[ARC5] [Milsurplus] Gibson Girl question ( BC-778 ? )

[Bart Lee]

Mike, thanks for this. It will be helpful at the CHRS Museum.  We have two
Gibson Girls.

73 de Bart, K6VK
www.californiahistoricalradio.com
##
-- --
Bart Lee, K6VK, CHRS Archivist and Fellow, AWA Fellow, ARRL Liaison

Texts only to: 415 902 7168

www.bartlee.com

{Bart(dot)Lee(dot)K6VK(at)gmail(dot)com}
<http://www.lawforhams.com/>



On Wed, Jul 19, 2023 at 4:32 AM Mike Morrow <kk5f at earthlink.net> wrote:

> The BC-778-* operates on 500 kHz only.  Here is some general GG
> information.
>
>
>
> The Gibson Girl in US service was actually two different models that
> looked almost identical:
>
>
> 1.  BC-778-*, part of SCR-578-*.  Model with 500 kHz MCW.  1942 and later.
> 2.  T-74/CRT-3.  Model with 500 kHz MCW and 8280 kHz CW.  1945 and later.
>
> The BC-778-* transmitter is a 12A6 LC-controlled 500 kHz oscillator
> grid-modulated by a 12SG7 1000 Hz AF oscillator/amplifier.  It produced a
> nominal 5 watts MCW output when hand cranked at 80 to 100 rpm.
> Instructions say 20 seconds of cranking is required to warm
> indirectly-heated tube cathodes before seeing RF output.
>
>  SOS (. . . - - - . . . sent as one character) is sent six times followed
> by a 20 second dash.
>
> The 20-second dash allows rescue force direction finders to determing
> signal direction.
>
> The GG does NOT send the maritime international 500 kHz distress
> Auto-Alarm signal (12 four-second dashes separated by one second sent in a
> one-minute interval).  Aircraft and naval ships carried no Auto Alarm
> receivers.  It is also unlikely that a hand-cranked keyer would time the
> dashes with sufficient precision to trip an AA receiver's primative decode
> circuitry.
>
> Proper crank speed is indicated by one light bulb and actual RF output by
> another.  Manual keying is possible with a large pushbutton.  Instructions
> warn the operator to send no faster than 5 wpm because of the difficulty of
> sending readable Morse with that pushbutton.
>
> The whole set includes a box kite and two ballons with hydrogen generators
> to lift its 350 foot wire.  On aircraft a 12 foot parachute was attached to
> the storage bag complete with a static line to pull the rip cord after the
> set's bag was pushed out of the aircraft.
>
> Some WWII USAAF ferry flights of large aircraft above the Arctic Circle
> were intended to included the small dry-battery-powered Setchell-Carlson
> Model 591 200-420 kHz receiver (military nomenclature AN/CRR-1) with these
> transmitters to allow the distressed party to receive voice messages from
> rescuers.  The AN/CRR-1 definitely existed.  I have one with manual.  I
> don't know if the AN/CRR-1 was actually used as intended.
>
> Late in WWII the improved T-74/CRT-3 became available.  Mechanically and
> electrically it is almost identical except that when automatic keying is
> selected the six SOS and one 20 second dash are sent for 45 seconds on
> LC-controlled 500 kHz MF MCW followed by 45 seconds on crystal-controlled
> 8280 kHz HF CW.  Manual keying is not possible on 8280 kHz.  After WWII the
> HF frequency was changed to 8364 kHz.
>
>
>
> Mike / KK5F
>
>
>
> -----Original Message-----
> From: howard holden <holden7471 at msn.com>
> Sent: Jul 18, 2023 7:47 PM
>
>
>
> Don’t remember which system the Gibson Girl in the NJ Naval Museum/USS
> Ling had. But, the Gibson Girl is ONLY transmit, and only as long as the
> crank is turning. Should be on 500KC and 8364KC. I guess you could tune the
> 8364KC one to 40M, or the 500KC one to 630M, but they only put out a few
> watts.
>
>
>
>
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