[Doc Ewen looks into the horn antenna, 1950]
Image courtesy of Doc Ewen


Harvard Cyclotron: 1948-1951

Detection of HI Line: 1951

Harvard 24ft and 60ft and NRAO founding: 1952-1956

1950s and 1960s: Two Roads that Crossed

Microwave & Millimeter Wave Applications in the 1970s and 1980s

Mm Wave Radiometry in the 1990s

May 2001 visit to NRAO Green Bank



[Doc Ewen and horn antenna, 2001]
Image courtesy of Doc Ewen

Doc Ewen: The Horn, HI, and Other Events in US Radio Astronomy

by Doc Ewen, © 2003

Harvard Cyclotron: 1948 to 1951

My time at the Cyclotron Lab is the story of people that I met at the Lab and that became such a large part of my life then and in the future.

Warren Green, Director of the Amherst College Astronomy Dept., was very upset when he learned of my decision to pursue a future in law and to enter Harvard Law School in the fall of 1946. He sent me a long letter and enclosed an application for an NRC Fellowship. Out of respect for Warren, I sent in the application. A short time later I was quite surprised to receive a full tuition fellowship in physics. At the time I was on the staff of Vice Admiral Bowen, Director of ORI (later named ONR). My award sparked a lively discussion between Bowen and his aid Rear Admiral DeFlores, with Bowen favoring Harvard and DeFlores, MIT. I decided to study physics under Ken Bainbridge, a pen pal from my high school days. So, I went to Harvard. I first contacted Ken when I was a high school junior. I saw a picture of one of his gigantic mass spectrometers in a physics book. I sent him a letter asking that he answer some questions on the subject of absolute zero. He was very understanding. He encouraged me to look into some related subjects that would aid in our further discussions. I did and we continued to communicate, until I went off to college and realized how much I had to learn before I asked questions like that.

When I arrived at Harvard in ‘46 I signed up for Ken’s course on the introduction to atomic and nuclear physics. When I told him that I was the grown up high school student, with a BA in math and astronomy and three years with the Naval Air Corps, he smiled and said that it was his turn to ask questions. He was a great teacher and a fine person.

In 1947, Ken became the Director of the Cyclotron Lab, then under construction. In 1948, I was looking for a job that would fund an improvement in my lifestyle. I had discussed the problem with NRC and the best they could offer was $50 more per month, if I would get married. Ken offered me a continuation of bachelorhood and a 35 hour per week job at the Cyclotron Lab. I resigned my NRC fellowship and joined forces with Ken. He introduced me to Norm Ramsey who would take over as Director of the Lab in 1949. Norm in turn introduced me to Lee Davenport and Al Pote. Lee was the real Director of the Lab under Ramsey. Though he had some lesser title, Norm let him run the show. Al Pote was the bigger than life director of all electrical design. We would work on many things together in the years ahead. The same is true of Bob Grenzback, the brilliant mechanical engineer responsible for the mechanical design of this gigantic machine.

My contributions to the Cyclotron construction project were the method for frequency modulation (see letter to Pote in the ppt slides 7-10) and the development of the first external beam in 1951. The beam was very weak, but usable. More sophisticated techniques were to follow. My brute force approach is described in the ppt.

Most of 1949 was spent studying quantum mechanics under Julian Schwinger. During that year, I also discussed thesis topics with Ken Bainbridge. I was looking for something that would call on my knowledge of math, meteorology, astronomy, electronics and physics.

My background in math, meteorology and astronomy came from my year on the faculty at Amherst, which began in my senior year. One of the Astronomy Dept. professors, John Hall, was asked to join the staff of the MIT Radiation Lab during the summer of ‘42. At that time, I was taking a summer session offered to those who wanted to graduate early and get on with the War. Stan King, president of Amherst, called me to his office in the late summer of ’42 and offered me a position on the faculty in the Dept. of Astronomy. He did not seem concerned with details, like a student being a member of the faculty, or what it would be like to have peers and fraternity brothers in my classes. He recommended that I consider smoking a pipe. He showed me how one can take time to fill and light a pipe, as a means to obtain time to consider the most appropriate answer to an unanticipated question. During my year on the Amherst faculty I was an avid pipe smoker.

The Navy provided my background in electronics, with courses at Princeton and MIT and hands on experience in England with a patrol bombing squadron of 18 Liberators.

My knowledge of physics began at Harvard in ‘46. The popularity of quantum mechanics at the time left noticeable gaps in my knowledge of classical physics. I became known as the "quantum baby". I was more familiar with relativistic theory and quantum mechanics than with their classic counterparts in dynamics, electromagnetics and thermodynamics. The common language of mathematics was a life saver.

Ken Bainbridge had the answer to my challenge for a doctorate topic. He introduced me to Edward M. Purcell, a former doctorate candidate under Bainbridge. Ed was a marvel, both as a physicist and as a very sensitive person. I had taken courses given by Ed and also knew him quite well at the Cyclotron Lab where he was on the Scientific Advisory Committee. The conceptual design of the external beam machine that I built in 1950 was based on many discussions with Purcell. He taught me the value of the quick twiddle, the simple approach and the dry stone. The "dry stone" approach was an important part of our joint efforts on the Hydrogen Line project. I had tried two initial configurations in an attempt to detect the line. The second may have worked, but I was not certain. The data record in June of 1950 looked suspiciously like a line, but not solid enough for me to mention it to Purcell. Additionally, Norm Ramsey was beginning to lean on me for the external beam. In the fall of ‘50, I discussed our progress with Ed and recommended we consider a negative thesis. He asked the right questions that led to the right answer. First, he wanted to know if I was convinced that the line was undetectable. My immediate answer was no. He then wanted to know if there was anything that I could do to modify the machine so that its failure to detect the line would convince me that the line was undetectable. My immediate answer was yes, but that it would be very expensive. It would cost $300, and the modification would take two months. In my design, I had configured the middle part of the signal processing chain, from the IF input to the Video output around a commercially available communications receiver built by the National Radio Company in Waltham. The receiver model that I was using was called an HRO. That receiver was owned by the Cyclotron Lab I would borrow the HRO and other test equipments from the Cyclotron Lab, on the weekend and move them to my fourth floor Lab in Lyman, just a few hundred feet south on Oxford Street. I wanted to make some changes in the circuit of the communications receiver, in particular the method of switching the first local oscillator in the double conversion super heterodyne. I was convinced that the failure to detect the line was the broadband nature of the line, requiring that the comparison channel when scanning the line should be at least 75 KHz from the signal channel. If the two channel frequencies are too close together, the comparison is between one part of the line with another part of the same line. My channel separation frequency at the time was only 10 KHz.

The modification I planned to introduce would be viewed as a major change. I was unable to come up with a plug-in approach that I could introduce on the weekend and return the receiver to normal operation at the Cyclotron Lab during the week. The simple answer would be to buy our own receiver, hence, the $300.

Ed asked that I drop by in the morning and he would have an answer to my request. That session began with a discussion of the dry stone and the importance of putting a solid quotable number on any publication. I assured Ed that we would not have to crawl out from under a wet stone if he could locate $300. He took out his wallet and gave me $300 in cash, with the comment, "Keep the stone dry." I was obviously startled, but managed a, "Yes Sir," as I took off for the National Radio Company. With help from the Cyclotron Lab in moving test equipment back and forth between the Cyclotron Lab and Lyman, the modification was completed during the Thanksgiving holidays. Integrating the modified receiver into the 21 cm radio telescope would take several days. It would have to wait for the Christmas holidays, when I could get long term (several days) use of test equipment from the Cyclotron Lab I returned to the Cyclotron Lab to work on the external beam machine.

During a status meeting with Norm Ramsey, I informed him of a recent request from the Navy that I return to active duty. It was agreed that I would work only on the external beam, until that project was successfully completed. It was also agreed that handwritten documentation would be too time consuming. Details of the design would be documented with the aid of a 3D camera, that would be purchased by the Lab for that purpose. As a result, all of the important equipment photos of the external beam machine and the 21 cm line project were taken in 3D. Many of these were transferred to 2D on a CD by a company in Northampton, MA for both the NRAO and Cyclotron presentations.

The slides associated with this text are confined to hardware. For anyone who was there, the attraction was the people. We had a team that could do anything. We had the best of scientific advisors and the best in technical management. It was the place to be to learn and to share knowledge.

The slides were prepared as a support document for presentations to the Association of American Physics Teachers, and for the Gordon Lecture at the Arecibo Radio Observatory in 2002. Selected slides were used during the QA period.

View related slides

Modified on Wednesday, 11-Aug-2004 16:49:43 EDT by Ellen Bouton