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Author Topic: stacked  (Read 920 times)
KJ7YY
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Posts: 13




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« on: October 23, 2012, 03:45:09 PM »

I am in the process of putting up a 3 element 17 meter beam.  I have that figured out, I think.  What I want to do is put a 12 meter rotatable dipole above the 17 meter antenna.  I have read the .2 wavelength of the higher freq. is OK for separation.  Might I place the dipole 90 degrees off the beam?  Any benefit from this?  Both antennas are to be resonant in the middle of the band.  I hope that is.  All advice appreciated.  John, KJ7YY
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WB2WIK
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Posts: 20603




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« Reply #1 on: October 23, 2012, 03:57:09 PM »

I'd be very temped to put the 12m rotary dipole right on the same boom as the 3L 17m beam (interlaced).

Check out how Force-12 does this with the XR-5 and some other models.

You can model the results and play around with spacing for minimum interaction.

OTOH if the 17m beam is still on the ground, I'd be really temped to make it a dual-band 3L beam, using 12m traps!  One antenna instead of two, with gain on 12m.
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WX7G
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Posts: 6080




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« Reply #2 on: October 24, 2012, 06:28:02 AM »

I ran an EZNEC simulation of an 18 MHz dipole and a 25 MHz dipole.

When the dipoles are aligned there is interaction even at 1/4 wavelength spacing. They can be returned.

When the dipoles are at a right angle there is no interaction even at a spacing of 1 ft. In your proposed installation, with a beam and dipole mounted at a right angle, the beam will not be detuned but the dipole will be detuned by the beam boom. It is easier to retune a dipole element than it is to retune a dipole, a beam driven element and possibly the director and reflector. I like your idea of mounting the dipole and beam at a right angle.
« Last Edit: October 24, 2012, 06:31:48 AM by WX7G » Logged
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