Model: RT-21D Category:

Rotator Controller, RT-21D


RT-21D Rotator Controller, Deluxe

The RT-21D is the deluxe version of the RT-21.  Same features, same options except:

  • Upgraded High Intensity blue OLED display w/auto screen-saver
  • Higher resolution Point and Shoot Knob
  • All black chassis, front overlay w/white lettering

Additional information

Weight 11 lbs
Dimensions 12 × 12 × 6 in



The RT-21 is our standard controller for most applications.   Supports all currently available commercial amateur rotators and can be configured to work with virtually any rotator ever built.  Comes standard with:

  • Off-white chassis and front overlay, black cover
  • Bright LCD with variable intensity yellow-green backlight.
  • Front panel CCW and CW controls, Point-and-Shoot knob, and computer control


RT-21 Standard Description:

The RT-21 is a universal digital rotator controller that can be user configured for motor voltage and position feedback. Configuration is accomplished by a combination of PCB jumpers and software settings, no soldering or major disassembly is required. This flexibility allows the RT-21 to operate any commercial amateur rotator being built today, and virtually any rotator ever built. In addition, there are configuration settings that allow custom control for commercial and industrial systems.

The RT-21 is a universal digital rotator controller that can be user configured for motor voltage and position feedback.  Configuration is accomplished by a combination of PCB jumpers and software settings, no soldering or major disassembly is required.  This flexibility allows the RT-21 to operate any commercial amateur rotator being built today, and virtually any rotator ever built.  In addition, there are configuration settings that allow custom control for commercial and industrial systems.

Why upgrade your controller?

In addition to simply running your rotator or changing to meet your future rotators, the addition of an RT-21 will add modern functionality to your rotator:

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

The RT-21 manual contains separate pages detailing the setup, hookup and calibration of 14 of the most common rotators in use.  Additional resources are available from Green Heron in the form of applications notes, that detail less common or custom requirements.  In addition, we have developed experience and have documentation on many older rotators and custom requirements.

Common Rotators Supported and Documented in the Manual:

  • Hy-gain HAM series, T2X and HDR-300
  • Create RC5 series
  • Yaesu All models
  • Orion 2800 and 2300 models
  • TIC RingRotor
  • Prosistel
  • Alfa-Spid
  • Alliance HD-73
  • Rotor Doctor (CATS)
  • Diawa MR-750/MR-300


  • PWM speed control effective for most rotator types
  • Precision ramp control for smooth starts and stops
  • 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 2 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 houses CCS rated power components and 5 lb transformer
  • 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-21 pecifications:


  • Approx 4” x 8” x 7” HWD
    (Not including rear terminal strip)
  • Approx 8 lb – Shipping = 11 lb

Input Power

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


  • High contrast Yellow-Green backlit FSTN LCD
  • Eight brightness 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)

Motor Power
(Selectable voltages @ 5A)

  • 18 to 36 VAC
  • 12 to 48 VDC
  • 115VAC (call)

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

Selectable Options
(specific Rotator Settings)

  • POT, Counter, HAMx, T2X, Orion,

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
  • 100% no ramps

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 (TIC-PST Option)
  • Counter Range Error (Orion, SPID, 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-21 Set-up Utility:

The RT-21 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-21
  • 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-21 Documents:

Download RT-21 Brochure

Download RT-21 User Manual


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