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Author Topic: 2m beam on top of 6m beam - minimum distance?  (Read 613 times)
NZ5N
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« on: May 28, 2007, 12:10:21 PM »

I'm in Europe without my books and forgot how much distance I need to keep between my 6m and 2m beam.  Would someone please remind me?
Thanks,
Bill NZ5N/OM9ACA
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AA4PB
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« Reply #1 on: May 28, 2007, 05:17:58 PM »

At least 1/2 wavelength on 2M or 3.25-feet.
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KC2RRE
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« Reply #2 on: June 15, 2007, 09:41:19 AM »

Would this be any different if the antennas were polarized differently? i.e. 2m/70cm yagi vertical at the top of the mast and a 6m horizontal further down?

(I'm guessing yes, and would assume there's very little interaction between them)

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EI8DRB
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« Reply #3 on: June 20, 2007, 03:42:43 AM »

Surely 1/2 wavelength at the lower of the two frequencies? In other words, the 6m, half of which would be 3m.
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NZ5N
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« Reply #4 on: June 20, 2007, 04:43:28 PM »

I did a search of the forums and it seems there are numerous opinions, such as:
* 1/2 wave of the higher freq
* 1/2 wave of the lower freq
* 1/2 the boom length of the shorter boom
* 3 feet
* 5 feet
* manufacturer recommended stacking distance

I do not believe AA4PB's answer was a typo, as he has given this same answer several times.

73,
Bill
NZ5N/OM9ACA
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AA4PB
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« Reply #5 on: June 20, 2007, 05:59:10 PM »

I believe that 1/2 wavelength of the *higher* frequency is the general rule of thumb. Its related to the amount of interaction between the two antennas operated on two widely separated frequencies (i.e. different ham bands) and there is no absolute number. Closer equals more interaction, farther equals less. It doesn't mean that a foot or two closer than 1/2 wavelength will suddenly make the antennas stop working.

Stacking distance for antennas on different bands (done to minimize interaction) is quite different than stacking two antennas of the same band and phasing the feeds to increase gain. Some of the responses you found appear to have confused the two.
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K9MRD
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« Reply #6 on: June 20, 2007, 08:13:21 PM »

FWIW, the capture area (aperture) of the higher frequency antenna determines ideal spacing. The point is to keep the lower frequency antenna out of the higher frequency antenna's capture area. If the lower frequency antenna is within the capture area of the higher frequency antenna, the higher frequency antenna's pattern will distort.

This procedure will put the 2 meter antenna within the 6 meter antenna's capture area, but since the 2 meter antenna is smaller wavelength wise compared to 6 meters, it will have less effect on the 6 meter beam pattern than if the roles were reversed.

There is different minimum optimal spacing distance for every antenna dependent upon its design because  capture area changes depending on antenna design, i.e. number of elements, boom length, etc. all change the aperture or capture area.

To determine the ideal minimum spacing, consult the 2-meter antenna manufacture and find the heigth of the vertical capture area. Minimum spacing is then 1/2 of the vertical capture height.

This got a little lengthy, but I hope it sheds a little light on the topic.
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