[ARC5] BCB Command Set Purpose

[Mike Morrow]

Andy wrote:

>...it is the only BC-946 I have, and I have been searching for a
>while before I found this one...I don't know how common they are
>in the US, but they seem very uncommon here in the UK.

The broadcast band "command" receivers had as their only real reason
for existance support for the USN ZB/(YE, YG) 246 MHz homing system.

Command    0.52-1.5 MHz   Power          Homing     Homing
Set        Receiver       Adapter        System     Adapter

ARA        CBY/CCT-46145  CBY/CCT-62036  ZB-series  CW/CZR-69076
SCR-274-N  BC-946-B       FT-310-A       AN/ARR-1   R-1/ARR-1
AN/ARC-5   R-24/ARC-5     MX-20/ARC-5    AN/ARR-1   R-1/ARR-1

The power adapter listed above is used to supply power from the BCB
receiver to the homing adapter.  It was always supplied with the BCB
receiver at time of manufacture.  If one finds a BCB receiver today
without the adapter, it's because some hobbyist discarded it.

The USN ZB-series and the JAN AN/ARR-1 are essentially identical.

The homing adapter received a 246 MHz signal that was modulated with
a broadcast band signal.  The broadcast band modulation could be
keyed on and off as a Morse signal, or it could be itself modulated
with an AF voice signal.  The output of the homing adapter was the
broadcast band signal.  The BCB command receivers took this output
of the homing adapter and produced AF Morse output that the pilot
could use to determine bearing to the homing transmitter (typically
an aircraft carrier or a Pacific island airfield) or voice AF ID
information.

This homing system was a pre-WWII US Navy invention that apparently
worked quite well.  It continued in use at least ten years after WWII.
The USAAF made limited use of the system as well, hence the late
addition of the BC-946-B to the SCR-274-N.  The standard SCR-274-N
three-receiver racks had the BC-454-B, BC-453-B, and BC-455-B installed.
If the ZB homing system was to be used, it would be unlikely to be
in an region where the beacon band BC-453-B was necessary.  The BCB
BC-946-B could replace the BC-453-B in the rack, a power cable and a
RF cable could then connect the R-1/ARR-1 to the BC-946-B, and a
MC-415 BCB dial could be installed on the BC-450-A pilot's control box.
That's all that it would take to have a complete ZB homing system on
board.  No AN/ARR-1 control box or antenna switch is required.

But...I have never actually seen any installation information for a
specific aircraft that EVER employed the BC-946-B.  The WWII USAAF
B-29, B-29A, and B-29B flight manuals list the AN/ARR-1, but the
AN/ARN-7 ADF receiver is the set used to process the BCB output of
the AN/ARR-1.

As far as US Navy use of this homing system goes, by middle of WWII
the ZB or AN/ARR-1 was replaced by the AN/ARR-2.  This improved set
combined the whole homing adapter and BCB receiver into one unit that
was installed in the AN/ARC-5 receiver rack, plus made other enhancements.
See the example shown at http://en.wikipedia.org/wiki/File:ARC-5_RCVR.jpg .

The US Navy also entertained the possibility of using the R-24/ARC-5 BCB
receiver as a localizer receiver for the pre-WWII Air-Track ILS system
(ZA, ZA-1, ZAX, AN/ARN-9), though even in that service the beacon band
R-23/ARC-5 would have been more likely.  That's the reason that the audio
adapter MX-19/ARC-5 exists.  However, the Air-Track ILS system was wisely
abandoned by late 1944 in favor of the far superior USAAF SCS-51 (RC-103-A,
AN/ARN-5) ILS (still in worldwide use today).  So even that possible function
for a BCB command set receiver was short-lived.

What remains unanswered is the intended purpose and details of any actual
use of the enigmatic BCB AN/ARC-5 transmitters (T-15, T-16, and T-17/ARC-5).
I wonder if the intended purpose of these mystery transmitters also involved
their use with the BCB R-24/ARC-5.

All that this long-winded write-up leads to is that the BCB command set
receivers were pretty much obsolete for their intended purpose near the
time that they were manufactured. The precentage of BCB receivers that ever
saw any actual military service must be vanishingly small, and must primarily
be ones of the earliest ARA system.  Hence, when these were released, they
nearly all were in NOS condition, unless a hobbyist had worked his magic on
them.

Mike / KK5F