I've worked on a great many of these types of antenna arrays in the last
35+ years and every one had an impedance of 50 ohms at the individual
element. An odd multiple of a 1/4 wavelength of 75 ohm coax takes it to 100
ohms. When stacking elements two 100 ohm loads in parallel are 50. Then do
it again for four bays, again for eight, etc.
In free space their impedance would be higher, but they are designed to
work only a few inched from a mast pipe and normally the elements are fairly
fat in terms of diameter to length ratio Hence the nominal 50 ohm
impedance.
Another scheme was to use two bays, make the feed line from each bay a
piece of 50 ohm cable, the length being unimportant other than being equal,
and tying them together for 25 ohms. Then a special 35 ohm 1/4 wave piece of
line brought it back to 50 ohms. Two pieces of 75 ohm cable in parallel
would do the same transformation but can be messy to fabricate.
YMMV, though,
73, Al K9SI
<snip>
Judging from the cable and the lengths listed, each
dipole must present a 100 ohm impedence, not 50,
assuming the data is correct.
<snip>
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