Several users of the AR-300 rotator have found that there is sometimes a difference between the indication and the real azimuth. This is probably causing the gears in the control unit to slip. This one however, the rotator is sufficiently massive and also several times cheaper than other rotators. I had the same problems with one such rotator, so I set out to solve my own display of the azimuth - rotation of the antenna.
The idea is actually very simple - the rotation of the tube from the rotator is transferred via cable transmission to the axis of the potentiometer, which is connected to the branch of the bridge. Voltmeter connected to the bridge is calibrated in degrees 0 to 360.
Let's start by making the sensor. For domestic use, where the rotator is under the roof, an uncovered construction with cable transmission is used. The potentiometer has 100 ohms (other values can be used), linear path. A high-quality potentiometer - aripot - was selected. The transfer is obvious from the photos. It is suitable that the 360° rotation of the antenna represents approximately 2/3 of the potentiometer rotation. This minimizes the inaccuracy in the linearity of the resistance path.
For outdoor or for portable use, the transmission and potentiometer must be built into the rotator chassis, which is more difficult. I recommend grinding a piece of welded wire on the gear in the rotator - this way we get the ability to turn more than 360 degrees and avoid the gear jamming.
Connecting the bridge is simple. To elaborate, I used the Electronic WorkBench program, from which the original schematic is - with a 5V power supply and a 3.6mV output. The sensor is R4. Other trimmers are multi-turn types. With such trimmers it is easier to adjust the range of the bridge, but ordinary trimmers can also be used. Resistors in the middle of the bridge served to reduce the range of the output voltage. The supply cable at the entrance to the cabinet is wound into a choke on ferrite material (3 turns on snap-on ferrite). The bridge has its own power source with a stabilizer that powers the meter bridge.
The greatest freedom is in the way of display. Very handsome the circular display is described on the web OK2KKW. However, it is a bit more complicated to manufacture. Since we are measuring voltage, we can use classic needle gauge, calibrated in degrees. Another possibility is voltmeter with LED, while we set the output from the bridge so that 360° represents 36mV (360mV or 3.6V according to the range of the voltmeter). I originally planned this version, but the local electrical parts stores didn't have this LED voltmeter kit. I therefore used ready-made module LCD voltmeter for 145 Sk. Another option is displaying the azimuth on the computer, e.g. with a simple meter via the COM port.
I mechanically blocked the azimuth display in the rotator control unit. It is no longer necessary and by blocking it we get the possibility of turning more than 360° and avoid difficulties with a dead spot. This is because when it becomes unbalanced, it will move from the north to another place, which can be unpleasant. We will do this by offsetting the gear visible from the underside of the control unit with, for example, a piece of wood.
Calibration requires a little patience. It is convenient to make a "zero" and "three hundred and sixty degree" resistor. It will not be necessary to keep rotating the antenna during calibration. We set the antenna to 0° and use an ohmmeter to determine the resistance of the potentiometer. We then implement this resistance value with a resistor (or by combining several resistors). We will also prepare a second resistor for an angle of 360°.
We replace the potentiometer with a "zero" resistor and balance the bridge - there will be zero on the scale. Now we connect the "three hundred and sixty degree" resistor and use the upper trimmer to set the full deflection on the meter (with a hand meter) or 36.0 on the digital meter display. The elements interact with each other and therefore we repeat the entire procedure until the balance and 360° display are flawless. After calibrating the trimmer, spray paint.
One of the possible versions of the antenna rotation indicator - displaying the azimuth can be seen in the photos. With a digital display with a resolution of one degree, the last digit may jump by a degree or two due to wind.
I have been using the AR-300 rotator for several years and I am satisfied with it despite its shortcomings. It can also handle a smaller KV turn signal provided the upper bearing is used. For about two years he has been spinning a light 3-element directional at 28MHz and is now spinning a 2-element tribander, surviving several strong winds with both antennas unscathed.