NR16020 antennas

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The design and function of the trailing antenna and loop antenna are discussed separately. This article is concerned primarily with the question of the location and function of the other antennas.

There are many kinds of antennas in this discussion:

  • Dorsal antenna: a Vee mounted on the top side of the aircraft.
  • Ventral antenna: a straight wire mounted on the underside of the aircraft.
  • Loop antenna: interior or exterior direction finding loop.
  • Trailing wire antenna: exited from the tail or from the underside of the plane.

Bell Labs installation: dorsal Vee

Length of dorsal antenna

"The high-frequency antenna installed aboard the Electra in March 1937 was a "Vee" type running from the tip of each of the twin vertical stabilizers to a mast atop the fuselage, located at Station 176. The antenna was, therefore, a total of 46 feet, doubled back onto itself. This length did not include the lead-in wire which exited the aft fuselage through a feed-through insulator and connected to one leg of the Vee at a point a few feet from one of the vertical stabilizers [note that the feed point was changed after the Luke Field wreck]. This antenna was, then, already 15% longer than optimum; but since the radio equipment had been installed by Bell Labs, it can be fairly assumed that it was tuned properly at that time.

"The length of 46 feet was greater than 1/8 wavelength at 3105 KHz (approximately 38 feet) and greater than 1/4 wavelength at 6210 KHz (again, approximately 38 feet; this relationship is due to the fact that 6210 KHz is the exact second harmonic of 3105 and the wavelength at the higher frequency is half that of the lower); or, a non-resonant length at either frequency.

"This antenna was unsuitable for low-frequency 500 KHz operation, as the total length would be miniscule compared to the wavelength at this frequency. The wavelength of 3105 KHz is about 97 meters (315 feet), and about 48.5 meters (156 feet) at 6210. At 500 KHz, the wavelength is 600 meters (1950 feet)."[1]

Location of dorsal mast

There seems to be some disagreement about where the second world flight dorsal mast was located.

Sta. 129 Page 16 of TIGHAR Tracks Vol. 11, # 3.
Sta. 129.5 Mike Everette's research paper.
Sta. 125 Notation on Harney drawing of NR16020, port side
Gillespie, Forum, 7 Jan 2010.
"Lockheed assigned stations numbers based on the number of inches measured aft from the tip of the nose. Only places where there was a circumferential internal structure (formers and bulkheads) were given a station number. Sta. 129 5/8 was a fuselage former located 129 5/8 inches back from the tip of the nose. The position of the exact center of the mast depends on exactly where the mast was installed. The Harney drawing is based on the available photographs and shows the mast mounted a few inches forward of the double rivet line that marks the station. So, I was wrong and I was right and I was wrong. Technically there is no 'Sta. 125' but the center of the mast appears to have been--near as dammit--125 inches aft from the tip of the nose.
"The position of the antenna mast was derived from numerous photos of the aircraft. The information about stations on the Lockheed Model 10 is in "Catalog of Parts - Lockheed 'Electra' - Lockheed Aircraft Corporation".

Variant installations


Ric Gillespie, Forum, 21 January 2013
  • As delivered in July 1936, the airplane had two antennas - a trailing wire that deployed through the extreme end of the tail and a wire antenna that ran from the starboard-side pitot tube along the starboard side of the belly supported by two masts on the belly, one roughly amidships and the other centered under the cabin window. This latter - the starboard-side belly wire - is the only antenna that remained unchanged throughout the aircraft's service life.
  • In October 1936, a small loop antenna in a translucent faired dome was added on the top of the cabin for the Hooven Radio Compass. A belly wire antenna was added to the port side, parallel to the one on the starboard side.
  • Some time in January or February 1937, the dorsal vee antenna was added. Around this time, the deployment position for the trailing wire antenna was moved from the extreme tail to a mast protruding from the underside of the cabin.
  • In early March, the faired Hooven loop was removed and an open Bendix MN-5 loop was added to the top of the cockpit, slightly offset to the starboard side.
  • In the rebuild following the Luke Field crash, the port side belly antenna and the trailing wire antenna were not reinstalled.
  • At the time of the second world flight attempt the plane had three antennas - the starboard belly wire, the Bendix loop, and the dorsal vee.


"There is debate as to the exact nature of the receiving antennas aboard NR16020. One scenario deems it possible that the dorsal Vee antenna was not used for receiving at all, but transmitting only; and that the receiver was not connected through the antenna changeover relay, but directly to one or more antennas installed on the belly of the aircraft.

"This scenario also includes the hypothesis that the belly antennas were destroyed, unbeknownst to Earhart, when the masts or the wires made contact with the ground during the final takeoff from Lae, New Guinea. This scenario may explain why Earhart seems to have been unable to hear any transmissions from the U.S. Coast Guard Cutter Itasca at Howland Island, as she approached the end of this leg of her flight.

"The existence of the belly antennas is an established fact. However, they may not have been employed for communications reception at all, but rather as sense antennas for radio direction finding purposes. Unfortunately, no available source can confirm their exact function."[2]

TX = "used for transmission"
RX = "used for reception"
DF = "used for direction finding"
History of antenna configurations
July 24, 1936 Hooven RDF unit after Bell Labs after Gurr March 17, 1937 July 2, 1937
dorsal Vee TX (46') TX (+500 kcs) TX TX (54')
starboard ventral antenna TX/RX TX/RX RX RX RX RX
port ventral antenna DF DF DF DF removed
trailing wire TX 500, 3105, 6210 kcs TX 500 kcs TX 500 kcs TX 500 kcs TX 500 kcs removed
Hooven loop DF DF
exterior loop DF DF DF
  • Hooven Radio Compass installed in October, 1936. The Hooven direction finder employed a faired-in loop above the cockpit.
  • Bell Labs work: November, 1936.
  • At some point, the exit point for the trailing antenna was moved from the rear of the aircraft to a mast under the cabin.
  • Gurr: "We have seen other pictures showing the 'cigar shaped' DF unit installed on the underside of the airplane."[3] TIGHAR has not seen such pictures or confirmed the existence of an underside DF unit.

Discussion of the variants

Antenna feed point

Mike Everette says that "the lead-in wire which exited the aft fuselage through a feed-through insulator and connected to one leg of the Vee at a point a few feet from one of the vertical stabilizers."[4] But two photographs from the Purdue collection "show the feed connection at the V apex for the first world flight dorsal antenna configuration (bottom wire in each photo goes back to the feed-through in the cabin roof near Sta. 239)":[5]

"The antenna feed point was changed. Prior to the Luke Field wreck the dorsal vee fed into the fuselage at a point on the top of the fuselage just above and forward of the starboard side cabin window. The wire then ran down the interior cabin wall to the transmitter. When the airplane came out of the repair shop in Burbank in May the feed point had been altered so that the wire came down from the antenna and fed into the fuselage way down on the starboard side of the airplane just opposite where the transmitter was installed on the cabin floor."[6]

Directionality of the dorsal Vee

"Earhart's transmitting antenna was the dorsal "vee" and was, in fact, somewhat directional."[7]

Gurr's modifications

Joe Gurr made a number of changes in the radios and antennas at Earhart's request.

"The other part of the equation seems to be the changes that were made to Earhart’s transmitting antenna prior to her second World Flight attempt. Originally, Western Electric had set up the vee antenna that ran from a mast on top of the fuselage to each vertical fin on the tail to be an appropriate length for Earhart’s two primary communications frequencies, 3105 and 6210 Kcs. The much lower 500 Kcs frequency required a much longer antenna which was provided by a "trailing wire" that was played out into the slipstream after the aircraft was in flight and reeled back in before landing. The wreck in Hawaii that ended the first World Flight attempt also wiped out the mast on the belly from which the trailing wire was deployed. During repairs back in California the decision was made to eliminate the trailing wire and lengthen the vee antenna on top of the fuselage to accommodate all three frequencies on the one antenna. The mast that supported the point of the vee was moved forward several feet. It was a terrible compromise that provided no meaningful capability to transmit on 500 Kcs while greatly complicating the problem of putting out a decent signal on 3105 and 6210. There appears to have been, however, another consequence to lengthening the vee. The new length made an excellent antenna for the unintended harmonic frequencies."[8]

Chuck Varney, Forum, 6 January 2010.
If it can be shown that the WE 13C couldn't be loaded into the new antenna on 3105 kHz and 6210 kHz without modification or great difficulty then retain the first sentence; otherwise, delete it. If it can be shown somehow that the new length was a significantly better radiator of harmonics than the original, then retain the final two sentences--but first you need to know what the two lengths actually were, electrically. Otherwise, delete both of them as well.


  1. Mike Everette, A Technical Analysis of the Western Electric Radio Communications Equipment Installed on Board Lockheed Electra NR16020.
  2. Mike Everette, A Technical Analysis of the Western Electric Radio Communications Equipment Installed on Board Lockheed Electra NR16020.
  3. Gurr to Goerner, 29 March 1988
  4. Mike Everette, A Technical Analysis of the Western Electric Radio Communications Equipment Installed on Board Lockheed Electra NR16020.
  5. Chuck Varney, Forum.
  6. Ric Gillespie, 24 October 2000 Forum.
  7. Ric Gillespie, 26 April 2000 Forum.
  8. Ric Gillespie, "Propagation Analysis," November, 2000, TIGHAR Tracks.

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