[Galt, 1957]
John Galt, 1957 (Photo courtesy of Tim Robishaw)



NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Interview with John A. Galt
At Onsala, Sweden
6 June 1973
Interview time: 21 Minutes
Transcribed by Alan H. Bridle

Note: The interview listed below was conducted as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) and was transcribed for the NRAO Archives by Alan H. Bridle in 2015. The transcript was reviewed and edited/corrected by Ellen N. Bouton. Any notes of correction or clarification added in the 2015 reviewing/editing process have been included in brackets; places where we are uncertain about what was said are indicated with parentheses and a question mark, e.g. (?) or (possible text?). Sullivan's notes about each interview are available on Sullivan's interviewee Web page. During processing, full names of institutions and people were added in brackets when they first appear. We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of Sullivan's original cassette tapes.

Please bear in mind that: 1) Transcript is of the spoken word rather than a literary product; 2) An interview must be approached 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.

Click below to listen to the full 21-minute audio of the 6 June 1973 interview.



Sullivan

This is beginning the interview with John Galt on 6th June 1973 at Onsala. You said that you didn't get involved in radio astronomy until 1958 or something like that.

Galt

Yes.

Sullivan

Exactly how was that?

Galt

Well, I went to Jodrell Bank to do post-graduate work and got involved with the hydrogen line group there. The telescope was not actually operative when we first got there but it was by the time I left. We worked with -

Sullivan

Are you talking about the Mark I?

Galt

Yes. The steel workers were still working on it and though there were receivers on it in the early stages it was still pointing at the zenith. The astronomers didn't have it until several months after I got there.

Sullivan

And your previous training had not been in astronomy or radio?

Galt

No it was in physics with a smattering of electronics, but not this.

Sullivan

How did you choose Jodrell Bank, then?

Galt

Well, let's see. I wanted to get into radio rstronomy. I had been interested in astronomy, and I had a background interest in radio too. So I wrote to Cambridge, Leiden and Jodrell Bank, and Jodrell Bank was the first one to reply positively (laughs).

Sullivan

Now what did you do at Jodrell? You say the dish wasn't working.

Galt

I spent most of the time making receivers for hydrogen lines with the idea of measuring the Zeeman effect at the 21-cm line. And of course a real definite Zeeman effect was not discovered until a good many years later. We were the first to try it. The amount of money that went into the steel work compared to the amount of money that went into the receivers was much greater. And it was a little bit of a shock to see the way they operated. We were working in little huts, smaller than this building here, but they were electrically heated and whenever there was a power shortage the power plant would phone us up and tell us to turn off our soldering irons (laughter). How we were supposed to do electronics without soldering irons wasn't obvious.

Sullivan

Now you say the Zeeman effect. What did you have? Very narrow band filters?

Galt

Yes. We'd hoped to have well, we switched. We had one narrow band filter and we switched between the two sides of the narrow absorption line in Cassiopeia. And there was - nothing showed up above the lines, and actually when Verschuur finally discovered it, it was 10 or 20 times lower than our noise level.

Sullivan

And did you publish that?

Galt

Yes.

Sullivan

Anything else at Jodrell?

Galt

Well, Jennison was probably the most clever person there. He was working with hydrogen line receivers then but he had before that been working on the early post-detection correlation interferometers, and his antennas were still around at the time. I don't think they were ever used since, but he tells one story of losing a whole out-station to thieves. They took the antenna and the power generator, the receivers and everything.

Sullivan

Must be hams or something.

Galt

Well, perhaps.

Sullivan

Then after a year at Jodrell -

Galt

Yes, I went back to Penticton well not back, I had never been there. Penticton was just starting and I had gone to Jodrell because there was nothing much doing there, really, while the government was acquiring the land and negotiating the contract and building, and so on.

Sullivan

Who was the guiding light behind - ?

Galt

Jack Locke. Jack Locke talked Dr. [Carlyle Smith] Beals, who was then the Dominion Astronomer, into doing something in radio astronomy - something more than solar work.

Sullivan

That is all that had been done in Canada?

Galt

Up until then solar work, yes. I think John Bolton gave a series of lectures at Ottawa to get the thing (?) for us. I'm not sure whether it was Bolton or Pawsey, I think maybe it was Pawsey. I wasn't in on it. That was before I joined the Observatory but this sort of kindled the interest and it was the appropriate time to start pressing. We got money for a 25 meter telescope and the one building and a staff of two or three to begin with, which within a few years grew to about, I guess the maximum was then about 16 or 17. We have been more or less independent out there, though tied to some group in Ottawa. We have been reasonably independent.

Sullivan

Now you went there in '59?

Galt

Yes. Jack Locke was there for the first three years and then he went back to Ottawa.

Sullivan

And then the first thing that was there was the single dish?

Galt

Yes.

Sullivan

And what was that -

Galt

Well, we had a hydrogen line receiver with just a crystal mixer at first, and then we got an Adler tube paramp which was really very good. I think we're the only people to have used them consistently for a long time. It required very little maintenance, but it wasn't the ultimate in noise temperature. And we made hydrogen maps of a number of regions in the sky around suspected associations. Unfortunately we had only one channel, and we made them over and over again, five different times. It was tedious. Then we got interested in low frequency work with the sunspot minimum coming and we built large low frequency antennas that were - one for 10 MHz and one for 22 MHz, with beamwidths between a degree and a degree and a half, so that we had very high resolution at that frequency.

Sullivan

Well that was the best in the world, wasn't it, that array?

Galt

Yes. All of that hasn't come out yet from the last sunspot minimum, although it's nearly finished.

Sullivan

Was there a loss of interest in the single dish?

Galt

It wasn't so much a loss of interest but we felt that the sunspot minimum wouldn't wait and that we were committed to this other thing. And so we were doing a continuum survey which required very little effort - we were simply doing drift scans all day. We mapped the sky at 1420 [MHz] and made a source list which a number of those regions have been re-observed in the meantime. That was being done during the years we made the low frequency arrays. Then after that we used the telescope for long baseline interferometry and pulsar work.

Sullivan

What got you interested in doing the interferometer as opposed to the single dish? I'm trying to understand why you shifted.

Galt

To the supersynthesis?

Sullivan

No, to the low frequency.

Galt

Oh, that wasn't an interferometer, it was a -

Sullivan

I see.

Galt

They were T-shaped instruments, so we could map the large features as well as the small ones. Well, Carman Costain was the one who pushed that. He had done 38 MHz work at Cambridge and this was one step further on, that was 22 MHz. Later we decided to go all the way and go to 10 MHz as well. So we had two large antennas during sunspot minimum.

Sullivan

Well in fact at such low frequencies what other work had been done besides Reber's classic stuff?

Galt

There's the work in Australia and Tom Clark, who's at Goddard now, had a smaller array at 10 MHz in Boulder. He did his degree work there. And he was able to see well I'm not sure exactly but the 5 or 10 brightest sources only and we were able to actually map the Galactic plane and see the absorption ridges and several hundred point sources.

Sullivan

What was your main goal?

Galt

Well, different people who were in it had different goals. Initially it was simply to map the galactic background looking for well, to get further data on the spectrum of the background to see if the halo and the plane were different spectra, and also to look for the HII absorption along the plane, which appears in emission at high frequencies. This is one way of seeing HII regions that hasn't been fully exploited yet until we had done this. And actually the results from that have been useful in interpreting pulsar dispersion measures to change them into distances as well. And then there was the other interest in simply getting more points on the spectra of more radio sources to try and see if there was a particular characteristic for a quasar. For instance, one knew that 3C84 had turned over by the time you got to 38 megacycles and was heading down. Now we wanted to know whether this was a characteristic of quasars or whether we would ever see the turnover. In most cases we didn't see it turn over, the spectrum is still going up to 10 MHz.

Sullivan

How many sources did you get at the low frequencies?

Galt

A few more than a hundred at 10 MHz, and depending on how far down to the noise you could go, oh, several hundred at 22 MHz. I think 200 of them ware published and the rest of it is being worked on.

Sullivan

Now one thing I'm interested in is the first VLBI which was done in Canada and which was between Penticton and Algonquin. Was it the 120 foot dish actually or another dish?

Galt

Forty-six meter dish at Algonquin. The thing was done in several stages. The first stage was done entirely in Algonquin Park with the 46-meter dish and almost right beside it a much smaller dish, about 20 meters, and they were connected up as an interferometer, but with completely independent tape recorders and so on. They were operated as an analog interferometer in real time and then simultaneously records were made and when the recordings were played back in synchronism the actual noise on the record was the same on the two, so that we were then convinced that the technique would work. And there was nothing intrinsic in the experiment which would be worse if we had moved further away.

Sullivan

Now who is 'we' and when is this taking place?

Galt

It would be about '67, I guess.

Sullivan

Oh it's that late, this first part?

Galt

Yes. '66, maybe.

Sullivan

OK, this is a little bit past the deadline but nevertheless I'd like to hear about it.

Galt

The main people behind that well the names are on the papers, but Alan Yen in Toronto, and Herb Gush who was in the Physics Department at Toronto and helped push it in the initial stages but didn't continue with it. Jack Locke, Norm Broten and myself; and [Robin] Bob Chisholm who has since died [who was] at Queen's.

Sullivan

Now what was the philosophy of doing it in analog fashion as opposed to the digital fashion that was done in the United States?

Galt

Well I think the philosophy was simply that one, the technology had already been developed to do the experiment at 4 MHz bandwidth by the television industry. Tape recorders had been made that could maintain the necessary time base stability, just for the entertainment industry, and we felt there was a bare minimum amount of extra equipment required. And in fact we got beat-up old tape recorders that were discarded by the CBC and we simply beat them into working, and used them for a number of years before they were replaced with anything better. You always win in bandwidth and we could then go to a much lower flux level. There were no large costs in computing to do the correlating because the correlating of it is analog it came out automatically. One could still make corrections in playback for any mistakes you made in observing, depending on - well, some mistakes. There's been a lot more work done with the digital systems, but this is partly because more people were working in the States on it. We get bandwidth much more easily in the analog fashion.

Sullivan

OK, to go back, you said that once you had proved it would work on a short baseline then it was just the next jump to transcontinental?

Galt

Yes and no. Incidentally, there is a historical article about this a little article by McKinley who is two or three stages up above the soldering iron in the Research Council. It's in Science Forum, a Canadian publication.

Sullivan

When?

Galt

It's about issue number 6. The publication only began in the late 1960's.

Sullivan

And this is the history of VLBI in Canada?

Galt

Yes, it's D.W.R.McKinley [Note added in 2015: Science Forum, vol.1, pp. 21-24 (1968)] and he tells a few little anecdotes including this one that when we decided that the thing would work with the two telescopes in the same backyard, we had the option of going a moderate distance away or going clear across the continent. And we thought we'd be adventurous and we went clear across the continent but when we played the tapes we didn't get anything and we were quite discouraged. So we decided we had been overly ambitious or - maybe - that the sources were all resolved. So we brought all the apparatus back from Penticton to Ottawa and we had a very modest baseline of just a hundred kilometers or so between Ottawa and Algonquin, and a smaller telescope, too. And we saw fringes on every source we looked at. So while we were doing these somebody well, the people got proficient in finding fringes in the noise and all the odds and ends you have to do. And then for fun they played back a tape from a pair of tapes from Ottawa and Algonquin and sure enough there were fringes on that. So we didn't really have - no from Penticton-Algonquin so we really didn't have to bring all the apparatus back.

Sullivan

It was just a matter of learning the technique.

Galt

It was partly practice and there were two or three little things like oh, a double beam oscilloscope that had a two microsecond offset that nobody knew about.

Sullivan

Little things like that, yes. This reminds me of an experience with water vapor VLBI, as you know, the fine art, searching for fringes. OK, is there anything else prior to '65 or so that is of significance to Penticton?

Galt

Probably not (laughs).

Sullivan

Who is the best person to talk to about the Algonquin Park development?

Galt

The person in charge now is Jack Locke, but Jack didn't come on the scene in Algonquin until a bit later. Norm Broten, I guess. He knows enough about it. And Bill Cummings who is an antenna engineer, and had a lot to do with it in the early days.

Sullivan

And Covington should definitely be -

Galt

Yes, although mainly for the solar. He never had too much interest in the 46-meter dish.

Sullivan

Yes, I'm thinking mainly what the Canadian radio astronomy. OK, well thank you very much. That ends the interview with John Galt on June 6th 1973 at Onsala.


Modified on Tuesday, 10-Nov-2015 13:13:58 EST by Ellen Bouton, Archivist (Questions or feedback)