[ARC5] BCB Command Set Purpose

Sun Mar 27 21:21:44 EDT 2011

Mike,
Tnx for all your info on the BC-946. You said that they pretty obsolesce early on in the war. Interesting thing I ran up with a BC-453 that was "RANGE MOD" 25_NOV_53  MWO 623G05   The range mod put it on the bcb. Why do you thing they would bother if it we outmoded for navigation?
Terry

-----Original Message-----
From: Mike Morrow <kk5f at earthlink.net>
To: Andy Young <andy-young at supanet.com>; arc5 at mailman.qth.net
Sent: Sun, Mar 27, 2011 12:35 pm
Subject: [ARC5] BCB Command Set Purpose

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

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