Dave wrote:

Quck question, Roy,

Would it matter if I "separated" the whips electrically with, say, 55 feet
of coax? (That's approx the length I get for RG-174 coax, which is
something like 1/8" in diameter, with a velocity vactor of .66 and working
with 9 MHz.) Just a thought, but I don't know whether it has any merit or
not. And I am thinking I could adjust that "length" with an RLC circuit
through which I sort of "tune" it. What say you? Is this line of thought
worth persuing? Or would wiggling he whips still throw everything off?

And I do seem to have a fair abount of patience with this sort of thing.
Been working on the current project for about 2 years, had it working on and
off, taking it apart occasionally to implement some new retrofit or
engineering change. I am on disability, and have nothing but time on my
hands.

Thanks for any feedback...

You can answer most of your questions by modeling it with EZNEC. The
free demo program available from http://eznec.com is perfectly adequate
for the job. After going through the "Test Drive" tutorial in the
manual, I suggest that you take a look at the d_Cardioid.ez example file
to see how you can model an array with an ideal feed system. What you
should do is model your array in a similar manner, with two perfect
current sources. With the sources equal in magnitude and 180 degrees out
of phase, you'll get a bidirectional pattern, and it won't be sensitive
to frequency or element spacing. But then see what happens when you
change the phase and/or magnitude of one of the sources just slightly,
to simulate what any real phasing network would do. What happens to the
pattern? Look at the feedpoint impedances at various frequencies, and
see if you can figure out how you'll make a network to deliver the
correctly phased currents into those impedances. Another thing you can
do is try phasing them for a unidirectional pattern by giving the
sources a relative phase angle of 180 degrees minus the electrical
spacing of the elements (which of course will be different at each
frequency). You can get a nice looking pattern, but you'll find it
extremely sensitive to frequency and element spacing.

EZNEC will give you the opportunity to turn some of that available time
into an educational experience. I guarantee you'll learn a lot in the
process. If you want to learn even more about phased arrays, see Chapter
8 of the _ARRL Antenna Book_. The phased array section was completely
rewritten and updated for the latest (21st) edition.

Roy Lewallen, W7EL