AN/ARN-6 Radio Compass

This is an Automatic Direction Finding receiver, which covers 100 KHz to 1750 KHz in four bands. The equipment can be used a radio compass or other stations can be monitored to obtain weather reports or it may be used as a communications receiver.

A BFO is used with the equipment in Antenna or Loop operation. A fixed frequency of 455.9 KHz is used for band 1 and 143.4 KHz for bands 2, 3, and 4. A tone oscillator is used when the equipment is used in Compass operation mode . The tone oscillator is set for 900 Hz and modulates the CW signal as is passes through the IF stages.

Frequency Range:

Band 1    100- 200 kHz    (IF = 465 KHz)
Band 2    200- 410 kHz    (IF = 142.5 KHz)
Band 3    410- 850 kHz    (IF = 142.5 KHz)
Band 4    850-1750 kHz   (IF = 142.5 KHz)

Power Input: 26.5 VDC at 4.0 amps.
Weight: 60 lb for a complete system.
Receiver Dimensions and Weight: 7 5/16H x 11 3/8W x 15 7/16 D ; 34.75 pounds
Manufacturer:  Bendix or Magnavox Company, Ft Wayne, Indiana, USA.
Circa: 1950

AN/ARN-6 principal components. Mounting MT-273/ARN-6  is an aluminum frame with a built in junction board and a control switch relay at the base. MT-274 is identical to MT-273 except that the control relay is not included. This is the mounting for single remote control applications.  Mounting MT-275 is a rectangular shaped aluminum box with an open top into which the control box mounts. (US Navy pictorial via HNSA) 
Control Box C-149/ARN-6 is a rectangular shaped aluminum box with the necessary circuit elements and controls for complete control of the radio compass unit. That is the unit depicted in the principal components pictorial. C1514/A below, is the control box which lacks the S-meter. There were at least 3 control panels that were a standard cockpit mounting system (a standardized panel system like the 19 inch rack) and one stand alone control box.
C-1514/A rack mount control panel. This was the version of control panel fitted on the Argus.  (Courtesy Google books) 

Another style of control panel made by Gables. Not used in Argus. Shown for reference only.  (Photo by John Mackesy VK3XAO)


Radio Compass unit R101/ARN-6 is contained within an aluminum housing with removable top and bottom covers. It is comprised of the compass circuit, a 16 tube superheterodyne receiver, the automatic loop control circuit and the vibrator power supply unit. Tube lineup: 6 x 12SK7, 1 x 12SY7, 1 x 12SW7, 4 x 12SX7GT, 2 x 26A7GT and 2 x 2050.

The vibrator/transformer power supply  produces AC for the 2050 thyratrons and the autosyn loop position transmission and indication system.

R101/ARN-6 receiver on an MT-273 mount. 
Cover off front view.
Cover off - side view. 
All photos in this table by John Mackesy VK3XAO 

Loop antenna AS313/ARN-6 is an iron core loop which is rotated by a drive motor through a reducing gear train. A compensator, which can be adjusted externally, is used to correct for radio compass deviation error. An autosyn transmitter is geared through the compensator to the rotatable loop and supplies loop position information to the remote indicator system. The entire loop unit is sealed and filled with dry nitrogen. It cannot be opened without special equipment. Electrically speaking, the loop antenna uses a low impedance iron core loop of nine turns, is electrically centre-tapped by means of a shunt coil of 12 turns and electrostatically shielded. It is directional in that the voltage induced in the loop is maximum when the line of travel of the received radio wave lies in the plane of the loop coil . The resultant voltage induced in the loop in the loop is 90 degrees out of phase with the non-directional antenna and leads or lags according to which edge the loop coil is nearer to the signal source.

Sense antenna- The non-directional antenna input circuit of the receiver is designed to operate from a low capacity transmission line connected through the proper matching circuit to a conventional 40 to 1000 picofarad antenna having an effective height of from 0.05 to .5 meter.

Coupling Unit CU-65/ARN-6 provides a female connector for the antenna transmission line and an antenna input terminal.

AS-313/ARN-6 loop antenna without radome. This is a compact servo-operated directional loop aerial sealed into a nitrogen-filled glass-topped housing.  (Antenna photo courtesy BPB Surplus)

AS313/ARN6 in test jig with indicator. (Photo by John Mackesy VK3XAO)


ID-90/ARN-6 is an autosyn driven device which indicates the angular position of the autosyn transmitter located in the loop and gives the bearing of a radio transmitter when the loop is at a true null. It does not have luminescent materials on the pointer and numerals. (3.25 inches square x 5 13/16 inches deep; Weight is 2.1 lbs)

ID-91/ARN-6 is identical to ID90/ARN-6 but it uses luminescent materials on the pointer and numerals. (3.25 inches square x 5 13/16 inches deep; Weight is 2.1 lbs)

ID-92 /ARN-6 is similar to indicator ID90/ARN-6 except that a larger scale is used. The scale is graduated every degree and every 10 degree graduation is indicated by the proper numeral. (3.25 inches square x 5 13/16 inches deep; Weight is 2.1 lbs)

ID231/ARN-6 is identical to indicator ID90/ARN-6 except that the pointer is set at 270 degrees azimuth when the indicator rotor is at its electrical zero position. This indicator is only used in special installations which require the loop to be mounted with its zero heading at 270 degrees.  (5.5 inches square x 6 inches deep; Weight is 3.06 lbs)

This is the ID91B/ARN-6 indicator, one of four types available for the system. (Photo by John Mackesy VK3XAO)

Also available was the dual pointer Type ID-250/ARN
indicator. 3-1/8" size . Made by Bendix Aviation Corp.(Photo by John Mackesy VK3XAO)
The Course Indicator (now called Radio Magnetic Indicator or RMI ) ID-250 has 3 synchro motors. One rotates the compass dial card such that the flight direction is on top, Pointer 1 can be connected to the differential synchro from an ID-307 which then points in the direction of the TACAN beacon. Pointer 2 can point to a VHF OmniRange beacon (VOR) or an automatic direction finder (ADF) through a suitable receiver. This was not fitted in the Argus aircraft.
Item 1 is the ARN-6 radio compass control panel at the Routine Navigator's position. The Argus, did not use the standard ID-91 indicator. Instead it was displayed on the ADF/OPTI instrument as item 2 above. (Photo from Sentinel Magazine, May 1968)
AN 16-30/ARN-6 manual. (Courtesy
Use Back Function to Return To Document

Credits and References:

1)  ARN-6 antenna:  BPB Surplus
2) Ian Snow  RCAF/CF retired.<va3qt-4(at)>
3) John Mackesy VK3XAO  <mack(at)>
4) AN/ARN-6 Summary
5) ARN-6 manual photo
6) ARN-6 info
7) ARN-6 info
8) Tom  Brent <>

Mar 5/10