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

Tecom Position Controller

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!!

Azimuth / Elevation Pedestal

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.

Cleaning The Connectors

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.

Dirty Contacts


Pedestal Guts

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.

Synchro Transmitter

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!

Controller Guts

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.

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

  1. George Blake says:

    I used to work for TECOM as a Senior Systems Engineer on these things. I think the pedestal you have is a 203009M???

    It appears pretty clean. The problem you have has nothing to do with the Synchros, limit switches or motors. It is Servo Amplifier settings.

    The Controller is a 203350(A)-2 for 2-axis. The Servo Amplifiers are inside the Controller. They are the black bricks in the rear. The Error you are getting is probably because someone played with the Rate and/or Current Potentiometers on the Servo Amplifiers and it cannot generate enough or is generating too much gain. The software is programmed with a certain velocity. If it cannot go fast enough or too fast, it generates and error. Try timing 180 degrees of travel and calculate the angular velocity. It should be around 12 to 20 degrees per second. It may be as low as 6 degrees per second.

    In NEW condition you are looking at between $80K and $150K. These were used for the Electronic Surveillance community. Some were used for Telemetry Tracking and Satellite, but the majority were designed to be used to move 1-18 GHz Dual LP feeds with parabolic reflectors. They were bought to point at pre-selected locations and listen. The larger TECOM pedestals were used for UAV, Satellite and Telemetry tracking operations. They have to be capable of moving at 20 degrees / second or faster.

    The Reference Gain and Loop Gain are the two main adjustments. Another is TEST OFFSET which Zeroes out the drift. You really need a power supply to set these.
    Find the wire that goes to the REFERENCE input pin and pull it out to access it. DO NOT disconnect its Ground return. Easy enough to find. Ground will go back to Chassis.

    To set the OFFSET you engage the drive and input Zero volts DC. use a DMM to make sure it is Zero. If you see drift with the system ON and the drives engaged, adjust the pot until it stops. Next, SLOWLY adjust the Loop Gain until you can hear the motors buzzing or screaming. Back it off until it stops, then back another 1/4 to 1/2 turn. The Next is done to adjust the Velocity. DO NOT let it go past 120 degrees in either axis. Make sure you have enough travel to let it run. If not, you will hit mechanical stops and break something. If it is close to one of the values I gave you, adjust it so it is closer to exact.

    Do this for BOTH axes. Make sure to re-connect the servo connections for the axes you just adjusted before going to the next one.

    Shut everything off and re-connect everything.

    If it shows the same or worse error, shoot for another velocity.

    My guess is that it is lagging the position and cannot catch up to the end point. You should have an error around 0.05 or less.

    It’s been a while.

    TECOM no longer sells positioners except for maybe one or two they can still harvest from current customers.


  2. superzanti says:

    Is this unit still in use?

  3. Dan EI9FHB says:

    I suggest you should use this to receive video from the International space station. It has just started downlinking video. You need a 1.2M dish and good tracking ,along with the correct feed, preamp and downconverter and satellite card, but it’s the tracking setup that’s probably most of the cost. Search for HAMTV on ISS and there is full specs, or contact me and I can send you on the info. I am researching good quality tracking as most setups are not precise enough. Regards.

    • James says:

      Hi Dan,

      I do plan to use the Az / El rotor for high-precision type work – it is just a matter of getting my ham shack all sorted out at this point. My thoughts were initially with EME work and the occasional satellite contact, however, you present an interesting side-project. I’ve got to get that pedestal out of storage and start playing with it again!


  4. Frank J. Beafore says:

    Thanks James. I mis-sent my address but corrected it here. You realy lucked out with the pedistal and need to get it into action. If you stumble on another, let me know :).

    I have a dream job making special projects for the government. The work takes me into antenna design/build, cool radio projects and UAV’s.

    I even have a Ham Shack in the office.


  5. Frank J. Beafore says:

    Hello – nice web site.

    Do you still have the rotor and controller for sale.


    • James says:

      Hi Frank,

      I’m sorry to say that the antenna positioning system is not actually for sale. The intent of the title was merely to indicate the purchase price of the surplus equipment – suggesting I got it for a steal.

      My hope is to press the Al / El controller & pedestal into service some time this summer for some E-M-E work – so I’ve already got plans for the hardware 🙂 Thanks for your interest though! I hope you find something of your liking soon!


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