[ARC5] AN/ARN-9 Air-Track ILS

[Mike Morrow]

Recently I had a small trivia challenge about the filtered audio signal that comes from 12A6 cathode circuit and goes to the front panel adapter of the R-23, R-23A, R-24, and R-148 "navigation" AN/ARC-5 receivers.

I then asked:

> 1.  What function did the navigation receiver provide to the ILS?

It received the LOCALIZER signal that was radiated from the USN Type YC-* Air-Track ILS MF transmitter (300 to 800 kHz).  The YC-* also had a GLIDE SLOPE VHF transmitter (90 to 95 MHz).

> 2.  What is the JAN nomenclature of the adapter panel that connected
      the receiver to the ILS?

Audio adapter MX-19/ARC-5.

> 3.  What is the JAN nomenclature of that ILS?

AN/ARN-9, developed from the earlier Air-Track ILS USN Type ZA, ZA-1, and ZAX.


It's time to answer and provide background for the questions I presented.

The USN in the late 1930s adopted an aircraft ILS that was unlike the ILS that has been in worldwide use for more than 70 years now.

Currently-used ILS is based on the USAAF's late-WWII SCS-51 ILS.  The aircraft part of the SCS-51 consisted of (typically):

VHF LOCALIZER     RC-103-A (BC-732, BC-733) 6 Channels 108-110 MHz
UHF GLIDE SLOPE   AN/ARN-5 (R-89)           3 Channels 332-335 MHz
VHF MARKER BEACON RC-193-A (BC-1333)        1 Channel     75   MHz

The ILS that the USN chose to develop was based on the pre-WWII commercial AIR-TRACK ILS.  This was first implemented with the USN's ZA and ZA-1 ILS which used a MF LOCALIZER receiver (RU-*) and a VHF (90 to 98 MHz) GLIDE SLOPE receiver (ZA).

Main components of the AN/ARN-9 consisted of:
R-43/ARN-9 Glide Slope receiver and Localizer audio converter,
C-62/ARN-9 Control Box
ID-24/ARN-9 Cross-pointer indicator
J-32/ARN-9 Junction Box

Ground equipment consisted of the YC-* MF LOCALIZER and VHF GLIDE SLOPE transmitters.  There was also the YD-* MF MARKER BEACON transmitter (300 to 800 kHz).  The YC-* and YD-* together were designated the YB-*.

The Air-Track ILS was abandoned by the USN in 1944, in favor of the superior and, for the pilot, much easier to use USAAF SCS-51 ILS mentioned above.

Various components of the ZA and ZA-1 can be found, but AN/ARN-9 items except the ID-24 seem non-existent today.  The MX-19/ARC-5 adapter is not too rare.  I think Jack/WA7DIA has assembled a complete ZA.  

Mike / KK5F