Model: RT-21r Category:

Rotator Controller, Remote

From $529.00

The RT-21r is the same as our standard RT-21 except it does not include the large transformer and therefore, cannot directly operate a rotator motor. This unit is intended to control systems that use external relays that in turn operate large motor rotator systems, or to operate our selection of Remote Power Units (RPU).


Additional information

Weight 6 lbs
Dimensions 12 × 12 × 6 in
AC Mains

115 VAC, 230 VAC (no power cable)

R Options

Relay Control 24VDC, Remote Power Unit RPU


None, WiFi (+$116.00)


RT-21 Remote

The RT-21r cannot directly power a rotator motor.  It is intended to interface with external motor control relays (+24VDC) for custom systems where relay control is desired.  The RT-21r is also capable of interfacing to our RPU for control of large motor systems.

  • Relay Control
    • 24VDC relay ouput (recommended)
    • configurable for 12V motor relays, or contact closures
  • RPU
    • Speed control/ramp for DC motors up to 2 HP (90/180V), or 28VDC 16A motors (Prop Pitch)

Control relays or the RPU may be separated from the RT-21r by many hundreds of feet and requires only small guage wiring.  Outdoor CAT 5 cable can be used to minimize cable run costs.  Mounting an RPU or relay panel at the tower is common.


RT-21r Description:

The RT-21r is a universal digital rotator controller that may be user configured for many kinds of custom applications.  We can even configure the RT-21r to directly operate a small 115VAC motor like the older Wilson, or Roto-Brake systems.  Any application where motor current does not need to be supplied by the standard RT-21’s internal 5A transformer.

The RT-21r can be configured for all of the same position indicator variations as the standard controllers.

Why use an RT-21r instead of simple switch control, or modified Hy-Gain boxes?

  • Adds USB and/or RS-232 control
  • Adds high resolution digital display
  • Adds Point & Shoot hands off operation
  • In most cases, improves heading accuracy
  • When used with RPU, adds PWM speed control and gradual start/stop to your system eliminating tower and rotator stresses


RT-21r Features:
  • PWM speed control effective for most rotator types (RPU only)
  • Precision ramp control for smooth starts and stops when used with RPU
  • Manual control using CCW and CW buttons
  • Point and Shoot knob for set and forget operation to 1º precision
  • The ability to correct for mast slippage using OFFSET
  • Computer control via RS-232 or USB to 1/10º  accuracy
  • Precision heading accuracy up to 1/10thº
  • Master/Slave links two or more RT-21 for stacked arrays or turning multiple systems to the same heading
  • Counter-Rotation for single mast systems with rotator above a rotator
  • Fully programmable settings for speed, ramps, brake delay, limits and more
  • Two alternate OFFSETs for offset antenna directions on the same mast
  • Elevation and EME modes optimize for Az/El systems and tracking
  • Limits rotation for side mounts, and allows up to 720º  total rotation for supporting rotators
  • High contrast yellow-green backlit LCD with 8 brightness levels and auto-dim
  • Many built-in safguards to protect your system from over-rotation due to internal or external failures
  • Rugged .080 aluminum chassis
  • Special advanced options for custom applications
  • Supports “Shortest Route” for rotators with more than 360º  rotation capability
  • Comprehensive SETUP Utility software included
  • Free application software for satellite tracking, and remote control and rotator sharing using standard TCP/IP (Internet)


RT-21r Specifications:


  • Approx 4” x 8” x 7” HWD
    (Not including rear terminal strip)
  • Approx 4 lb – Shipping = 6 lb

Input Power

  • 115/230 VAC 50/60 Hz
  • Standard IEC power connector
    and 5x20mm GMA fuse


  • High contrast Yellow-Green backlit FSTN LCD
  • Wight brigtness levels w/auto-dim

Front Panel Controls

  • CCW, CW and CANCEL buttons (Operating)
  • SAVE, CHANGE, SETUP buttons (Setup)
  • Point and Shoot knob (340º = full rotation)

External Relay Control

  • CCW and CW DC relay control (12V or 24VDC relays)
  • various configurations

Operating Modes

  • Normal, Master/Slave, Master/Counter Rotate, Slave/Counter Rotate, Debug, Alt Offset

Position Feedback
Mechanisms Supported

  • Potentiometer 150 Ohm to 10 kOhm
  • Variable resistor 500 Ohm (Others accommodated with minor modification)
  • Proximity/reed switch or Hall effect up to 64 pulses/degree (divide ratio  up to 23,500)
  • 2-Bit rotary relative encoder (special order)
  • Others possible

Position Accuracy

  • Up to 1/3º for potentiometer
  • Up to 1/10º with proximity/reed switch

Brake and Reversal Delays

  • 0 to 6 Seconds

Soft Limits

  • +/- 180º from normal stop
  • Restricts rotation to zero or opens to 720º

Motor Speed Control (PWM)

  • 10% to 100% in 10% steps with 10 selectable start/stop ramp settings (RPU)
  • 100% no ramps  (Relay Control)

Computer Control

  • Compatible with all DCU 1 enabled programs
  • Expanded Ppotocol for GH Tracker and SETUP UTILITY (See manual)


  • User changeable in minutes with no soldering


  • No Motion feedback
  • Pot out-of-range (Pot Systems)
  • Counter Range Error (Pulse counter)
  • Industrial rated Transient Voltage Suppressors on all external terminals

Rear Panel

  • 8 Position barrier strip #6-32
  • Ground stud #6
  • Cable strain relief
  • USB-B
  • DB-9 RS-232


  • Limited warranty, 1 Year parts and labor


RT-21r Set-up Utility:

The RT-21r Setup Utility allows you to manage configuration options and optimize other controller settings from your PC.

It also enables you to . . .

  • Change the vanity boot message
  • See a graphic representation of the rotors rotation range
  • Change the rotors rotation range
  • Modify the security setting
  • Change the NO-MOTION motor timeout
  • Perform Auto-Cal on many rotor types
  • Save rotor settings to files
  • Restore rotor settings from files
  • Test computer rotator control

GH-Setup Utility Chart - Green Heron Engineering

GH Tracker – Satellite Tracking

  • Precision 1/10º automatic control
  • Optimizes your tracking program for the RT-21r
  • Interfaces with WSJT, Nova and others

GH Tracker Satellite tracking - Green Heron Engineering

GH Everyware – IP Networking for your GH Controllers

  • Remotely control your rotators over the Internet
  • Share rotators on your network

GH Everyware IP Networking - Green Heron Engineering


RT-21pp Documents:


Download RT-21r Brochure



Download RT-21 User Manual




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