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Author Topic: Two antennas near each other question  (Read 975 times)
N4NOO
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Posts: 106




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« on: December 07, 2012, 08:56:36 AM »

I have an inverted-L that runs from the back of the house (about 30 feet high) to a tree about 100 feet away at the back of the yard (about 65 feet high).  I am going to place a flag pole antenna in the middle of the yard.  The inverted-L will be offset about 10 feet to the South and about 5 to 10 feet higher than the vertical. Will there be enough interaction between these two antennas to worry about?
« Last Edit: December 07, 2012, 09:05:12 AM by N4NOO » Logged
WX7G
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Posts: 6219




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« Reply #1 on: December 07, 2012, 09:09:36 AM »

It depends on the frequency and how the undriven antenna is terminated. Given these parameters it is a simple matter to model using NEC.

Maximum interaction will result in azimuth pattern distortion.
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N5CEY
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Posts: 3




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« Reply #2 on: December 07, 2012, 09:58:03 AM »

I put up a 40 meter dipole running almost over the top of my 6btv vertical. Couldn't get the dipole to resonate worth a darn till I moved it about 10 feet to the side of the 6btv. It kept giving me double swr dips on my analyzer and swr was always above 2.5:1 till I moved it. It was only about 5 ft above the vertical.
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KC4MOP
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Posts: 759




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« Reply #3 on: December 07, 2012, 03:40:24 PM »

The separation is not too critical...30 feet or so is ok....Do not terminate the unused antenna. It will interact or de-tune the active antenna. The biggest bad is if the not used antenna is terminated into a radio the antenna you are transmitting can transfer up to 50 watts right into the front end of the un-used antenna/Ham radio transceiver.
I have a big knife switch on my dipole. If I am using the vertical which is almost under the dipole. I flip the knife switch to disconnect from the tuner.
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K4SAV
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Posts: 1850




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« Reply #4 on: December 08, 2012, 06:53:31 AM »

It depends on the operating frequency, location of the antennas relative to each other, detailed description of the antennas including any loading coils, traps or matching networks, length and type of the transmission lines, and termination of those lines at the rig end.  Without that information, everything else is just a guess.

Jerry, K4SAV
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