TACAN stands for Tactical Air Navigation, a system that allows pilots to see the distance and direction to a ground beacon, usually at an airfield or aircraft carrier. This equipment transmits interrogation pulses, receives beacon pulses from the TACAN surface beacon and also prepares the received information for display on the bearing and distance indicators.

The ARN-21 receives in the band 962 to1213 MHz and transmits between 1025 and 1150 MHz on any of 126 switch selectable channels. The uplink is 63 MHz lower for the first 63 channels, or 63 MHz higher for the last 63 channels. TACAN surface beacons are capable of transmitting on 129 channels but the ARN-21 is only capable of operation on 126. All channels have 1 MHz spacing.

ARN-21B equipment had 57.2 failures per 1000 hours of operation. There was a goal to improve upon this figure with the ARN-21C follow-on equipment. The tube count was 73.

AN/ARN-21 principle components. The turret in the electronics box contains 42 crystals. Additional frequency mixing with these crystals produced an additional 84 frequencies.  (Courtesy  Sven H. Dodington)

For a complete technical explanation of  the AN/ARN-21,  please refer to the PDF document written by Sven H. Dodington which appeared in the March 1956 issue of Electrical Communication Magazine.

The AN/APN-21 TACAN DME antenna is the little blade antenna above the tailhook. (s/n 1587) (Photo by Jerry Proc)

Contributors and Credits:

1) http://www.nj7p.org/millist/m4.html
2) Google Books ARN-21
3) Vintage Avionics  https://www.vintageavionics.nl/index.html
4) Sven Dodington article    http://www.coit.es/foro/pub/ficheros/tacan60_ef73f819.pdf
 
 

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Jul 1/21