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[Ric Gillespie]

An email from Forum observer David Land in Scotland raises an interesting possibility.

"Re the question of WE 20B coverage of KGMB on 1320 kHz, since the IF frequency is 96 kHz, if the receiver is tuned to 1128 kHz, within its possible Band 2, KGMB would be on the image frequency. There might be an adequate response to hear a signal. (Earlier Tighar analysis of Electra radio equipment.)

However Earhart and / or Noonan would have had to reconnect the transmitter-to-WE 20B link to enable the dorsal antenna. The cable might have been left in-situ when the Hooven equipment was removed.

Night-time sky-wave reception of KGMB at Gardner Island might then have been possible."

I'm not familiar with "image frequency" so I can't comment on that part, but it's true that the dorsal vee antenna could serve dual purpose for transmitting and receiving through terminals on the WE 13C transmitter. We've been assuming that, since the belly wire receiving antenna was lost on takeoff from Lae, any reception of signals from then on (the "A"s on 7500 heard in-flight and any post-loss receptions) were heard via the loop antenna.
Is there any chance Earhart and/or Noonan could have connected the receiver to the dorsal vee? 

First, they would have to know enough to try.
Second, there would have to be a cable and connectors laying around they could use.  It seems to me like the only way that would be possible is if the dorsal vee had, at some point, been connected to the receiver via the transmitter.

That doesn't seem to be the case.  Both the Hooven Radio Compass and the Bendix RDF used a "sense antenna" to resolve the 180° ambiguity. This was a belly wire antenna that ran down the port side of the belly parallel to the belly wire on the starboard side. (See illustration below.)   

 A photo taken in the cabin some time between October 1936 when the Hooven Radio Compass was installed and March 1937 when it was removed, shows no cable connected to the receiver terminal on the transmitter.  So, at least at that time, the dorsal vee was being used only for transmitting.  (see photo)

The lead-in for the starboard-side belly antenna was under the nose directly below the WE20B receiver (see photo).
There was another lead-in aft that appears to be more or less on the centerline between the two belly antennas and under the transmitter, but it's not clear which antenna it's connected to. (see photo)  The starboard antenna lead-in is in the nose, so the aft lead-in must be to the sense antenna. It wouldn't make any sense for the sense antenna to be plugged into the transmitter so there must have been a long cable connecting it to the Hooven, and later Bendix, receiver on top of the fuel tank forward.  The sense antenna and Bendix receiver were not re-installed when the plane was repaired after the Luke Field wreck.  I suppose it's possible the long connecting cable was still in the airplane during the second world flight attempt but it wouldn't be long enough to reach from the WE20B to the receiver terminal on the transmitter. 


NOTE:  The belly antenna illustration below is wrong.  See posting on 4-5-20 for correction.)

[Ric Gillespie]

I'm not familiar with "image frequency" so I can't comment on that part,

But Bob Brandenburg can.

"The WE 20B design precluded the problem David Land raised re image frequency. .

The image frequency is plus or minus twice the intermediate frequency (IF).  If there is insufficient selectivity prior to the input of the receiver mixer stage (where incoming RF signals are converted to the IF), then two signals from stations on frequencies spaced at twice the IF could get through to the subsequent amplifier stages, interfering with each other.  This selectivity problem is avoided in receiver design by including a tuned RF amplifier stage prior to the mixer stage, as was the case with the 20B."

[Harbert William Davenport]

Ric, thanks so much for this post and the very helpful diagram and photos with labels.  The radio gear on the Second Try has for some time been my favorite AE briar patch.
Two queries that may or may not prove relevant:
1. In the diagram of the belly, shouldn’t the position of the Hooven or Bendix DF receiver be shown on the starboard side (not port), and shouldn’t it be a few feet aft of the WE 20B receiver position under the copilot’s seat, to allow for the space occupied by the bulkhead and the R1 tall fuel tank?  This will be relevant to the question you asked, whether the long connecting cable that during the First Try ran from the sense antenna to the DF receiver, IF it was still in the plane during the Second Try, might have been repurposed to run from the transmitter antenna post to the WE 20B receiver under the copilot seat.  That is, can we estimate the minimum length of that long connecting cable?
2.  On the Second Try, what was the location of the cabin entry-point of the lead-in from the dorsal Vee antenna?  Yes, the Hooven-era cabin photo you posted shows it clearly, where it no doubt still was for the First Try in March.  But for the Second Try the dorsal Vee was lengthened and its forward mast moved forward, close enough to where the Hooven dorsal faired loop was located, that it makes me wonder if the lengthened dorsal Vee lead-in might have entered the cabin about where you note the Hooven dorsal antenna in the photo.  But the question here is not so much that cabin entry point, I guess, but whether, once landed on Niku, they could have reached the dorsal Vee antenna from the open hatch over the pilot seat, in order to run a wire directly from the dorsal Vee in to the WE 20B receiver, through the open hatch?

[James Champion]

The transmitters and receivers of the 1930's and most of WWII did not use coax (a controlled impedance transmission line with shield) or any of the special connectors involved. Coax in aircraft radio use really didn't happen until late WWII with radar and IFF transceivers like the BC-645 operating in the VHF/UHF frequencies.

Instead, the lead-in wire for the transmitter or the receiver would have been no more than a well insulated wire without a shield. In the photo you show on the aircraft interior and transmitter,  the antenna connections to the WE transmitter are the white ceramic 'bee-hive' insulators just visible. The connection to these is a push-insert-bare-ware connection that requires no tools. I verified this by finding a picture of the WE 13C on the web.

I didn't find a picture of the antenna connection on the WE 20B receiver, but most likely it's the same type of bare wire connector. Receivers of the era had high-impedance inputs, and a piece of wire was sufficient for quick use. The bigger the antenna, the better.  I've used these old short-wave receivers with no more than the hook of a coat-hanger straightened and poked into the receiver terminal.

Looking at WWII RDF loops (on ebay) they seem to use circular connectors with several pins, probably to connect to the several windings inside the RDF loop for phasing.

So, if Amelia and Fred needed to change around antenna connections at Gardner, all they would have needed is wire, or several lengths of wire, ends twisted together, connecting to the antenna lead-in with no special connections. Wire could have been removed from anywhere in the aircraft wiring if it was not among their spare parts.

[Ric Gillespie]

1. In the diagram of the belly, shouldn’t the position of the Hooven or Bendix DF receiver be shown on the starboard side (not port), and shouldn’t it be a few feet aft of the WE 20B receiver position under the copilot’s seat, to allow for the space occupied by the bulkhead and the R1 tall fuel tank?  This will be relevant to the question you asked, whether the long connecting cable that during the First Try ran from the sense antenna to the DF receiver, IF it was still in the plane during the Second Try, might have been repurposed to run from the transmitter antenna post to the WE 20B receiver under the copilot seat.  That is, can we estimate the minimum length of that long connecting cable?

Thanks Bill.  You're absolutely right.  Corrected illustration below.

2.  On the Second Try, what was the location of the cabin entry-point of the lead-in from the dorsal Vee antenna?

When the mast for the dorsal vee was moved forward by Joe Gurr in Burbank, the lead-in point was moved down on the cabin wall, effectively further lengthening the total antenna length supposedly to give the aircraft some ability to transmit on 500 kHz after the trailing wire was eliminated. All it accomplished was to screw up the other two frequencies.  In Miami, Pan Am was apparently able to improve 3105 and 6210 somewhat by adding a "loading coil" but there was no meaningful propagation on 500 kHz.

  But the question here is not so much that cabin entry point, I guess, but whether, once landed on Niku, they could have reached the dorsal Vee antenna from the open hatch over the pilot seat, in order to run a wire directly from the dorsal Vee in to the WE 20B receiver, through the open hatch?

No problem.  See photo below.

[Ric Gillespie]

Instead, the lead-in wire for the transmitter or the receiver would have been no more than a well insulated wire without a shield. ...

So, if Amelia and Fred needed to change around antenna connections at Gardner, all they would have needed is wire, or several lengths of wire, ends twisted together, connecting to the antenna lead-in with no special connections. Wire could have been removed from anywhere in the aircraft wiring if it was not among their spare parts.

When we first found Artifact 2-2-V-1, there was a length of insulated wire jammed in a tear in the metal.  The NTSB Lab examined the wire and found:
"The wire was a single strand of 0.024 inch diameter copper wire that was 34 inches long. Remnants of what appeared to be degraded and hardened insulation were found randomly along the the length of the wire.  Examinination of a portion of the insulation with the aid of a scanning electron microscope (SEM) revealed fibrous strands, encased in the insulation jacket as denoted by arrow "T" in figure 11B.
Samples of reportedly common aircraft antenna wire labeled "1938" and "1941" were also supplied by the investigator for comparison purposes and displayed in figure 11C.  The "1938" wire sample had a single strand, solid wire core with an easily fragmented inner insulation and a woven fabric outer covering.  EDXA analysis determined that the copper wire core had been tinned prior to being insulated. The inner insulation had two longitudinal fibrous threads, arrowed "T1" in figure 11C, embedded within the insulation material.  The wire small labeled "1941" had a similar outer covering but in contrast had a multiple strand twisted wire core and a rubbery inner insulation with no indications of imbedded threads."

[Ric Gillespie]

Think about this for a second.  If the wire entangled on 2-2-V-1 is, indeed, aircraft antenna wire vintage circa 1938, where did it come from (regardless of whether or not 2-2-V-1 is the patch)?  As a stand-alone artifact it's pretty interesting and potentially extremely important.  Could this hunk of wire be merely garden-variety British electrical wire?

[Bill Mangus]

I suppose it could be but how likely is it something likely of value to the colonists, even if no longer usable as an antenna lead or other electrical use, would be discarded in such a manner, even up to the time the colony was evacuated, that it could become hung up in 2-2-V-1? I guess we'll need to find examples of British wire from the mid-30's to the mid 60's.

(added Monday AM)
It could have come from the Norwich City as well but that would require quite a mixing of debris over the years.

[Randy Conrad]

Ric...in regards to what you guys have been discussing about...I have a question..and it merely relates to the Norwich City. Now, I was never there some 20 years ago when you had your first expedition. But, do you think it was possible if Amelia had the means to use the Norwich City radio if she could. Again, I dont know the status condition of the ship after the fire. I would love to believe that some part of the ship was salvageable. But, it makes me wonder if Fred and Amelia didnt attempt to get on the ship somehow to get access to a better radio, or more batteries.

[Ric Gillespie]

But, do you think it was possible if Amelia had the means to use the Norwich City radio if she could. Again, I dont know the status condition of the ship after the fire.

In 1937 Norwich City was a burned out hulk.  I don't think there is any chance the radio was usable.  Even if it was, Norwich City communicated only in code.  Neither Earhart nor Noonan knew Morse code.

[Ric Gillespie]

When the mast for the dorsal vee was moved forward by Joe Gurr in Burbank, the lead-in point was moved down on the cabin wall, effectively further lengthening the total antenna length supposedly to give the aircraft some ability to transmit on 500 kHz after the trailing wire was eliminated.

Earhart researcher and Forum observer Les Kinney sent me the snapshot below of a May 5, 1937 letter from Joe Gurr to Paul Mantz.
Lots there to digest. Repairs were completed and the airplane was inspected on May 19, so the the letter dates from two weeks earlier. It's Gurr's recommendation about what should be done, not a report of what was actually done.

We also have the following excerpt from a letter Gurr wrote to Fred Goerner in 1970.

"On the take off at Honolulu, with Amelia, Harry Manning and Fred Noonan aboard on their next leg to Howland Island the landing gear folded and the airplane ended up in a ground loop. The damaged plane was shipped back to Lockheed at Burbank for repair. I was called in regarding the radio installation, as everything had to be removed. I took the whole installation home. My job was to make sure that the equipment was not damaged, I took everything apart and checked completely. There were some repairs and adjustments made which I am sure were not required because of the accident, but nothing serious. I worked the transmitter into a dummy antenna and it put out a good signal. While the airplane was being repaired at Lockheed, I took the opportunity to redesign the top antenna. This required a new stub mast on top of the fuselage, behind the cockpit, with a wire to each rudder, and a lead-in from one side to an insulator in the fuselage. The antenna looked similar as before, but now we had about 50% more wire. It made a great deal of difference in radiated energy. Also, because of the added wire, this top antenna now would be more effective on 500KH. I made a loading coil. and tuned it for maximum output. It was still not much under the circumstances but it got out and Amelia was pleased. We designed a belly sensing antenna for preliminary reception of signals to be used for direction finding. I left the reel antenna on board, and it could have been used. Harry Manning knew how to switch it in if necessary. This work was done at Lockheed. However, Captain Harry Manning's leave of absence would now run out before Amelia could make her flight, so he bowed out and returned to Washington."

In his 1970 letter, Gurr says the belly antenna was a sense antenna for the direction finder.  Could the belly antenna be used as both a receiving antenna for voice and a sense antenna for the DF?

[Ric Gillespie]

Could this hunk of wire be merely garden-variety British electrical wire?

Forum observer Dan Cotts writes:

"If that wire is 0.024 inches in diameter then there is no way it could carry
any appreciable amperage. So would not be used in any household electrical
system. Seems to me something like that would be used in communications or
control circuits."

We also have this from Norman Chipps of Chipps Research, an expert in aircraft radio history, in a letter to TIGHAR dated January 31, 1992.

"In most cases the [antenna] wire, until later days, was a heavy rubber and varnished cotton covered small gauge conductor which was very flexible. The fairlead wire (wire inside of the aircraft to connect receivers to antennas ) was a small conductor cable with smaller diameter cloth and rubber covering.
The 22 gauge wire you have found entangled in artifact 2-2-V-1 could possibly be from the external lead or the internal fairlead. Normally electrical lighting wiring and electrical appliance wiring is supported every 6 to 18 inches but the wire you have has no evidence of mounting brackets unless it had been earlier removed by a person in need of a piece of wire or a salvor trying to recover usable items from a wrecked aircraft."

[Ric Gillespie]

Here's a puzzle.
We have two photos that show the front of the 13C transmitter.  In the first photo below, we can see there is nothing attached to the receiver terminal, indicating the dorsal vee is not being used to receive.
In the second photo below, the terminals are hidden behind AE's right leg, but what's the connection at "A" going down through the floor?  Also, what are the features at "B" and "C" that are not present in the previous photo? The date for the photo is unknown but it was taken before the navigator's table was installed.
The third photo was taken March 12, 1937. The navigator's table has been installed (you can see the "goose neck" of the lamp) but features "B" and "C" are no longer present.  Also, the fuel tank vent line manifold "D" has been wrapped with wire(?) and there's a bundle of wire or cable "E" running to either the transmitter or the aft battery.

[Friend Weller]

Feature A appears to not have an insulator but looks more like a cylindrical, push-button connector or a knurled nut/post, both of which I've seen on older radio gear.  Could it be the chassis grounding connection to a welded lug on the keel of the Electra?

[Randy Conrad]

Several days ago I wrote Ron Hashiro of Hawaii an email in regards to an article he wrote on radio history in Hawaii. He wrote me back and it was quite interesting. Thought this might help...

If I may suggest, contacting KSSK radio in Honolulu, which is the successor to KGMB.

Supposedly at the time of Amelia Earhart, KGMB was in the 1300's kHz.  The other station was KGU-AM 760 kHz, which was located in the then Honolulu Advertiser building on Kapiolani Blvd and South Street.  Because the 760 kHz frequency was also used on the West Coat, KGU-AM had to vacate that frequency at night in order to not interfere with the West Coast.

I know the 590 kHz AM tower was on 1710 (?) Ala Wai Blvd, and is since long gone.  The AM facilities have moved to a "new" tower next to Kapalama Canal.  I'm guessing it was the tower on Ala Wai Blvd (it may have been elsewhere) that did the work.  I know up until the 70's, that the RCA 1D transmitter (the one used on the day of Pearl Harbor) was housed there.  The entire building has since been vacated of radio equipment.

additional information...

https://www.qsl.net/ah6rh/am-radio/hawaii/history.html