"Roy Lewallen" wrote in message
...
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

Thank you, Roy. Seriously. I've been putting off trying EZNEC out, but
guess it's been long enough. Like you say, time to put some of my spare
time into a serious learning experience. Thank you for that link, too. Now
I have no excuses.

I do appreciate your feedback, and encouragement. Sorry if I was being
lazy. I really don't know why I've been putting it off, but I realize now
that I have.

'preciate it.

Dave

PS: Thanks too for the tip on the latest edition of the ARRL Antenna
Handbook. Now I know I need to get that edition, and not an older one.