This would be a design nightmare. You might want to consider a simpler
approach. With three verticals in an equilateral triangle layout, and proper
switching, you could build a parasitic array with at least 6 beam headings.
By driving one element, shorting another to create a parasitic and opening the
third to make it inert, you can make a number of 2el beams with just a couple
relays at each base. You would have to place the relays in the housing so that
the connection between matching network could be bypassed for the open and
shorted conditions.
If you needed more than six headings, you could use both parasitics at the same
time as reflectors, giving three more directions... but this adds to the
complexity. Of course, you would have to setup a bunch of custom antenna
lengths and daisy chain the controllers.
A far simpler, higher gain, but more expensive approach would be to use 5
verticals in a box configuration with one in each corner and one in the center.
This would produce a 3 element beam in four directions firing diagonally, with
no feed switching since the center element would always be fed. The "driven"
element would use stock SteppIR settings, each "parasitic" element would have
custom settings for director and reflector lengths, plus a relay to "open" the
element.
Keep in mind that the H-plane pattern is much broader than the E-plane pattern,
so four directions would probably be OK if the centers of the lobes can be
placed on important directions such as Europe or Japan. The box wouldn't have
to be square, so there is some room for adjustment of the lobe headings.
You could also get 8 headings by using two reflectors and two directors at a
time to fire off the sides of the box, with reduced performance, but this adds
to the complexity and probably wouldn't be necessary.
I had a 160/80 (using switched loading coil on 160) version of this design at a
contest station I had out in the country years ago and it worked great.
73,
Larry N8LP
----- Original Message -----
From: Jim Lux
To: skip ; towertalk@contesting.com
Sent: Sunday, September 26, 2004 9:14 AM
Subject: Re: [TowerTalk] SteppIR Vert
----- Original Message -----
From: "skip" <k3cc@fast.net>
To: <towertalk@contesting.com>
Sent: Saturday, September 25, 2004 9:17 AM
Subject: [TowerTalk] SteppIR Vert
> I've just ordered a SteppIR Big Vertical 40 thru 6 meters.
>
> My question is would it be feasible to make a 4 square out of 4 of them
> using a 1/4 wavelength spacing on 40 meters ???
>
> This would be 1/2 wave on 20 and full wave on 10
>
> If their were separate switch phasing lines, relay switched, and a phasing
> box to switch the direction.
>
> I have not yet calculated the lead/lag as yet for phase angles.
>
> Has anyone built or thought about a multiband 4 square ???
>
> Or is this just wishful thinking ????
>
> de Skip K3CC
I've thought quite a lot about multiband phased arrays using tunable
elements such as the SteppIR. Here's the tricky parts:
1) 1/4 wave spacing on 40 might not be what you want. You need to choose a
spacing that works out for all bands, because spacings like 1 wavelength
tend to be less useful than you might think (you get lots of lobes and
nulls, and it's difficult to control exactly where they'll wind up). But,
see later...
2) The mutual impedance will be different on the different bands (generally,
speaking, less on the higher bands, because the elements are farther apart
(in terms of wavelength), which means that your phasing networks will be
quite a bit different for each band.
3) You can use the variable length feature to help with the phasing (because
you can make the element a bit longer or shorter to add L or C to the
feedpoint impedance)
4) A square arrangement, while easy to do calculations on paper for, may not
be the optimum arrangement for you. You need to get a map out and figure out
where you want to form beams and/or nulls. It might well be that a straight
line arrangement might work out better.
5) I think the true value of a phased array is not in forming the beam, but
in forming a null. An array with 4 elements spaced a reasonable distance
apart isn't going to have a huge amount of gain, but can potentially form
very useful nulls and "low response" areas to cut down on signals coming
from areas where you don't want to talk to. This, however, requires a
substantially more sophisticated approach to the phasing network control
(the networks are the same, but figuring out the Ls and Cs is non-trivial)
If you want to fool with phase calculations with various arrangements of
elements, I've got an excel spreadsheet I can send you that allows you to
specify the x,y position of your elements, as well as the phase and
magnitude of the current in the element, and it calculates the horizontal
pattern. It can also use Excel's optimizer to try and find the currents that
produce a pattern as close as possible to what you desire. (Of course, that
leaves the hard part of the feed networks).
Jim, W6RMK
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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