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Author Topic: Rethinking The Antennas  (Read 21742 times)

Ric Gillespie

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Re: Rethinking The Antennas
« Reply #15 on: April 11, 2020, 07:56:41 AM »

Could it be the chassis grounding connection to a welded lug on the keel of the Electra?

A grounding connection would be my guess.
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James Champion

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Re: Rethinking The Antennas
« Reply #16 on: April 11, 2020, 11:05:41 AM »

The three photos (on the previous page of this thread) show a number of differences.

Photo 1: Lead-in for dorsal antenna is high in the fuselage cabin. In this photo we can see the first stand-off support for the lead in, but it may be a different style standoff from what is in Photo 2. For the antenna, the stand-off supports would have been important as the antenna lead-in has no shielding, and you don't want close nearby metal to affect your antenna coupling and you want to control where the lead-in wire is so it doesn't move about and affect the pre-fixed tuning of the transmitter (i.e. you want to control the parasitic capacitance to ground). Transmitter tuning did not involve maximum signal into the antenna, but minimum signal reflected back into the transmitter. Too much signal reflected back into the transmitter results in heating of the output power tube.

Photo 2: We do not see the lead-in entry. We do see the lead-in as it goes vertical on the sidewall. The lead in is supported by ceramic standoffs (a proper installation practice). In photo 2 we do not see the ends of the 1"x 1" wood supports for the fuel tank crawl-over platform (that should be near the arrow of C and visible in photo 3). So photo 2 may be prior to a crawl over being installed. Does the 'pipe?' in C represent a different fuel-tank vent setup? (I assume those are the tank vent tubes)  Feature A on the WE 13C Transmitter is definitely an antenna ground connection. It can be seen in this photo of another WE 13C.    https://kn4r.com/kn4r/Western_Electric_13-C.html     And the ground connection for the antennas shows up on the schematics.     https://aafradio.org/docs/Western_Electric_WE_13C_Transmitter.pdf

Photo 3: With D it appears that a wire harness is now running along the fuel vent manifold, and tied-down with a wax lacing cord?/wire loom method. As the cable comes to the end of the vent manifold, it goes down the cabin wall - indicated with arrow E. but at E an additional black cable can be seen. Is this the antenna lead-in? That would explain the shielding added to the cable. Shielding the harness would be necessary to keep antenna RF from coupling into the wiring and creating issues elsewhere in the aircraft. Also, the point at where the lead-in exits through the cabin wall cannot be as high as it was in Photo 1, so Photo 1 and photo 3 must have had different antenna arrangements.

Frankly, if I have interpreted photo 3 correctly, the lead-in laced directly to a shielded harness looks to be poor installation practice for this kind of open-wire line. I'm not familiar with acceptable signal and transmission line integrity practices of the 1930's. Close proximity results in a some of your transmitter power shunted somewhere other than the antenna. No doubt that when they did this Photo 3 installation they re-tuned the transmitter output, but that only keeps the transmitter happy.

Since installation manual for a WE 13C Transmitter is not available, I went a aircraft transmitter with similar power output, frequency range, and antenna attachment method. The following is from a installation manual for a military ARC-5 "Command Set" transmitter developed in 1936 and used throughout WWII until the early 1960's. Document: "AN 16-30ARC5-2" Dated Dec 15 1954, Page 9 section 2-6 "Installation" paragraph i. followed by paragraph l.

Quote
i. Short antenna leads inside the fuselage are essential. This requires the use of the minimum, practical spacing between the antenna relay unit, the antenna binding posts on the receivers and transmitters, and the antenna lead-in insulator. Bare wire supported on ceramic insulators, where necessary, should be used for all antenna connections. These installations precautions are necessary to minimize voltage breakdown, to reduce r-f losses, and to keep to a low value the capacitance to ground of the antenna wiring inside the fuselage.

l. To accomplish proper grounding of the transmitters, connect a 'short' flexible lead from the aircraft frame to each of the ground binding posts on the rack. ...... Reduced antenna current from the transmitters will result if these precautions are not observed.

You indicate the NTSB lab reported a wire diameter of 0.024". If a precise measurement (neglectable diameter change from corrosion), then this is the exact nominal diameter of 22.5 AWG wire (0.0240"). This is also 0.61mm. Solid magnet wire is available in 1/2 gauge steps in the present era but what about wire in the 1930's?

I used to play with some of the radios back in the 70's when a teenager and actively experimenting amateur radio ham. Today I work as an electrical engineer (designing power inverters for the aviation General Aviation market) but have done a bit of RF work in my career.
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James Champion

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Re: Rethinking The Antennas
« Reply #17 on: April 11, 2020, 11:30:02 AM »

Here are some items I couldn't figure out about the pictures.

What are the two horizontal 'tubes' running along the wall next to  Amelia's left knee in photo 2? They are at a level higher than the top of the transmitter in that picture. There is nothing at that height in photo 1. Just a different 'tube' at a lower level (about the level of the lower row of fuel tank rivets of photo 1). I seem to recall something in the history of the Electra that the fuel tanks had to be removed for some kind of work - is that correct? Did they re-arrange some of these less accessible items then? Could these be for control cables for something associated with the navigators table? Didn't the Electra have a boot de-icer on the tail early on, and could this be for that system?
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Ric Gillespie

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Re: Rethinking The Antennas
« Reply #18 on: April 11, 2020, 11:59:54 AM »

What are the two horizontal 'tubes' running along the wall next to  Amelia's left knee in photo 2? They are at a level higher than the top of the transmitter in that picture. There is nothing at that height in photo 1. Just a different 'tube' at a lower level (about the level of the lower row of fuel tank rivets of photo 1).

The attached illustration shows how Bill Harney drew the interior of the cabin.  Bill's 25 years of research were exhaustive, drawing on every photo he could find.  He didn't get everything right, but the errors I've found have been minor.
He shows the "tubes" connecting to the auxiliary battery.  He also shows the dorsal vee antenna lead-in in its final position low on the cabin wall.

I seem to recall something in the history of the Electra that the fuel tanks had to be removed for some kind of work - is that correct? 

That's correct but it was in August 1936 shortly after the plane was delivered.

Didn't the Electra have a boot de-icer on the tail early on, and could this be for that system?

De-icing boots were in the original specs but were never installed.
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Ric Gillespie

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Re: Rethinking The Antennas
« Reply #19 on: April 11, 2020, 01:22:55 PM »

The three photos (on the previous page of this thread) show a number of differences.

Photo 1: Lead-in for dorsal antenna is high in the fuselage cabin. In this photo we can see the first stand-off support for the lead in, but it may be a different style standoff from what is in Photo 2. For the antenna, the stand-off supports would have been important as the antenna lead-in has no shielding, and you don't want close nearby metal to affect your antenna coupling and you want to control where the lead-in wire is so it doesn't move about and affect the pre-fixed tuning of the transmitter (i.e. you want to control the parasitic capacitance to ground). Transmitter tuning did not involve maximum signal into the antenna, but minimum signal reflected back into the transmitter. Too much signal reflected back into the transmitter results in heating of the output power tube.

Photo 2: We do not see the lead-in entry. We do see the lead-in as it goes vertical on the sidewall. The lead in is supported by ceramic standoffs (a proper installation practice).

I think we see the same kind of ceramic stand-off in the first photo as we see lower down in the second photo.  I don't think the lead-in has changed between the two photos.


In photo 2 we do not see the ends of the 1"x 1" wood supports for the fuel tank crawl-over platform (that should be near the arrow of C and visible in photo 3). So photo 2 may be prior to a crawl over being installed.

I see what you mean.  Good catch.  So Photo One probably predates Photo Two and they both predate Photo Three.


Does the 'pipe?' in C represent a different fuel-tank vent setup? (I assume those are the tank vent tubes) 

Yes, those are tank vent tubes. so it probably does represent a different vent set-up - a further indication that Photo Two predates Photo One.

Photo 3: With D it appears that a wire harness is now running along the fuel vent manifold, and tied-down with a wax lacing cord?/wire loom method. As the cable comes to the end of the vent manifold, it goes down the cabin wall - indicated with arrow E. but at E an additional black cable can be seen. Is this the antenna lead-in?

I don't know what else it would be.

That would explain the shielding added to the cable. Shielding the harness would be necessary to keep antenna RF from coupling into the wiring and creating issues elsewhere in the aircraft. Also, the point at where the lead-in exits through the cabin wall cannot be as high as it was in Photo 1, so Photo 1 and photo 3 must have had different antenna arrangements.


So it would seem, but a photo of the airplane in the hangar at Wheeler Field in Honolulu on March 18 shows the lead-in entry in the location shown in Photos One and Two, and yet we know Photo Three was taken on March 12.  I can't explain it.

Frankly, if I have interpreted photo 3 correctly, the lead-in laced directly to a shielded harness looks to be poor installation practice for this kind of open-wire line. I'm not familiar with acceptable signal and transmission line integrity practices of the 1930's. Close proximity results in a some of your transmitter power shunted somewhere other than the antenna. No doubt that when they did this Photo 3 installation they re-tuned the transmitter output, but that only keeps the transmitter happy.

The shielded harness was apparently done in early March around the time the Bendix RA-1 receiver was installed.  Is it providing power to the new receiver?  Poor installation practice would be par for the course for the Earhart operation.


You indicate the NTSB lab reported a wire diameter of 0.024". If a precise measurement (neglectable diameter change from corrosion), then this is the exact nominal diameter of 22.5 AWG wire (0.0240"). This is also 0.61mm. Solid magnet wire is available in 1/2 gauge steps in the present era but what about wire in the 1930's?

AWG stands for American Wire Guage -  I looked it up :-)   As confirmed in the NTSB report, the artifact wire and insulation matches 1938 vintage aviation fairlead. 
"The "1938" wire sample had a single strand, solid wire core with an easily fragmented inner insulation and a woven fabric outer covering."  The lead-in we see in the photos of the Electra is encased in a fairly thick rubber covering.  If the artifact wire is fairlead from the Electra, the rubber covering must have come off over the years.
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Ric Gillespie

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Re: Rethinking The Antennas
« Reply #20 on: April 12, 2020, 09:24:45 AM »

The lead-in we see in the photos of the Electra is encased in a fairly thick rubber covering.  If the artifact wire is fairlead from the Electra, the rubber covering must have come off over the years.

The rubber covering on shielded cable we found near the island radio shack in 1996 was originally encased in rubber covering that had become brittle and had mostly fallen off.
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Ric Gillespie

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Re: Rethinking The Antennas
« Reply #21 on: April 12, 2020, 10:52:14 AM »

Here's a new discovery.
The entry-point insulator for the fairlead to the transmitter had been moved down to right beside transmitter before the plane left Burbank.
In Miami, some time between Saturday, May 29 and Monday, May 31, the attach-point of the fairlead to the antenna was moved forward, thus shortening the effective total antenna length.  This was undoubtedly part of Pan Am's efforts to improve the performance of the transmitter.
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Andrew M McKenna

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Re: Rethinking The Antennas
« Reply #22 on: April 12, 2020, 01:38:53 PM »

Ric

If you look at the photo of the aircraft taxiing in Miami "the morning of her take off" it looks to me like both wires are there, one angled forward from the attach insulator, and one angled to the rear.  Is it just my eyes?

See attached and

https://flashbackmiami.com/2016/05/31/june-1st-1937-amelia-earhart-takes-off-from-miami/

Do you have a better resolution copy of this photo?

Andrew
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Harbert William Davenport

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Re: Rethinking The Antennas
« Reply #23 on: April 12, 2020, 05:59:34 PM »

Thanks, Andrew.  For me the Miami_taxiing photo shows up more clearly in the FlashbackMiami link you provided.  There what I see is only the one lead-in attached more forward, in the same position as in the Darwin photo that Ric posted.  So that verifies what we expected, that the change was indeed made in Miami, and during the same time period in which that starboard navigation window was skinned over (and yes, with that patch in Tighar's possession, I have no doubt!).
H. Wm. (Bill) Davenport
3555R Prof of Philos, ret.
 
« Last Edit: April 12, 2020, 06:09:28 PM by Harbert William Davenport »
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Ric Gillespie

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Re: Rethinking The Antennas
« Reply #24 on: April 13, 2020, 08:12:09 AM »

Do you have a better resolution copy of this photo?

Here's a detail from the highest-resolution copy we have.  There's only one wire and it's in the forward location.
You can also see what appear to be two of the rivet lines on the shiny new patch.
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Ric Gillespie

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Re: Rethinking The Antennas
« Reply #25 on: April 13, 2020, 02:02:05 PM »

In Reply #10 in this topic, I attempted to attach a .jpg of a letter from Joe Gurr to Paul Mantz, but it was too big.  Here it is as a .png file.  It should come through okay this time.
Thanks to Bill Davenport for pointing out the error.
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James Champion

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Re: Rethinking The Antennas
« Reply #26 on: April 13, 2020, 06:51:32 PM »

Paul Mantz: 
Quote
Build dural stand for transmitter...

I had to look through several on-line dictionaries to get a non-medical definition of dural. Basically dural is a short form of duralumin.

A change in height would also affect the point at which incoming tides at Gardner would disable the transmitter. Water only has to reach the bottom of the transmitter. It has to reach the top of the aux battery.
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Harbert William Davenport

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Re: Rethinking The Antennas
« Reply #27 on: April 15, 2020, 10:21:34 AM »

Many thanks to James Champion for his very helpful analysis of the three photos in Ric’s Reply #12. 
Let me return our attention to “Photo Two,” the one of AE seated on top of the WE transmitter.
I wish to ask whether we might in this photo be observing a couple of optical illusions --
first, with respect to “Feature C”, and second, as to what AE might be up to, if anything, besides posing for a photo.
   First, I suggest that Feature C in this photo is simply the edge of the “crawl-over platform” that also appears in the other two photos.  The end of the 1”x1” wood support for the platform is not easy to make out, but it’s there, and once you see it, and look at C again as resting on it, you begin to realize that it’s merely an optical illusion that C appears to be a tube connected with the fuel-tank vent tubing adjacent to the cabin wall.  Yes, I could only see it that way at first. 
   My second optical illusion is this:  AE at first appears to be posing a bit oddly, by holding her chin in the palms of her hands.  But look again much more carefully.  Could she rather in this photo be using headphones?  It appears to me that the forefinger of each hand might be pressing to her ear the respective earphone of a headphone set, providing the illusion in the photo of holding her chin.
   If she is using headphones, does that tell us anything useful?  How and why would there be a headphone jack anywhere near that WE transmitter back in the cabin?  That transmitter did not receive, it only transmitted, thus no need for a headphone jack there.  Receivers did provide headphone jacks, but the WE 20B communication receiver was about 15 feet forward in the cockpit, and the DF receiver which we cannot see in this photo, if there, was about half that distance forward.  So why the headphones there in the cabin? 
  Here’s one possible explanation: press reports about preparations for the First Try implied that Manning would be able to do radio work from his position in the cabin. To do that he would have needed to have back there a remote control and a headphone jack, connected at least to the WE 20B receiver, duplicating the ones already in the cockpit.
H. Wm. (Bill) Davenport
3555R Prof of Philos, ret.
 
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Christian Stock

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Re: Rethinking The Antennas
« Reply #28 on: April 15, 2020, 10:30:38 AM »

I don't see headphones. I think she is just posing for the press.
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Ric Gillespie

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Re: Rethinking The Antennas
« Reply #29 on: April 15, 2020, 10:39:10 AM »

   First, I suggest that Feature C in this photo is simply the edge of the “crawl-over platform” that also appears in the other two photos.  The end of the 1”x1” wood support for the platform is not easy to make out, but it’s there, and once you see it, and look at C again as resting on it, you begin to realize that it’s merely an optical illusion that C appears to be a tube connected with the fuel-tank vent tubing adjacent to the cabin wall.  Yes, I could only see it that way at first.

I agree.  Good catch.  There is still the issue of Feature "A". It's not present in either of the other photos and Photo Three definitely post-dates both of the others.  Is "A" something that was added early on but removed before the Hooven installation in October 1936?  Or is it something that was added after the Hooven installation but removed before March 12, 1937 (the date of Photo Three)?

 
   My second optical illusion is this:  AE at first appears to be posing a bit oddly, by holding her chin in the palms of her hands.  But look again much more carefully.  Could she rather in this photo be using headphones? 

The photo below shows what she looked like wearing headphones.
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