STC, Standard Cables and Telephones,  the British ITT in Southampton, made its own ARN-21 for the RAF (and Dutch Airforce)

Pictures of all tubes in the British version are in the Virtual Valve Museum


You can download the circuit diagrams here :

ST ARN21  RF circuit

ST ARN21  Video and azimuth circuit

ST ARN21   Modulator and Range circuits

ST ARN21  Power Supply


The standard indicators ID-307 and ID-310, as well as the standard control panels can be used with the STARN21.  There were also British versions, like:


          Type B82   Control,    ref. nr 10L / 2238183  made by  STC,


And two types of  combined Bearing/Range indicators were made by SMITHS  Aircraft instruments:

         Type 9547 indicator   ref. nr.10Q / 16355  which only has four (115V) synchro’s.

           A separate coupler with a lot of synchro’s is needed to convert the tacan

           signals to those for synchro’s. This indicator is shown below.


         Type 9597 indicator has the Range display below centre, and has built-in

           conversion gear  allowing  direct connection to the (ST)ARN-21

A tribute to its inventor, Sven H. Dodington.


British STARN-21

The British decided to make their own AN/ARN21 with all-British components, compatible with the rack mount and cockpit instruments from the ITT-made ARN-21. The British unit, called the STARN21is  made and advertised by STC.     The RAF code was  ARI.1354


There are many differences, to note some:

The STARN21 has 106 tubes, double function tubes ( like double triodes) are not used. The transmitter cavities are gear driven, not by a chain  Therefore, the transmitter is directly behind the front panel, and the modulator  is near the range electronic cards.  The tuning motor is a 400Hz ac motor rather than a dc motor.  Like in the ARN21A, the microswitches are driven by a spiral groove in the turret.

When the range motor must stop, it is left open in the STARN21, rather than shorted as done  in the ARN21.