting in plenty of gunge on q-tips.

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After reconnecting the cables, I tested the temperamental azimuth mechanism and it still stalled out when going counter-clockwise. The same recurring 1.3° error was present when traversing counter-clockwise. The elevation control is flawless, always parking no more than 0.1° away from the instructed position. I had to crack the controller and the pedestal open in order to ascertain whether I can set the “zero point” or not. As it turns out, I did not see any potentiometer labeled for such a purpose.

On the right side, you can see a potentiometer on the bottom and a synchro control transmitter above it. As it turns out, it is the synchro control transmitter which reports the positional data back to the controller. I’ve tried making small adjustments in the mounting to correct for the 1.3° error which temporarily solved my problem. Once the pedestal was instructed to traverse from CW to CCW again, the 1.3° error was back! Drat!

I’ve requested quotes from various military supply houses to feel-out the replacement cost, and well, as you can expect with MIL-SPEC stuff, it looks VERY expensive. Put it this way, a brand-new Yaesu G-5500 would cost less. I’ve pulled the synchro out to see if I could reproduce the problem by checking for back-lash issues. No luck. I’ve tried increasing the tension in the anti-backlash gears to see if that would solve the problem. Still no luck. Sadly, it would seem that the synchro may be the root cause of the problem.

In either case, the unit is still accurate to ±1.3° which is actually fantastic! The controller can be programmed to scan a sector (elevation or azimuth), seeking out weak signals. Using a serial port, the controller can also be put into a remote mode, allowing for computer control (like most low-rent az/el controllers).

I’ve posted a video to YouTube to demonstrate the az / el pedestal drive mechanism.