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Author Topic: Stacking 2 meter & 6 meter square (loops)  (Read 6491 times)
KG6WLS
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Posts: 507




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« on: March 27, 2005, 10:31:12 AM »

 I've made many 2 meter and 6 meter copper square dipoles (K0FF's design) for myself and others in my ham community. They work outstanding! Can't seem to find any info for stacking these antennas.

 Does anyone know what the spacing would be (in feet or inches) for the 2 meter and the 6 meter loops? Do you paralel feed them?

 Any thoughts, suggestions, experiance, links that I may have missed, or constructive criticisim would be greatly appreciated. I'm ready for it, go ahead.

Thanks in advance & 73
KG6WLS

 
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WA6BFH
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Posts: 646


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« Reply #1 on: March 27, 2005, 10:59:37 AM »

Stacking any antenna to produce gain relates to the ‘aperture size’ of that design antenna as a single unit. What you are trying to accomplish is to nicely combine the two main lobes of each antenna. As an example, you might have two 6 element Yagi beams, one design built on a 20 foot boom, and a different design built on a 24 foot length boom. The aperture ‘gain area’ of these two designs will be different. Their main lobes would look different when plotted (I‘m not suggesting stacking the two different dimension antennas)!

Anyway, the best way to answer your question is to try this against a ‘long baseline’ signal source. I often use distant repeaters to do this. If you can find such a source (you would will probably want the help of another Ham at some distance from your home) here is how to proceed.

Build and mount the antennas about ½ wavelength apart. Check the carrier signal from your test source (if necessary, use a step attenuator to take this signal below AGC cutoff). Move the antennas closer or farther apart by 1/8 wavelength increments, keep track of the tested stacking dimensions, and find the best separation distance for your given aperture size antenna!

73! de John
PS
You can also measure antenna gain by much this same method with a good trustworthy step attenuator!
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WB2WIK
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Posts: 21753




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« Reply #2 on: March 27, 2005, 03:35:18 PM »

Square loops are usually only 1/2 wavelength, like circular halo antennas; as such, their optimum stacking distance (spacing) is only about 1/2 wavelength.   That is, on 2m, about 39 inches between loops, and on 6m, about 112 inches between loops.

You don't just feed them in parallel, you feed them through a phasing harness which feeds the loops in phase but adjusts their overall network impedance back to fifty Ohms.  Usually, this means using an odd number of quarter-waves in coax to feed each antenna.

On 2m, a quarter wave in coax using solid PE dielectric cable is 13.5 inches, for 144.2 MHz.  On 6m, it's 39 inches, for 50.125 MHz.  That assumes *solid dielectric* cable like RG213/U.  For foam dielectric cable, it's about 16 inches for 144.2 MHz and 46 inches for 50.125 MHz.

Since that's not far enough to "reach" the distance between antennas spaced half wave apart, use 3x that distance for the phasing harness (per branch).

WB2WIK/6
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WB2WIK
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« Reply #3 on: March 27, 2005, 03:37:56 PM »

Oops, in reading that post, I realized I didn't mention the phasing lines should be made from 75 Ohm coax, to transform impedance of each square loop up to 100 Ohms (so, when they are combined, they will look like a 50 Ohm load).

Sorry!

The phasing harness should be made from RG59/U, RG6/U, RG11/U or whatever.  Use the smaller lengths for solid dielectric coax, or the longer lengths for "foam" dielectric coax.

WB2WIK/6
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