[Milsurplus] Spares boxes - ZB. Plus some ZA ILS info.

[Mike Morrow]

Hue wrote:


>The YG and ZB both had spares kits.

That's for sure.  I appreciate the NOS ZB-3 system *with complete spares
box* that I got from you a few months ago.  It looks great with the NOS ARB
sitting under it.  The spares kit has enough stuff to almost re-build a
badly damaged unit.

BTW, has anyone else noticed that many R-1/ARR-1 receivers have
broken/missing insulation material in the first RF assembly?  It makes me
almost think this was deliberately done to de-militarize the unit.

>I happen to think the ARR-1 / ZB, outside of valves, must have been
>very reliable indeed. NO oscillators, basically just a vhf TRF receiver.


I'd say so too.  But I would think it would be a little awkward to use,
except for the fact there was a radio operator to adjust the front end
frequency on the ZB and the demodulating frequency on the RU/ARA/ARB to
place in operation.

I assume that the ZB and JAN AN/ARR-1 units were the main reason for the
existence of the broadcast band ARA, SCR-274-N, and AN/ARC-5 receivers.
The BC-946-B especially was a late addition to the SCR-274-N system, coming
standard with the FT-310-A adapter to power the R-1/ARR-1.  Most AN/ARR-1
units have Signal Corps order numbers on the nomenclature plate.  I wonder
just how much use the USAAF made of this USN homing system.  Since the USAAF
appears not to have adopted any part of the USN's AN/ARC-5, that would make
me think that they also never used the related but significantly improved
AN/ARR-2 receivers to replace the few BC-946-B and R-1/ARR-1 systems that
*may* have been used.

Maintenance manuals for the AN/ARR-2 were being revised and issued well into
1954, and overhauls dates marked on R-4A/ARR-2 are often in the mid-1950s.
It would appear then that the YG/ZB type homing system had a long post-WWII
service career in the USN.  An AN/ARR-2 receiver is shown in almost every
different system described in the AN/ARC-5 LF/MF/HF maintenance manual.  In
my personal AN/ARC-5 setup, I have an R-4A/ARR-2 with an R-26 and R-28/ARC-5
in a three-receiver rack, exactly as depicted in the maintenance manual for
"single-place aircraft."

We don't see much about the USN's ZA instrument landing system.  It worked
with YB ground-based system.  It used a cross-needle glide slope/localizer
indicator that looked like the I-101 ILS indicator used in the USAAF's
SCS-51 ILS.  Technically, the two systems are grossly different.  The ZA was
based on the pre-war commercial 'Air-Track" ILS.  The ZA vertical (glide
slope) needle was controlled by the strength of a tone-modulated signal in
the 90 to 98 mc band.  If the aircraft was too high on approach, the the
signal would be stronger and the needle would drop.  Too low...the needle
would rise.  The pilot thus flew a constant signal strength  approach.  The
glide path for such a signal is approximately parabolic, not linear like the
later Signal Corps ILS.    The horizontal (localizer) needle was controlled
by a combination of tone modulated signals transmitted on LF/MF.  The ZA
used an audio input signal from a LF/MF receiver like the RU-series.  The
R-23 and R-24/ARC-5 (but not the ARA) navigation receivers have a audio tap
in the cathode circuit of the AF output stage that went to a special front
panel adapter (MX-19/ARC-5) designed to connect to a ZA-type of ILS.  I'm
not certain, but I believe that the ZA-type of ILS for which the MX-19 was
intended was the AN/ARN-9.

The USN's ILS was cumbersome and primative compared to the USAAF's SCS-51
ILS.  The USAAF WWII airborne components were the BC-733 localizer receiver
(about 110 mc) and the AN/ARN-5 glide slope receiver (about 330 mc).  The
WWII USAAF ILS technology is identical to that which is still used
internationally today, except for a larger number of RF channels.  Pretty
good for a 60+ year old system.  The "Air-Track"/ZA system quickly became
just a foot-note in the history of avionics.

I'd be interested in hearing from anyone with corrections, history, or more
information on the use of the ZA or ZB systems, or any info about USAAF use
of the USN's ZB-type homing system.

Mike / KK5F