.  Hill Country Research Innovations in Telecommunication and Automation   Turntable   .

This turntable serves as a measurement platform for products, that require an amplitude over angle measurement.  Typical candidates are transmitting and receiving devices as well as reflective elements.  This unit is ideally suited for antenna pattern measurements and for the measurement of Radar Cross Sections (RCS).

It performs equally well with optical measurements to verify beam pattern of LEDs, photocells, photo diodes and lasers.  In the world of acoustics it measures microphones and speakers.
 
 
 

Its construction is very rugged.  The base consists of welded 2''x 2'' steel tubes with mounting holes to secure the unit in a concrete floor.  Two roller bearings support axial and radial load. On top is a 1/4'' solid steel plate with threads. A gear motor interfaces with the hub through a rubber roller.  The motor is driven by a Pulse Width Modulator built into the base of the unit.  A power supply for 5 Volt and 12 Volt is also integrated in the base. The unit requires 110 VAC or 220 VAC but can also run on externally supplied 12 V.  The diameter of the table is 24'' (61 cm). It can accommodate a mechanical load of about one ton.

Turntable with small radar antenna

Two limit switches are provided, one for 0 degrees and one at 180 degrees. The first one interfaces with the software and the user interface to help align the axis of the object to be measured. The second one is hardwired to the motor and stops the unit when the turntable gets to this point. Under normal conditions the software would stop the motor earlier.
 

Front panel controls allows left hand and right hand rotation (regardless of computer command) as well as the angular speed settings.

The turntable control functions interface with the computer via the parallel port. Soft starts and stops (speed ramps) are implemented in the software though PWM algorithms.

For electromagnetic measurements, the systems has a logarithmic receiver that ranges from 100 MHz to 2.5 GHz. An optional frequency converter extends this range to higher microwave frequencies.

This receiver delivers a logarithmitized signal to a data acquisition system and a microcontroller. The microcontroller sends a RS232 data stream to the telemetry transmitter, which beams it to the computer. All this equipment is located on the moving part of the turntable.

A 900 MHz receiver, powered by the serial port of the computer, picks up the signal and feeds it to the serial interface. The software does further processing.

The wireless approach prevents signal cables from wrapping around the turntable.
 
 

The software has an intuitive user interface which makes measurements very easy. The operator only sets the desired angle with the mouse and clicks on the start button.

The turntable turns to the desired angle, turns back twice the angle in opposite direction and finally back to the original position.  While turning back, it measures the radiation pattern of the unit under test.

The measurement data are displayed on the screen as an amplitude over angle function.  Two channels are provides to enable comparative measurements and to evaluate tracking systems like monopuls radar.
 
 

The lower left controls are for semi manual adjustments.  The null indicator lights up, when the turntable is in or passes though the 0 degree position.  A print button is also provided to produce a hard copy of the document. A test number or other info can be entered in the "Test No." data field. When no data are present at the beginning of the measurement, a requester window pops up prompting the operator for action (cancel or continue). The same happens, when there are no data during measurement for more than three seconds.

The horizontal scales of the displays are adjusted automatically to show the desired angle range. Acoustic enrichment is provided by wave files played at major operation points.