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1-3 of 3 messages
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Page 1 of 1
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Quad Building
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Reply
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by KO1D on October 19, 2009
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OK so building a monoband quad is straight forward; been there done that got the t-shirt.
Building a multi-band is maybe not so straight forward?
I am looking at building a 6-2-440 (maybe including 10m and/or 220 on it as well) quad for use at home. I am thinking 4 elements on 6 may be my max length. That should give me an average and totally acceptable to the XYL antenna on the roof. It'd also give me plenty to work with on 2 and 440 for some rather elementary and entry level weak signal work.
Materials would be 12 or 14 g wire and PVC. Feedlines would depend on the budget but ideally LMR 400 or 9913 on the high bands and maybe for 6m cheap out with RG 8 until more cashola appears. I am thinking all the pig tails would be RG58 size cabling cut long enough to allow the rotor to do its job. I would then barrel connect from the pig tails into the primary cable back to the station in the garage 2 floors below.
What I am wondering is when I am drawing this up on paper what interaction is there when going from a mono- to multi-band quad that I have to worry about? I realize that testing once erect is a must but I'd rather not end up short of wire by a foot and rebuilding it or vice-versa if possible. Trimming an inch or two would suffice tyvm :0)
Also if there are issues combining any of the above bands into a single quad please let me know as well. I can always adjust as necessary.
Thanks in advance.
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RE: Quad Building
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Reply
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by WB6BYU on October 19, 2009
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Shouldn't be a problem with 6m anyway. I'd recommend
W4RNL's quad calculator - I've built a couple of his
designs by formula and they work very well (SWR, pattern,
and measured gain) without any trimming.
Adding 2m may not be quite as simple, however, to the
extent that the 6m elements may be close to resonance,
but it may work. You'll also have to find some reliable
longer quad designs - I've seen a few around, but some of
the standard calculator formulas don't account for the wire
diameter, so can't be trusted. The 2m elements may mess
up the 70cm pattern as well - I'd suggest you model it
first. Start with a good design for each band, then add
the 6m and 2m models together and optimize them. If you
have problems trying all three antennas at once, you can
leave off the 6m antenna when optimizing the 2m and 70cm
ones.
You may find, however, that a long yagi for 432 works
better than a quad.
Here are some of the W4RNL pages that may be of interest
(but you have to register for free to read the site):
http://www.cebik.com/content/a10/quad/2mq.html
http://www.cebik.com/content/a10/vhf/qvy.html
http://www.cebik.com/content/a10/vhf/qy.html
http://www.cebik.com/content/a10/trans/ant-design.html
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RE: Quad Building
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Reply
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by WB6BYU on October 23, 2009
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OK, I took an existing 2m 5-element W3GNR design, added an
element, and stretched it to 106" boom length. It had
about 14.5 dBi gain and 19 dB F/B, with a 50 ohm input
impedance at 144.5 MHz.
Then I added a W4RNL 3-element 6m quad (or approximation
thereof) with a 92" boom length around it. I didn't try
to put the elements on the same spreaders.
The 2m quad dropped to about 11dBi gain - a loss of 1.5dB.
The F/B actually improved to 23dB. The impedance moved
to 63 ohms @ 145.25 MHZ, but lengthen the last director
moved it back to where it had been before. There didn't
appear to be much detuning of the 6m quad.
That's not to say that these are the optimum designs to
use, just that I had the models handy so I used them to
see what happened.
The problem is that the 6m quad is close to resonance on
2m in the 3 wavelength mode. But you may be able to
tweak the element lengths and recover some of the lost
gain, and otherwise performance wasn't that bad. If
you just put up the two antennas without any corrections
they would still work.
I would strongly suggest modeling the antennas in a
program such as EZNEC, however, as it makes antenna
adjustment much simpler. It is a fairly large model -
I'm using around 350 segments and it still complains
that I need more of them for the 6m wires. (The program
maximum is 500 for this version.) Model each antenna
individually to get the gain, pattern, and SWR where
you want them, then combine the two and make final
adjustments. Then you can just build the antenna and
connect the feedline. (Trying to adjust quad elements
one at a time in the real world is very difficult, as
the change that any one element makes to the pattern
may be difficult to measure. Different elements affect
the pattern, SWR, and gain in various ways, which is
one of the reasons for experimenting with the basic
model first to get a feel for how it responds to changes.)
Good luck!
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