[Milsurplus] ARN-6 vs ARN-7

Mike Morrow kk5f at earthlink.net
Thu Jul 31 13:08:22 EDT 2008


>Looks ARN-6 later than ARN-7.

Generally, for most (but definitely not all) JAN-nomenclatured items, the component number is a better indication of chronological order than the system number.  The receiver component of the AN/ARN-7 is R-5/ARN-7, and for the AN/ARN-6 it is R-101/ARN-6.  That's a good (and in this case accurate) indication that the AN/ARN-6 is more modern than the AN/ARN-7.

As Robert stated, the AN/ARN-7 is the JAN nomenclature for a very modestly improved SCR-269.  I believe this improved ADF was to have been called the SCR-639, but that changed under the new JAN system to the AN/ARN-7 instead.  The only substantive change from the SCR-269 was adding a fourth band for coverage of 100 to 200 kHz, and adding a CW-MCW switch on the remote control box (C-4/ARN-7).  Everything else is the same as the SCR-269, though I've read that there was a LP-31 loop that could be used in place of the SCR-269 LP-21 loop.  I don't know what the difference is between the LP-21 and the LP-31...maybe the LP-31 better supports the added LF band. 

The AN/ARN-6 is more modern and much lighter in weight than the AN/ARN-7.  Plus, only 28 vdc is required for the whole system, unlike the AN/ARN-7 that needs 400 Hz 115 vac and 28 vdc power.

>Like ARC-1 vs ARC-4.

That's a quirk, because both parts of the RT-18/ARC-1 name would incorrectly imply that it was earlier than the RT-19/ARC-4.  I suspect that occurred when the JAN name for the AN/ARC-4 was applied long after the set was first adopted as the commercial W.E. model 233.

>ARN-6 lasted all the way thru F-100

And long after that...I've seen AN/ARN-6 installations still in service in a number of older USN and USAF aircraft in the 1970s.

>ARN-6 guts show Bendix MN-26 heritage as does ARN-7

Fans of RDF/ADF development should look at the odd duck of the SCR-269 series, the Fairchild Aviation SCR-269-F.  Mechanically it's somewhat different, and electrically it's *very* different from any of the Bendix-based other versions of the SCR-269.  The BC-433-F receiver can be interchanged as a whole unit with other BC-433s, but very few of the internal components can.  That must have complicated the spare parts supply chain and the life of the radio technicians.

The USAAC/USAAF had the world's most modern airborne DF sets from the mid-1930s on.  The SCR-242 (BC-310) RDF from 1936 is amazingly modern, especially in comparison to the USN's awkward late-1930s DZ-series of RDFs.  IMO, one sees little DZ set use in WWII USN aircraft because the USN had the good sense to use the USAAF's superior SCR-269 instead.

Mike / KK5F


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