Modifications by Joe Gurr

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Joseph H. Gurr was born circa 1901 and died circa 1988 (?). It seems likely that he married Marion E. Jacobsen in November of 1931;[1] Fred Goerner's last letter to Gurr says, "Hope all is well with you and Marion" (20 March 1988).

Gurr worked on Earhart's radios and antennas before both round-the-world attempts.

Career and qualifications

From the 3 May 1982 letter to Goerner.

  • 1914-1918: "Ever since I was a kid in High School, I had, and still have, an Amateur Radio Station on the air. I made it a point to keep up to date through technical papers and extra curriculum work in the field. Amateur Radio was one of the ways to keep my construction fingers busy."
  • 1918-1922: "Four years at sea as a radioman in the Navy. I was discharged in 1922 as Chief Radioman before I was 21 years old. I had already taken my examination and obtained my First Class Radiotelegraph License in New York, in preparation for a life at sea."
  • 1929-1936: "I became involved in engineering and construction of the prototype of two way, high frequency--as we called it in those days--radio telephone equipment with Boeing Air Transport in Oakland, California.
  • 1935: "There were commercial consultant jobs that seemed to pop up every so often. Some of them rather interesting, like being involved in the installation of a television transmitter in Bakersfield, California. I worked with Dr. Lee DeForest, who was the designer. The equipment was monstrous, but we made it work and we had a picture."
    • Gurr was involved with "a few pilots in the Bendix Air Races flown annually from Burbank to Cleveland. I did a bit of radio work, flight planning and radio range work for them."
  • 1936: Flight Dispatcher in Burbank, California. "This was a new activity in Flight Operations, and Boeing School of Aeronautics took on the job of instructing the men assigned to these new jobs. We completed courses in Aeronautical Meteorology, Advanced Meteorology, Radio Direction Finding, Dead Reckoning Avigation, Avigation and Celestial Avigation. We attended the same classes as pilots in equipment familiarization. With the exception of actual piloting the airplane, we were required to be qualified in every phase of flight operations and ground operations as well. It was an interesting and busy life, long hours of work and home work, and we all loved it. We were helping to build an airline, and we knew it."
  • 1937: "I had a full time job with United Air Lines, and had very little spare time."
    • John Kimmel, United Air Lines Station Manager in Burbank in charge of ground operations and a "good friend," introduced Gurr to Earhart and Putnam at Mantz's office.
    • Gurr fixed a dead receiver in the Electra by plugging in the antenna wire. The receiver was under the co-pilot's seat. Either no one had connected the antenna or it had become loose accidentally.
  • "I am listing below the licenses I have held for many years, and still have them. Except for my Private Pilot's License which would require an aeronautical physical to make current, all others are still valid."
Radiotelegraph First Class--FCC
Radiotelephone First Class--FCC
Amateur Advanced Class--FCC
Aircraft Dispatcher--FAA
Power Plant Mechanics--FAA
Airman Certificate, Private Pilot--FAA
Boeing School of Aeronautics Certificate of Competency:
Aeronautical Meteorology Meteorology
Advanced Celestial Navigation
Avigation (Avigation is "the science of aerial navigation.")
Dead Reckoning Avigation
Radio Direction Finding

Gurr's recollections about the modifications

3 May 1982 letter to Goerner

  • Gurr says he was reluctant to talk about his involvement with the radio equipment on NR16020. "Goerner found my name in Lockheed's engineering file in 1969." Goerner interviewed Gurr on 19 January 1970, sent him some questions that Gurr answered in longhand, and corresponded with him several times in the 1980s; the last letter from Goerner to Gurr is dated 20 March 1988.[2]

Modifications prior to first attempt

Installed loading coil for dorsal antenna / 500 kHz
Because of the mechanical unreliability of the trailing wire antenna, Gurr "improvised a loading coil and resonated the top antenna system. Obviously this was not a very efficient radiator, but I pointed out to Amelia that there was not much more than 50 watts of power and at that frequency the range would be limited, even with the more efficient long wire. Furthermore, the only people she could raise on 500KH would be ships at sea, and then she would have to be on top of them to be heard. This is what she wanted, because, as she put it, 'if we see a ship, we can verify our position.'"
Left trailing antenna intact
"I left the trailing wire reel installed, and it could be used. In fact, on one of our test flights, I unreeled this antenna and tried to raise someone on 500 kHz without success. 500 kHz is a frequency used for emergency communication. Ships at sea monitor this frequency with automatic equipment, but the radio operator still has to react. My sea experience showed 500 kHz to be a poor performer unless you can put out a strong signal to trip the auto alarm over any real distance, especially in daytime when low frequency propagation is poor, and it would be an advantage to be in busy shipping lanes. Amelia was sold and wanted the 500 kHz capability, and I gave it to her as efficiently as possible under the limited circumstances."
Saw Navy receiver installed?
"About this time we received a box marked U.S. Navy, containing a fine multi-frequency receiver, covering frequencies up to 20 megahertz. I do not know who was responsible for this acquisition, nor where it came from. I was pleased, as now the plane was capable of covering larger segments of frequencies which could be useful in radio communication, and even in radio direction finding. While the direction finding loop was designed for the lower frequencies, I found I could get a fairly good null on AM Broadcast Stations up to 1500KH. I figured it would probably be useful even on 3105KH if the received signal was strong enough."
"The original DF receiver was a 200-400 KC, plus 3105 and 6210 capability mounted under the copilots seat. It worked OK. Along about then, we received a box marked "NAVY" containing a beautiful multi-band receiver. I never knew the model number but was definitely impressed. ... The receiver was a six band job covering 1.5 to 15 MH. (150 to 15,000 KC) For me it was easy, but I'm afraid Amelia did not quite understand the how of it. Her final reply was 'we will have lots of time en route to learn all about it.' True--en route OAKLAND to LAE was certainly time enough to learn how to tune that very fine, and really simple receiver. ... I did not personally install the receiver. Lockheed did, with a certain amount of advisory help from me."[3]
Tested equipment in flight
"When things were ready, Paul Mantz asked me to be his co-pilot on a long test flight. This was to be the final test flight. Captain Harry Manning would occupy the navigator's position (behind the fuel tanks) where he could make observations and would also use the transmitter, either phone or CW (code). There was a telegraph key mounted on the table. Voice communication could also be had from the cockpit. I personally checked Harry Manning in the operation of the transmitter which was installed just above the navigator's table. He could switch the transmitter from top antenna, or trailing wire from this position if so desired. We would leave Burbank around 2 A.M. and head out to sea. Manning gave Paul compass headings for Honolulu. Mantz tested engines and flight characteristics of the plane. We carried reduced fuel (not full tanks) but each tank had an amount so we could run on one tank for so long, and switch to other tanks.
"My assignment was to operate the radio, take bearings, and make radio contacts with FCC range stations on 3105MH and later on 6210MH. We flew out for three hours. Next Harry Manning would give us compass heading for San Francisco. I had an opportunity to find out just how the radio equipment performed over greater distances. We were about 400 miles out and from this distance the radio performed poorly. As we got closer, things got better and I was able to contact FCC stations quite well, both ways. I was able to take bearings on broadcast stations using the belly sensing antenna, and switching over to the loop. We flew right over the middle of the Golden Gate Bridge and headed south to Burbank. I was satisfied that the radio worked as well as could be expected considering power available and not the best of antennas."
Was the loop mentioned by Gurr the external Bendix loop? Date of change from Hooven Radio Compass to Bendix external loop?

Modifications after Luke Field crash

"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."

Redesign of dorsal antenna: 50% longer

"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."

Everette's objections

Mike Everette criticizes Gurr's account of the changes he made in the dorsal antenna:[4]

  • The antenna was lengthened from 46' to 54'--not 50%, as Gurr claimed.
  • 54' is not a resonant length for any of the transmissions frequencies (500 kcs, 3105 kcs, 6210 kcs).
  • The change did not materially improve the effectiveness of the antenna in the 500 kcs range and probably degraded performance on the voice frequencies.

New loading coil

"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."

Belly sensing antenna

"We designed a belly sensing antenna for preliminary reception of signals to be used for direction finding."

Trailing wire antenna left intact

"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."

Removed Morse code key

"I took the key out, with Amelia's consent. It could be that somewhere along the route the code capability was made available. I did not alter any wiring in the transmitter, merely took the key out. That is the key which I still have" (Gurr to Goerner, 12 September 1985). Gurr also mentioned having the key in his handwritten responses to Goerner's typed questions (see below for excerpts).
Could Earhart or Noonan have transmitted code without the key?
"Mr. Monsees mentioned that the CW signal he heard was 'shakey' as if the sender was new at manipulating the telegraph key. The sending was very slow. The thought occurs to me that it would be possible to transmit CW without the use of a telegraph key, by coding with the pushbutton of the voice microphone. ... that installation was Amplitude Modulation (AM). Pressing the mike button puts a CW (carrier) signal on the air. ... Maybe Noonan knew the code. I don't know. ... Your letter says Mr. Monsees intercepted the distress signals on July 7th."

Training Earhart on the radio system prior to March 17, 1937

"Amelia must have had many opportunities before the flight, and while en route, to consult and receive instruction in the use of the radio equipment, from people very likely better qualified than I."
"I had been after Amelia to check her out in the operation and use of the radio equipment-how to turn things on, to tune the receiver, operation of the transmitter and especially how to use the direction finding equipment, check out in the procedures and what she can expect-what the limitations were. I finally got her into the airplane on the ramp at Paul Mantz's, and we went to work. We had hardly covered the preliminaries, perhaps one hour's worth, when Amelia had to leave. She was hard to pin down because she was obviously in demand at other places. We never covered actual operation such as taking a bearing with the direction finder, not even contacting another radio station. I was disappointed, but Amelia said she would have lots of time while aloft to figure things out. I was not too concerned. Harry Manning had the operation down quite well, and of course there would be ample time for familiarization with the equipment while enroute. Harry and I covered such things as ambiguity of bearings and flying triangular courses in order to obtain a proper signal source direction."

Critical remarks on Noonan

Shortly before Amelia's departure for Oakland to start her flight westward, a new face appeared on the scene. It was Fred Noonan. His reputation preceded him via the grapevine and was not very complimentary. If this was true, we wondered why Amelia would consider taking him along. Fred, you covered the story of Noonan's drinking, and this type of thing was intolerable where I worked-both pilots and flight dispatchers. It was the quickest and most sure way to lose your job regardless of seniority or anything else. We hoped that Amelia knew all this, but then Harry Manning was along, so we had no concern. Noonan was supposed to be an excellent navigator, however we already had an excellent navigator aboard, plus Harry Manning had a private pilot's license and could therefore help with the flying, relieving Amelia a spell here and there. He knew how to operate the radio, both voice and code, the latter having greater range. On top of his obvious qualifications, Harry was a very level headed and stable person. He was a real asset to Amelia's undertaking. As I mentioned, Harry and I became good friends, and he confided to me that he did not understand why Noonan was coming along. The weight alone of another person aboard could make a difference under certain circumstances. Anyway, my work was finished. I was never even introduced to Noonan. I did not see him in the final preparations at Burbank. I could now only hope for the best.

Gurr's speculations on the loss of the aircraft

Would the aircraft stay afloat?

"On July 4th 1937 George Palmer Putnam telephoned me in Burbank. I already knew that Amelia was way over due at Howland Island. Palmer wanted my opinion of what I thought might have happened, and if I could shed any light on what emergency measures Amelia and Noonan might be capable of taking, Did I have any idea where Amelia could have possibly landed at sea. I could not answer the latter. We could only discuss how long the airplane could stay afloat, assuming that a reasonable water landing was made. Empty gasoline tanks would be good flotation gear, however I could only venture that the engines were heavy which would cease a nose heavy condition in the water. Also, the tanks had vent openings through which water could fill them in a certain length of time. I do not know, but it is possible that the Lockheed engineers thought of, and installed a method of shutting off these vents as the tanks were used up, but I don't know this. There was not much light that I could shed on what was happening."

How long could the batteries last?

Telegram to Putnam, 5 July 1937
See the Purdue archives for a scan of the original telegram.

Burbank, California 5 July 1937 George P. Putman c/o Coast Guard's Oakland Airport, Oakland, California






Criticism of Earhart's skills

"Amelia had all the necessary equipment, apparently all in working order, but the skill factor simply was not there. Yes, I tried and tried to get Amelia into that airplane while it was in Burbank, to teach her the fundamentals of radio direction finding. I felt that the success of the project depended on a successful homing in on the Coast Guard Cutter Itasca at Howland Island.
"If you have ever flown over the ocean, as many of our United Air Lines Pilots did in the Air Transport Command operation during the war, you know that our pilots always homed in on radio range signals which were set up at all the tiny islands they were destined for. I mean ALWAYS. Literally thousands of flights were made, jumping from one tiny island to another. The fact that these flights were made over water had nothing to do with it. All that did matter was that each destination had a radio range to home in on. Of course they navigated, celestial and dead reckoning, but the last one or two hundred miles were flown on a radio beam. If for some reason the radio signal failed, or was unusable on one island, the flight planned and carried enough fuel to proceed to another island where the range was working. This was under visual flight conditions.
"Amelia absolutely had to home in on Howland. They navigated close enough, the strength of their radio signals showed that. At 7:58 A.M. July 2nd their signals were strong, and 50 watts of power at 3105 kilohertz at that time of the day had a limited range. Right here was the crucial period. If the Itasca heard them that well, they were definitely within range of radio signals from the Itasca, strong enough to easily take a heading via the direction finder. Finding Howland now depended on Radio Direction finding, and absolutely nothing else, smoke signals from the Itasca or anything else notwithstanding. Knowledge and accurate and precise use of DF was needed now, and there was a failure.
"Amelia knew that DF was vital to the operation at Howland. Therefore, we must assume that the equipment on board was functioning properly before leaving Lae, New Guinea. She must have realized that she could hardly expect to sight Howland by navigation alone, flying over 2550 miles distance, with no markers, unknown wind and cloud condition. DF bearings were her only salvation as she approached the vicinity of Howland Island.
"... I should have insisted on spending more time in instructing Amelia in the use of DF, knowing that, to a large degree, radio direction finding would sooner or later spell success or failure of the entire project. It was close.
"... Amelia and Noonan flew a great distance, with several stops en route, over countries with radio stations. Frequencies and tine of operation of stations all over the world are known and published. There was all kinds of time and every opportunity to practice the use of their direction finding equipment. By the time they reached Lae New Guinea, both Amelia and Noonan should have been expert in radio operation on that airplane.
" ... what happened at Howland? Amelia did all the radio work. Noonan was not a pilot, so we must assume Amelia did all the flying. Amelia was well checked out and versed in flying that airplane, but obviously she was not proficient in operation of the radio. From the logs I have seen, it was a poor performance. They could not seem to coordinate their radio conversations with Itasca, could not establish a meaningful two way conversation to enable them to perform a plan of operation with Itasca. I can only imagine what was happening in that cockpit during ring the last hour of flight, with fuel running low, two way communication failing, unable to get any outside opinion or help. They were lost. A fine airplane, operational radio gear, help standing by, every reason for success so close but for the human element that failed to produce at the critical moment."

Questions from Goerner, Answers from Gurr

Excerpts from Gurr's written interview with Fred Goerner (undated; after letter of 3 May 1982).

FG: In the days following the disappearance, Lockheed sources alleged that the Earhart plane could not broadcast on the surface of the water. This discounted the messages that were being received by amateur (ham) operators and Pan Am and Navy stations. When you spoke with GPP (George Palmer Putnam) on July 4, 1937, did you tell him that is was possible that Earhart and Noonan could broadcast if they were down at sea?

JG: I have my doubts that signals from that plane could reach out more than a couple hundred miles. Sometimes we have freak conditions of skip so I cannot discount the possibility that the signals were heard greater distances. I doubt some of those stories. A fellow by the name of Meyers called me with a rather fantastic story. I taped his conversation on a cassette.

FG: According to the Itasca (Coast Guard vessel) radio log, Earhart asked for homing signals to be sent to her on 7500. Did her DF have that range? Could she have taken a bearing on that frequency?

JG: Yes. That Navy receiver had 200-400KC up to 22 MC. The DF loop on the airplane was designed for low frequencies--200-400 KC. It would be much less efficient on 7500, and then the signal would have to be quite strong to overcome the greatly detuned (from resonance) condition.

FG: It has been alleged that AE left the CW key in Miami and that neither she or Noonan could send CW. Did the Earhart plane have a CW capability either through CW key or through depressing the voice phone, and what do you remember about the CW capabilities of Earhart and Noonan?

JG: Equipment had CW capability. Key, was taken off after Capt. Manning left, as [neither] Amelia nor Noonan knew enough code. I still have the key if you want it?

FG: The Itasca wanted Earhart to send on 500. Did the Earhart transmitter have that capability?

JG: Yes. Not much power. Transmitter output perhaps 50 watts. Antenna efficiency poor account too small. But I had it putting out OK. Yet it is quite possible that something could have been heard, as she was quite close to Howland

FG: It has been learned from Australian records that Earhart was having trouble with her DF when she flew into Port Darwin. It wasn't working at all. A Sgt. Stan Rose of the Australian Air Force checked it out and discovered that the DF had blown a fuse. He replaced the fuse and the DF worked well. Was this a common problem with the DF? Where was the fuse located? Was it somewhere AE or Noonan could replace it in flight?

JG: ... I never had a fuse blow. Usually the receiver would have its own fuse, and could easily be replaced.

Goerner's interview notes

Exceprts from Goerner's interview with Gurr at his home in Los Altos, 19 January 1970.

Thirteen gas tanks total: six in the wings (394 gallons) and seven in the fuselage (804 gallons) for a total capacity of 1198 gallons. After the Honolulu flight, one 51-gallon tank was removed from the fuselage, leaving the total capacity at 1147 gallons. Goerner noted that this accords with the Chater Report. Gurr also talked about the the 100-gallon tank that carried 50 gallons of 100 octane gas for takeoff.
"The Electra was absolutely capable of putting out a radio signal whether on the surface of the water, or on a reef or island. ... AE could not receive because the V antenna for that was beneath the aircraft. He also said it was possible that Earhart signals might be heard in the U.S. and not be heard in the immediate Pacific area because of skip characteristics."

Discussion of the modifications

The material seems to be authentic

Ric Gillespie, 22 July 1998 Forum.
The Gurr letter is a typed document signed by Gurr dated May 3, 1982. The Q and A document consists of typed questions from Goerner (different type-face than Gurr's letter) with handwritten responses under them from Gurr. It is undated and unsigned but the handwriting resembles Gurr's signature on the letter. Both documents appear to be authentic.

Belly antenna used for receiving

Vern Klein, 9 September 2000 Forum.
I guess we have to remember that what Joe Gurr had to say in his communications with Fred Goerner was all relative to the way the radio equipment was when he last knew of it in Burbank.
Of course, Gurr talks some about improvising to give Amelia some 500 kc transmitting capability without using a trailing-wire antenna. Nobody used voice on 500 kc. It was regarded as strictly CW.
"I was able to take bearings on broadcast stations using the belly antenna, and then switching over to the loop." Note that he says "switching over" not "switching in." I think he used the belly antenna only to get a station tuned in with that more efficient antenna, then "switched over" to the loop to take a bearing -- an ambiguous bearing except that he knew the station was up ahead, not behind.
To me, this suggests that the belly antenna was the receiving antenna and the "V" on top was the transmitting antenna. The T/R relay in the transmitter was not involved and the transmitter could have been heard by the receiver -- if it was not totally "blocked" by the strong signal.
Ric Gillespie
Good work Vern, and a strong argument for an antenna set up that matches the antenna loss at Lae with the problems encountered at Howland. ...
It looks, to me, increasingly like Earhart removed the Hooven Radio Compass, which entailed a separate receiver and a sense antenna, and replaced it with the new Bendix loop and coupler which used the existing WE20B receiver and did not employ a sense antenna. The belly antenna was the receiving antenna. When it was lost on takeoff at Lae, Earhart lost her ability to receive until the one brief moment when she "switched over" to the loop and heard the "A"s on 7500. She then switched back to the missing belly antenna and again heard nothing.

Consequences of lengthening the dorsal antenna

Ric Gillespie, 9 September 2000 Forum.
It was the opinion of an earlier TIGHAR-member researcher (who had extensive experience in avionics) that Gurr's lengthening of the dorsal Vee antenna would have really screwed up her ability to transmit effectively on 3105 and 6210 without giving her any real transmit capability on 500 kc.

In fairness to Gurr ...

"The alterations to the antenna system aboard NR16020, while well-intentioned, resulted in degraded performance of the transmitter. In fairness to Joseph Gurr, however, it must be remembered that Earhart was obsessed with saving weight and this was one main reason she left behind her trailing-wire antenna. Gurr was trying to help preserve her 500 KHz capability, to enable use of the only emergency frequency then available; but by lengthening the dorsal Vee antenna, he created other serious problems. His radio knowledge may have been more empirical than theoretical; therefore, he may not have realized the extent or cumulative effect of the problems created by his changes. This sort of empirical knowledge was typical of the times; but it was not adequate to deal with this situation."[5]

Related articles


  1. Collected from, a link that now seems to be dead.
  2. Ref needed to Smithsonian collection.
  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. Mike Everette, A Technical Analysis of the Western Electric Radio Communications Equipment Installed on Board Lockheed Electra NR16020.