[ARC5] BCB Command Set Purpose

[Andy Young]

Mike,
That is a quite fascinating story!
My BC-946-B came without any adaptor. I have a power adaptor, not sure 
whether it is for the SCR-274 or ARC-5 BCB Rx, I'll have to dig it out.
Andy

----- Original Message ----- 
From: "Mike Morrow" <kk5f at earthlink.net>
To: "Andy Young" <andy-young at supanet.com>; <arc5 at mailman.qth.net>
Sent: Sunday, March 27, 2011 5:35 PM
Subject: 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
>