Interview with John D. Kraus
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The interview listed below was either transcribed as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) or was transcribed in the NRAO Archives by Sierra Smith in 2012-2013. The transcription may have been read and edited for clarity by Sullivan, and may have also been read and edited by the interviewee. Any notes added in the reading/editing process by Sullivan, the interviewee, or others who read the transcript have been included in brackets. If the interview was transcribed for Sullivan, the original typescript of the interview is available in the NRAO Archives. Sullivan's notes about each interview are available on the individual interviewee's Web page. During processing, full names of institutions and people were added in brackets and if especially long the interview was split into parts reflecting the sides of the original audio cassette tapes. We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of the original cassette tapes, and for a 2012 grant from American Institute of Physics, Center for the History of Physics, which funded the work of posting these interviews to the Web.
Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event.
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First question/answer not audible on tape:
Sullivan
I think the first place to start is if you would please repeat for me the experiment you did in the early ‘30s concerning solar radiation of which I think there is no published records. Is there?
Kraus
I have made reference to it in a couple of my books but it's sort of like a footnote, something of that type.
Audio of interview begins here:
Sullivan
What exactly was this experiment?
Kraus
Well, I'm trying to pinpoint the year. I'd have to think about that a bit. It was around 1934 I presume and I was a post-doctoral research associate in the Physics Department at the University of Michigan, working on the cyclotron. And one of the other students there, Arthur Adel, approached me to inquire if I'd give him some help setting up some equipment to look for radio waves from the Sun. He had a belief that in the region of sunspots due to the motions involved, the particle velocities and likely presence of strong magnetic fields there, that there might be radio emission. And coincident with that there was a 1 meter [Sullivan: 1 centimeter] radio apparatus available in the department which Cleeton and Williams had built which they had used for the detection of the 1.3 cm ammonia line. They had a gas cell which they suspended between two 1 meter diameter World War I searchlight parabolic reflectors. They transmitted the waves in this beam between the two reflectors and we proposed to use one reflector with the receiving equipment, a crystal detector and galvanometer and see if we could detect any radio emission from the Sun. Well, we made the attempt and our results were negative. But the idea behind it was sound. The problem was that our equipment, which was about the best of the state of the art afforded at the time was about 60 dB too insensitive.
Sullivan
What exactly was the receiver?
Kraus
It was just simply a crystal rectifier connected directly to a very sensitive, microampere-type, galvanometer which was adequate to pick up the radio emission from the magnetron tubes that Cleeton had built to transmit through the gas bank holding the ammonia.
Sullivan
The ammonia work was published, I suppose? So I can find the description of the thing there?
Kraus
Yes, that is right. There is this article by Cleeton and Williams on that. I am not exactly sure about my date; it may have been a year later than this but it was right in there. I'd have to check that. The mid ‘30s.
Sullivan
Was he looking for activity associated with a flare or only with sunspots?
Kraus
Well, our beam was wide enough that all we could pick up was the Sun; we couldn't distinguish - just radio emission from the sun at centimeter wavelength, that's all.
Sullivan
Right. You weren't waiting for a flare?
Kraus
No. It's curious because at the time I was also doing some work at 5 meter wavelengths with my amateur radio equipment. I was developing some types of antennas, beam antennas as a matter of fact. And with the state of the art in receivers at 5 meter wavelength and one of my beam antennas, I had a better chance of picking up emission from the Sun at that time except that it happened to be at a sunspot minimum. However, if I'd done that experiment a few years later at a sunspot maximum then the chances might have been pretty good. So you see, you needed not only the idea but you needed to do it at the proper wavelength and at the proper time in the spot cycle to make it pay off. And Jansky as a matter of fact with his equipment would probably have detected the Sun if he had been operating during the spot maximum.
Sullivan
That's right. And this was post-Jansky, your solar attempt?
Kraus
Yes.
Sullivan
So you were influenced by the fact that radio waves were...
Kraus
This is quite likely since extraterrestrial waves had been detected. Well, Jansky's idea at the time was that they were from- this could very likely be from radiation from stars except that he didn't detect any from the Sun, and therefore unless the Sun were not a typical star, it meant that it probably came from the interstellar medium. And in that respect he was correct.
Sullivan
Did you know of any other attempts earlier or simultaneous to detect the Sun at this time?
Kraus
No.
Sullivan
Do you know of any attempts of pre-World War II?
Kraus
No.
Sullivan
So that was one incursion. But when was the next time you got involved in radio astronomy?
Kraus
During the War I was working at the Naval Ordnance Laboratory [NOL] in Washington. We were doing de-gaussing, that is the protection of ships against magnetic mines. And this was a laboratory which had been assembled; the personnel had been assembled very quickly, actually somewhat before the United States got involved in the War in order to develop methods to protect ships against magnetic mines.
Sullivan
The Lend-Lease thing? Were you going to England and so forth?
Kraus
Oh, yes, to protect any of the ships because the water surrounding were being mined with these and they were very difficult to combat. Well, one of the other men recruited for the Naval Ordnance Laboratory was Grote Reber.
Sullivan
I see.
Kraus
We worked in the Laboratory long hours. But when we were out of the Laboratory, because we were working on the top secret project, we refrained from saying anything about that. For a topic of conversation, Reber turned to his experiments in radio astronomy and what he was doing, had done. It was a fascinating story, and if there hadn't been a war and I had been involved, I would have liked to have done something about it right then- build a radio telescope or work on some of this. So it was not until after the war...
Sullivan
Let me just ask now, Reber did observations in '42, '43, and '44 so he must have gone back very soon.
Kraus
Yes. He was at the Naval Ordnance Laboratory for a period and then he returned to the Chicago area. He lived in Wheaton, Illinois. He worked at one of the large radio companies in the Chicago area.
Sullivan
But you stayed on at the Lab throughout the War?
Kraus
Well, I was at Naval Ordnance Laboratory from '41, '42. I was there for three years and then the last three years of the War, I was at the Radio Research Laboratory at Harvard University.
Sullivan
What was this purpose?
Kraus
At NOL we were working on protection against magnetic mines. This was a counter-measure activity. And at Harvard we were doing radar counter-measure protection against radar by means of nullifying the value of radar equipment.
Sullivan
I suppose this is in close conjunction with the Rad Lab at MIT?
Kraus
Well, they were operated entirely separately and we knew about their radars because we could pick them up in working out ways of jamming them and other things but they didn't know too much about our work. It was that kind of an arrangement. Well anyhow, I came to Ohio State after the War and I was deeply engaged in starting some courses in electromagnetic theory and teaching; and it wasn't for several years after I came that I was able to do any serious work about radio astronomy. But in the early ‘50s...
Sullivan
But you were following it I suppose?
Kraus
Well, I had heard about the things that were being done mostly in England and Australia. So about 1951, I presume would be pretty close to it, I started work with a graduate student or two in building an array of helical antennas to detect the Sun and what other objects we might be able to receive with the equipment that we had.
Sullivan
What specifically was going to be the improvement in this antenna versus previous solar observations? What would it enable you to do?
Kraus
I don't think that we had any particular definite objective in mind. We just wanted to start observation, determine what needed from a more empirical basis. At the time we started, there were only two other universities in the United States that had done any work in radio astronomy. There had been some work at Harvard and Cornell.
Sullivan
You just wanted to get in the game yourself?
Kraus
We wanted to start and see what we needed. A few years earlier I had discovered or the word "invented" is probably more appropriate, a new antenna- the helical antenna, which is a circularly polarized, a broadband antenna with very low mutual impedance so that it can be used in large arrays very easily. It has many highly desirable features. And not knowing how many we would need, we started with an array of a dozen or so of these helices on a tiltable ground plane so that we could operate it as a meridian transit instrument. And our funding was modest and one on the first steps- well, the initial one that got us started was that we received a grant from a university fund for about $2,000. I converted that almost 100% into steel- a couple of tons of steel angle iron and beams; and with students working part-time, afternoons and weekends, we put this telescope together. We wound all the helices, and put them on. We got some receiving equipment and found we could first detect the Sun, then Cassiopeia A, Cygnus A, other radio sources. We realized that if we added more helices we could get more sources and we just continued on this for a period of a year or so, gradually adding more until we had almost a hundred- actually an array of 96 helical antennas on a big flat steel tiltable structure, 160 feet long and about 22 feet wide. It was one of the world's big radio telescopes at the time. And with that we were able to detect the order of 100 or so radio sources.
Sullivan
Over what period was the antenna built now?
Kraus
The antenna was built in the period starting from 1951 to 1953.
Sullivan
And you published these results I assume?
Kraus
Well, we did some. One of the most complete things we did was a survey of the sky at the wavelength we were operating, about 250 MHz- that's about 1.3 meters. We made a survey of the whole sky that we could reach with this and published this map showing the position of the radio sources, the discrete sources, that could be picked up. It was a beautiful map in the sense that you could see the Galaxy so clear and so strongly. In the year that this came out, which was about 1955 perhaps, Harlow Shapley picked it as one of the year's 10 most outstanding accomplishments in astronomy which gave us a real boost and impetus. There was a lot of interest by many people in this new area of radio astronomy.
Sullivan
This was the map that has been made into an intensity display also?
Kraus
Yeah, we took that and converted the contour map into shades of light and black and so we then subsequently published it as an impression of how the sky would look if your eyes were sensitive to radio waves instead of light. It's really a beautiful picture. It gives you in a glance the great difference between the radio sky and the optical one.
Sullivan
What about your radio source, you said you'd detected 100 sources, did you publish a source list?
Kraus
We published a number of these. There were none of them that were really discoveries on our part. It was a matter of confirming the observations that had been made by other observatories. But we were operating at a different wavelength, and so by our measuring the flux density there we were able to put another point on the radio spectra. We got interested early in the game on spectra of radio sources. This radio telescope was located on some property owned by the Agriculture College of the University. It was not too far from the main campus of Ohio State University and in an area that was rapidly developing and urbanizing. And I realized if we wanted to continue our work with a bigger telescope, it would be better to locate further away. So I was encouraged to consider a site near the Perkins Optical Observatory which is near the town of Delaware, Ohio about 20 miles north of Columbus, by Dr. Geoffrey Keller, who was at that time Director of the Perkins Observatory. The Astronomy Department at OSU was still a part of physics; it was the Department of Physics and Astronomy. The Perkins Observatory is owned by Ohio Wesleyan University. Ohio Wesleyan is an undergraduate school and Perkins Observatory had this big optical telescope. When it was built some years earlier, it was the third largest telescope in the world, I think, 69 inch and strictly a research instrument. So some years earlier, this would be probably in the early ‘50s, Ohio Wesleyan made arrangements with Ohio State to staff and operate the telescope. I talked with the administration of Ohio Wesleyan about some land for a radio telescope and they were very cooperative and so they made available to us about a 20 acre tract near the Perkins Observatory where we could build our radio telescope. The most attractive feature of the whole thing was that this was in the middle of a big tract of land owned and controlled by Ohio Wesleyan, which I felt might serve as a buffer against encroachment by sources of interference. So about 1956 we started construction of a bigger telescope and I had been contemplating a design of a larger instrument and evolved one which has a large fixed standing parabola and a tiltable flat reflector joined by a ground plane. The whole motivation of it is to get the largest aperture possible per dollar of cost. And so if you keep the instrument close to the ground you reduce the height. Cost usually goes up as height cubed, at least.
Sullivan
And this was a unique design, was it not that you came up with?
Kraus
It was a unique design, yes. It has been adopted by others, in France a couple of telescopes have been built of this design. One of them considerably bigger than ours.
Sullivan
Let me just ask, did you have any contact with optical astronomers at all during the first few years?
Kraus
Well, I mentioned Dr. Geoffrey Keller. Yes, I did and the Astronomy Department was interested. I was made Professor of Physics, Astronomy, and Electrical Engineering so I had appointments in all three departments.
Sullivan
So there was an innovation even at that early stage?
Kraus
Yes. The funding for our work came out of electrical engineering but at the intellectual level and at the level of the astronomy and the work being done, it was closely integrated with the optical astronomy. Unfortunately, the climate in Ohio had an adverse effect in the interests of the optical astronomers for the most part. I mean they were interested in the radio astronomy but none of them had research or were doing work in areas that turned out to be directly related to radio astronomy. And this is really a kind of curious thing. Because of the poor climate, poor seeing in Ohio, the optical work had concentrated on spectra of bright stars. Well, these have turned out to be not very good radio emitters. If we'd had better seeing there it might have been that some of them would have been interested in nebulosity. And those were the things that you see in the early days we began to identify with radio sources. So there wasn't the opportunity for direct collaboration. But nevertheless there was interest and we participated in their colloquia and discussions and I sought advice on the interpretation of our results.
Sullivan
That's interesting because many other places there really wasn't much contact at all in the early 50s between the optical and radio people. But now back to your dish...
Kraus
Well we...
Sullivan
The money for that came from where, ONR [Office of Naval Research]?
Kraus
No. About 1957, I think somewhere in there, we began to get a small amount, maybe '56, from the National Science Foundation [NSF] which allowed us to make some preliminary moves. And for a number of years we got funding from the NSF which allowed us to proceed with the construction of this large telescope- the standing parabola 360 feet long, 70 feet high, and a tiltable flat reflector. About the same length but 100 feet in slant height and connected by an aluminum covered ground plane 3.5 acres in extent. Well, this construction went on rather slowly over a period of many years because this is unique in the following respect; in many institutions instruments have been built by having someone write a set of specifications and then getting people, manufacturers to bid, getting the money, and having it constructed. Here we developed first of all the design ourselves and we did all the construction in-house, using students working part-time for most of the work. These were not just engineering students, they came from many different departments in the University. It turned out that our best welder had been a high steel worker in earlier years, a very expert welder. He was a pre-dental student. And he taught other students welding. We had a Saturday morning class until we got about a dozen students up to a certain level of competence in welding and we had students who were in industrial engineering who specialized in time and motion studies and they systematized the operation to make it as efficient as possible. And we just worked away at this for quite a few years. It was slow steady tedious work getting this telescope built and put together.
Sullivan
When was it finally finished?
Kraus
We started in '56. By '63 we had most of it constructed and by that time we were beginning to turn our attention to getting receivers.
Sullivan
That's a long time indeed.
Kraus
And one of the OSU graduates in electrical engineering had gone with Western Electric and became pre-eminent in the development design of parametric amplifiers. Did I say Western Electric?
Sullivan
Yes.
Kraus
I meant Bell Telephone Laboratories.
Sullivan
Who was this?
Kraus
Mickey [Michiyuki] Uenohara. ‘Mickey’ is his nicknamed is last name is Uenohara, U-E-N-O-H-A-R-A. And this is a type of parametric amplifier- very low noise. The Bell Labs was willing to put one of these amplifiers together for us if we bought the basic components that went in. Uenohara's group built it and I think we took delivery on that about 1963, which gave us as low a noise receiver as in operation anywhere at the time.
Sullivan
How low noise was it?
Kraus
It was - the receiver itself was probably 40-50° temperature, very low noise.
Sullivan
At what frequency?
Kraus
1400 MHz.
Sullivan
And the dish was designed to operate to how short a wavelength?
Kraus
We did not know exactly how short it would go but it was designed to go at least as short as 21 cm. It has turned out it can be used very usefully to about 10 cm wavelength.
Sullivan
Before you go any further I had a couple of other questions. Were there any particular troubles besides essentially just the slow pace that things went at in the design of the telescope that you didn't foresee?
Kraus
Oh, we had lots of troubles. It's a long tedious process, many mechanical problems in achieving, getting satisfactory design, years of really slogging through the mud at the site; it's a big site with all the construction going on. And the fact that it was going on at a slow pace. But nevertheless we progressed.
Sullivan
None of the problems were so serious that they couldn't be surmounted anyway?
Kraus
Well, it just took patience and perseverance, and a lot of that- that is it took us longer than we had anticipated but we had no set time-table when we started. We got it done when we got it done. We made many preliminary observations with the telescope over a number of years and it wasn't until about 1966 when we put on a new reflecting surface, a good screened surface on the telescope, that we got the efficiency up to the point where it warranted it starting on a big sky survey. And that's what we started on at about that time and that continued for many years. We have just completed that within the last year.
Sullivan
I'm ending the history around '65 or so because it just gets out of hand after that. I still have a few other questions. What was the efficiency initially at 21 cm?
Kraus
The efficiency there was lower than we had hoped. It was less than 50% and after we got the new screen on we got it up around 60%, which is about as much as you could expect considering the fact you have to use tapered illumination to reduce side lobes. If you want to aim for 100% efficiency your side lobes would get you in big trouble.
Sullivan
Were you able to do any preliminary observations during these seven years that it was being built?
Kraus
Oh yes, we had a lot of publications on particular findings. We published preliminary lists... always with maps- that is, our surveys had been unique in that they are accompanied by contour maps of the sky...
Sullivan
Just a list?
Kraus
Not just a list of objects. And typically on these maps we plot the positions of all radio sources previously catalogued by other observatories. So in a glance when you look at this map you see not only our observationally results but everything that is known about the radio sky and that's what makes these quite useful.
Sullivan
What about the helix array? Did it just sort of die when you began on this other thing?
Kraus
Well, after we began to get in operation at the new site up near Delaware, we just de-commissioned it. But it was a very useful instrument for the period that we had it going. There are a few sidelights about this research and this sky survey. We didn't know exactly how many sources we would detect but it turns out that we had found about 20,000 radio sources at flux densities above about 2/10th of a Jansky at 1400 MHz in the sky which we have had surveyed between -35° to + 65° in declination. And at the present time this is the largest deepest radio survey that has ever been made. And out of this has come many very interesting sources that we noticed even the very first installments from this survey that we were picking up, quite strong sources, at 1400 MHz that were not catalogued at all in lower frequency surveys. And the reason for this was that these objects had flat spectra and were just too weak to be picked up at the lower frequencies. So that we early on started investigating these objects at higher frequencies than we could operate in a cooperative program with radio astronomers in Canada at the Algonquin Radio Observatory, primarily with Dr. Brian Andrew there. And some of these objects have turned out to be extremely unusual like OJ287 is one of the prototype erratic optical variables, it's a BL Lac type object.
Sullivan
And the high redshift quasars...
Kraus
And then we have found some very high redshift quasars, the two that hold the redshift record at the present time, OH471, with a redshift at 3.40, and OQ172, with a redshift of 3.53, are objects we found that were in no other surveys at all and might even now not have been really investigated. But when we found them in our survey, realized they weren't in lower frequency ones, we immediately concentrated on them and drew attention to them as being unusual. We got good enough positions at Algonquin to identify them with optical objects and this got some optical astronomers interested in obtaining optical spectra and finding that they did have big redshifts.
Sullivan
Going back to '56 was your motivation on all sky high frequency for that kind of survey?
Kraus
Well, yes. At that time we felt with this big instrument since it was a survey type of instrument, a meridian transit instrument, which couldn't be turned at will to look east or west of the meridian at this or that, that the best use for this type of instrument is a survey where you know you're going to look at the whole sky sooner or later so what you're looking at at the moment doesn't matter. And you just go at it systematically. And this was our main primary objective.
Sullivan
And so you just now, almost 20 years later, finally completed that, I guess.
Kraus
Well, I guess that's right. I hadn't realized it’s so darn long.
Sullivan
Were you influenced at all by the log N - log S controversy which was going just as you started this dish? Did you think that this might help?
Kraus
Yes, we thought it would. This is an elusive will-of-the-wisp that- we're getting closer to it but we have done work on this and it's very interesting.
Sullivan
But that was part of the original motivation also?
Kraus
Yes. Now you must realize in connection with this there have been many students working with me, graduate students and undergraduate students, and the names of these people will be in these publication lists. And one of them - a couple of them I'd like to mention- is H.C. Ko.
Sullivan
Is he still at Ohio State?
Kraus
Yes, he’s still at Ohio State. He worked on the earliest surveys with the helix telescope. And Robert Nash worked on some of the earlier surveys with the big telescope, the parabola type. And he did the bulk of the actual mechanical design on many of the structures. We worked together on that. He's an electrical engineer but also a very good mechanical engineer by the time he got through. And then Dr. Robert Dickson who is now Associate Director of our radio observatory and who is a very expert in the field of computers and programming, got our big sky survey worked out so that the data reduction could be done effectively with computer programs to reduce the data average records, discriminate against interference, and come up with a source list and actually computer plotted maps of the sky that we had surveyed so that these and many other people working together carried out the actual work.
Sullivan
Would you mind if I asked you about the Venus burst which you thought you had at one point? What were they actually? What's the story?
Kraus
They were terrestrial interference. And I was, how should I say- well, I had an instrument working which this was soon after the Jupiter burst had been picked up by [Bernard F.] Burke and [Kenneth] Franklin and we detected Jupiter on this and the natural follow-up, "Well, let's look at the other planets." Well, I never got anything from Mars because I could look at Mars at night when the Sun was down but Venus is a tough one because it's usually only up observable when the Sun is also up. And due to solar interference and also more of the daytime radio interference, it was simply a matter of seeing some bursts there that looked like they would correlate, that were interference of a solar type and/or a terrestrial interference and really not Venusian in origin.
Sullivan
I've heard someone say that you've actually pinned it down as to where this is coming from.
Kraus
No.
Sullivan
You never did?
Kraus
No.
Sullivan
Then what finally convinced you that it wasn't real?
Kraus
I just couldn't repeat the experiment.
Sullivan
I see. And so were the bursts a side lobe effect, a side lobe going on and off the Sun do you think or were they actual solar bursts?
Kraus
They were probably related to a solar burst in side lobes of the antenna. In other words a small amount of solar interference could just have been over-riding.
Sullivan
Another thing that I'd like to get the straight story on so to speak is I think there was a publication about the same time about a variable radio source. This flux was supposed to vary with time from the Ohio State Observatory, is this correct?
Kraus
We published a report about what appeared to be some variable flux density on a particular source that we had seen for - well I'd have to get the publication and look it over carefully. I don't know whether we thought more than one day. If it had been only for a single day I mean we would have discounted it as interference but it seemed to be there for a day or two and then was gone. We were scanning with the helix array and we didn't know. That is we weren't drawing any conclusions but we thought well, if this is real this is very interesting and I think we ought to publish it because it may alert others to look for similar things. So we didn't publish it with the idea that we had indeed a variable source. Here were some observations. Maybe it was a variable source. And it could have been. It could have been a flare type or something. Nobody knows.
Sullivan
And this was at a time when there were no variable sources except the Sun and Jupiter.
Kraus
That's right.
Sullivan
And, in fact, it wasn't until '65 when there were others found.
Kraus
But probability is that it could have been an interference effect too. In those early days there were so many things that we hadn't yet sorted out and when looking the records over we were trying to find everything we could and some of these had other explanations.
Sullivan
Well, I think that covers it quite well. Do you have any other comments you'd like to make?
Kraus
No.
Sullivan
Thank you very much. That ends the interview with John Kraus on 25 March, 1975 at the AAS Meeting in Bloomington [Indiana] and this is the end of the tape.