A rare book indeed.
http://used.addall.com/SuperRare/submitRare.cgi?isbn=0070353921&order=PRICE&ordering
I started at Wiki and used the reference links to find this. or simply search for "john kraus helical antenna
We seem to have got our wires crossed here. It was not Kraus's book on Radio Astronomy I wanted, but a paper Kraus wrote. I can't recall the title of the paper. The paper is referenced in Kraus's book on Antenna Engineering, as a footnote in the chapter on Helical Antennas. But I don't have his book with me just now, so I don't have the title of the IRE paper.
But I found a 1977 paper "A 50-Ohm Input Impedance for Helical Beam Antennas" as an "Antenna Design Note"
http://ieeexplore.ieee.org/xpl/arti...mber=1141687&contentType=Journals+&+Magazines
which seems as though it covers what I was expecting in the sixty-odd year old IRE paper, which I can't locate. The strange thing is, this IEEE paper does not reference the older IRE one. In fact, there are no references dated later than 1948, though the manuscript was submitted in 1976. I'm wondering if this IEEE "Antenna Design Note" is just a reprint of the older IRE paper, though it never says that. But it's odd there are no references later than 1948. Most people writing a paper would have at least one reference to a paper written in the last 29 years.
Anyway, his basic method in the 1977 IEEE paper is to put a bit of sheet metal on the bottom quarter turn of the helix. This is placed near the ground, so makes a lower impedance transmission line, to act as a quarter wave matching transformer. He says the dimensions and adjustments are not critical, but by way of example says he used 70 mm wide strip for a helix which used 13 mm tubing on the 1.3 metre band.
I thought from reading the Kraus Antennas book, which as I say I don't have in front of me, the tube was flattened. Clearly you could make a wider (low impedance) transmission line by flattening the round tube, but it seems in this paper he made it wider by solding sheet metal to it.
BTW, you provided a link to copies of Kraus's book on Radio Astronomy. As I said, that was not what I was looking for, but you caused me to search for the Radio Asonomy book on Amazon UK, where I see a copy for £3.09 (~ $5). I decided it was too good an oppotunity to miss, so I bought a copy! I don't actualy have much interest in radio astronomy, but you never know, reading a book by Kraus could excite an interest. I used to be interested in astronomy, and have always been interested in radio. The only thing is, I have a finite lifetime and will never finish all the projects I started. I don't fancy taking on one of building a radio telescope. If I did, it would not be as large as the one Kraus built!