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Author Topic: RDF Loop Control  (Read 26661 times)

C.W. Herndon

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RDF Loop Control
« on: July 03, 2012, 12:55:04 PM »

I have been looking at the control box for the RDF Loop Antenna and discovered there are three different ones shown in the Purdue pictures.

First is the one shown in the cockpit. Picture one at bottom.

http://earchives.lib.purdue.edu/u?/earhart,808

Second is the one shown in a picture of AE and E. Jay Quinby of the Western Electric Company. (This one is very similar to the one shown in the cockpit picture.) Picture 2 below.

http://earchives.lib.purdue.edu/u?/earhart,228

Lastly, one in a picture of AE sitting, holding the loop assembly and some "unidentified man" holding a Bendix control unit. The caption for the picture says the man is "probably Harry Manning" but if it is, this is the first picture I have seen of him in which he is wearing glasses. Picture 3 below.

http://earchives.lib.purdue.edu/u?/earhart,913

Very curious. Wonder which one was actually in the aircraft when they left Miami.
Woody (former 3316R)
"the watcher"
 
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Chuck Varney

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Re: RDF Loop Control
« Reply #1 on: July 03, 2012, 03:23:28 PM »

I have been looking at the control box for the RDF Loop Antenna and discovered there are three different ones shown in the Purdue pictures.

Woody,

The first two photos in your attachment are both of the remote control unit for the Western Electric 20B receiver. (Red lines in the attachment to this post indicate how the photographs are oriented relative to one another.)

Your third photo shows Cyril Remmlein holding a Bendix loop antenna coupler. (See my 4 Dec 11 post relating to this.)

Chuck
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C.W. Herndon

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Re: RDF Loop Control
« Reply #2 on: July 03, 2012, 05:25:19 PM »

Thanks for filling me in Chuck. Every day I discover things that are unfamiliar to me even though I thought I had read everything. Way too much to absorb in one reading so I have started over.

The biggest problem I had with the first two pictures was that some of the knobs did not seem to be the same. They still don't but that is not a big deal.

Was the Bendix unit, maybe, what was supposed to give them the ability to "home in" on stations in the higher frequency bands? I noticed that the Bendix unit had a switch labeled "Band" with options for 1, 2, 3, 4, and 5. Do we know if it was still installed when they left Miami?

Who was Cyril Remmien? I tried "Search TIGHAR" and got nothing.

                                                                                                                                                                                                                                                                                                                                                                       
Woody (former 3316R)
"the watcher"
 
« Last Edit: July 03, 2012, 05:29:30 PM by C.W. Herndon »
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Chuck Varney

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Re: RDF Loop Control
« Reply #3 on: July 03, 2012, 08:20:48 PM »

Was the Bendix unit, maybe, what was supposed to give them the ability to "home in" on stations in the higher frequency bands? I noticed that the Bendix unit had a switch labeled "Band" with options for 1, 2, 3, 4, and 5. Do we know if it was still installed when they left Miami?

What "Bendix unit" are you asking about and describing?

Quote
Who was Cyril Remmien? I tried "Search TIGHAR" and got nothing.

Did you search for Cyril “Remmien” instead of Cyril Remmlein? According Amelia Earhart: The Mystery Solved, by Elgin and Marie Long, Cyril D. Remmlein worked in the Radio Research Division of Bendix.  (My identification of him as the gent in your third attachment came from a caption for the same photo appearing in the Long’s book.)

Chuck
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C.W. Herndon

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Re: RDF Loop Control
« Reply #4 on: July 03, 2012, 08:46:54 PM »

Hi Chuck. I was talking about the Bendix Loop Control in the 3rd picture of my first post and shown again here.

Yes, I mispelled the name. I will try again. My eyes are not as good as they used to be especially with the "i" and "l".

Thanks again. Maybe I will get it right this time.
Woody (former 3316R)
"the watcher"
 
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Chuck Varney

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Re: RDF Loop Control
« Reply #5 on: July 04, 2012, 10:11:53 AM »

Hi Chuck. I was talking about the Bendix Loop Control in the 3rd picture of my first post and shown again here.

OK, thanks, Woody.

Quote
Was the Bendix unit, maybe, what was supposed to give them the ability to "home in" on stations in the higher frequency bands?

Well, if there was an ability to home on stations in the “higher frequency bands”—and I interpret those words to mean something in the HF range—and if the only receiver aboard was a general purpose type, then a unit like it was necessary to mate the loop to the receiver.

Quote
Do we know if it was still installed when they left Miami?

No.

Chuck
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C.W. Herndon

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Re: RDF Loop Control
« Reply #6 on: July 04, 2012, 10:34:26 AM »

Chuck, I was just trying to think of some reason why AE apparently thought she could home in on the higher frequencies that she could tune in on her radio receiver. It was obvious, from previous discussions, that learning how to use her RDF was not one of her highest priorities.

Is there any reason to think that the Bendix Loop Coupler might have allowed her to do this if she had known how to properly use the RDF system?
Woody (former 3316R)
"the watcher"
 
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Martin X. Moleski, SJ

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Re: RDF Loop Control
« Reply #7 on: July 04, 2012, 12:33:41 PM »

Chuck, I was just trying to think of some reason why AE apparently thought she could home in on the higher frequencies that she could tune in on her radio receiver.

That, to me, is one of the $64,000 dollar questions.

Unfortunately, I haven't seen an answer to it anywhere.

Note the discrepancies:

June 25th at 2245GMT, the Coast Guard San Francisco office sent a radio message

... Mr. Putnam now at Oakland and advises Ms. Earhart at Bandoeng Java for repairs to motors and departure indefinite.
She will cable details communications from Port Darwin direct San Francisco and you will be given all information immediately. All communications from plane will be on 500, 3105, or 6210 kHz by voice, positions being given at 15 and 45 minutes past the hour. Itasca adjust transmitter for possible use 3105 kHz for voice. Direction finder on plane covers range of about 200 to 1400 kHz.

At 0720GMT, June 26th, Earhart cabled:
 
...Itasca transmit letter A, position, own call letters, as above on half hour at 7.5 MHz. Position ships and our leaving will determine broadcast times specifically. If frequencies mentioned unsuitable night work inform me at Lae. I will give long call by voice 3105 kHz quarter after hour, possible quarter to.
 
This contradicts the June 25th telegram that position reports would be given "given at 15 and 45 minutes past the hour."

Jacobson: "It is unclear why Earhart wants the Itasca to broadcast at 7500 kHz, since she is asking for code and cannot use that frequency for direction finding. The actual wording in the telegram is 7.5 megacycles."

At 1930GMT, June 26th, the San Francisco office of the USCG sent out a priority radio message stating
Following information from Earhart this date quote homing device covers from 200 to 1500 and 2400 to 4800 kHz any frequencies not repeat not near ends of bands suitable unquote. ... assume continuous signals after her direction finder in range. See broadcast on quarter after and quarter before hour on 6210 and 3105 kHz. Am advising Earhart that Itasca will voice radio her on 3105 on hour and half hour as she approaches Howland. ... Advice priority if adjustments Tare ten transmitter satisfactory for use on 3105.

The information on the 25th was that Earhart's DF equipment operated between 200 and 1400 kHz; now two ranges are given: "200 to 1500 and 2400 to 4800 kHz."

Jacobson: "There is no contemporaneous documentation to verify that the information regarding the double frequency band of Earhart's RDF came from Earhart or George Putnam. Based upon the quoted passage, it should be taken at face value and accepted as coming from Earhart."[9] 

The transmission timeline shows that she asked for the letter A to be transmitted on 7500 kcs at 1928.  At 1930, she reports that she heard the transmission, but could not get a null on it.  This is the only transmission she acknowledges hearing from the Itasca.

All I'm doing here is providing background for your question.  Why didn't she understand her equipment?
LTM,

           Marty
           TIGHAR #2359A
 
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C.W. Herndon

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Re: RDF Loop Control
« Reply #8 on: July 04, 2012, 01:06:15 PM »

Chuck, I was just trying to think of some reason why AE apparently thought she could home in on the higher frequencies that she could tune in on her radio receiver.

That, to me, is one of the $64,000 dollar questions.

Unfortunately, I haven't seen an answer to it anywhere.

All I'm doing here is providing background for your question.  Why didn't she understand her equipment?

Marty, thanks for verification of my understanding of her of ability to properly use her equipment and her lack of understanding of its limitations. I was curious as to whether or not someone might have found anything new but didn't much expect it.
Woody (former 3316R)
"the watcher"
 
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Martin X. Moleski, SJ

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Re: RDF Loop Control
« Reply #9 on: July 04, 2012, 02:00:47 PM »

Marty, thanks for verification of my understanding of her of ability to properly use her equipment and her lack of understanding of its limitations. I was curious as to whether or not someone might have found anything new but didn't much expect it.

Barring the discovery of a new cache of documents from someone who gave her advice along the way, I doubt we'll be able to answer the question. 

So far as I can tell, with the materials we have in hand, we have an excellent question that we can't answer.   :(
LTM,

           Marty
           TIGHAR #2359A
 
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Gary LaPook

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Re: RDF Loop Control
« Reply #10 on: July 06, 2012, 02:20:38 AM »

Hi Chuck. I was talking about the Bendix Loop Control in the 3rd picture of my first post and shown again here.

Yes, I mispelled the name. I will try again. My eyes are not as good as they used to be especially with the "i" and "l".

Thanks again. Maybe I will get it right this time.
The reason the control box is so complicated is that it incorporated a way to resolve the 180° ambiguity. This required that you adjust the tuning controls on the control box so that the signal strength of the signals from the loop antenna were exactly as strong as the signals on the sense antenna (the belly antenna?) You can ignore doing this and just deal with the ambiguity the old fashioned way, by using your brain. I asked Brandenburg what would be the indications if the sense antenna were missing and Earhart attempted to use the control box in this fashion, so far, no response. The RDF was not designed to work on 7,500 kcs but, in case if might have worked in a very degraded fashion on this frequency, then Earhart's not knowing how to use the control box and to try it in the ambiguity mode may have been yet an additional reason why she could not get a null.

(I don't know why Bendix introduced this complication because it is child's play to resolve the ambiguity without it. Pilots, who come equipped with brains, have no problem so such circuits are only necessary of ADFs (automatic direction finders, an automatic RDF) because they do not have brains and cannot use external information to resolve he ambiguity.)

gl

gl
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C.W. Herndon

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Re: RDF Loop Control
« Reply #11 on: July 06, 2012, 12:17:30 PM »

Thanks Gary. I had not previously found anything about the function of the Bendix loop coupler. Apparently AE did hear something, a series of dashes if I remember correctly, on 7,500 kcs. Presumedly the signal was picked up either through the loop or, maybe, the sense antenna but once again she "could not get a null". Sounds like a familiar problem.
Woody (former 3316R)
"the watcher"
 
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John Ousterhout

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Re: RDF Loop Control
« Reply #12 on: July 20, 2012, 03:59:07 PM »

(originally from pictures of interest thread)
"...Is this how long the wire runs between the transmitter and box?"
The "wire" seen in the photo runs from the antenna to the antennna controller (in the man's hands in Randy's pictures at the top of this thread).  The Receiver, not the transmitter, connected to the controller, and through it to the antenna.  The loop antenna was only used for receiving.  The controller was mounted on the instrument panel, where it stuck out in a convenient place for Amelia to operate it  (I'll try to find the photo).  The controller rotated the antenna and indicated what direction the antenna was pointing.  It also allowed the number of turns of wire inside the antenna to be selected for best frequency sensitivity.
Correction - a normally reliable source tells me that the controller only provided tuning of the coil, using capacitors, and such.  Rotation must have been by other means, possibly a handle sticking out from the antenna through the cabin roof.  I was confused by the knob in the middle of the control box, thinking it somehow rotated the antenna.
Nice clear view of Amelia's shoe.
Cheers,
JohnO
 
« Last Edit: July 20, 2012, 04:13:03 PM by John Ousterhout »
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Chuck Varney

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Re: RDF Loop Control
« Reply #13 on: July 20, 2012, 08:09:01 PM »

(originally from pictures of interest thread)
 
Correction - a normally reliable source tells me that the controller only provided tuning of the coil, using capacitors, and such.

Your source might also have told you that loop tuning was only one function of the box. As I indicated in comments to the original version of your post, the box is a locally controlled loop coupler, where “locally controlled” means that functions must be selected at the box (not remotely), and “loop coupler” primarily refers to providing means of coupling the loop and sense antennas for unilateral direction finding--but can also refer to coupling the loop antenna to the receiver input.

Quote
Rotation must have been by other means, possibly a handle sticking out from the antenna through the cabin roof.  I was confused by the knob in the middle of the control box, thinking it somehow rotated the antenna.

Zoom this photo and you can see that there’s a hand wheel for turning the loop in Amelia’s left hand and that the knob in the center of the box is marked LOOP TUNING.

Chuck
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John Ousterhout

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Re: RDF Loop Control
« Reply #14 on: July 20, 2012, 09:08:47 PM »

Thanks Chuck - I hadn't noticed that there was a turning knob on the bottom of the loop antenna assembly.  It would have been inside the cockpit, above and to the right of Amelia's head, where her right hand could have easily turned it.  Good observation.
Cheers,
JohnO
 
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