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Author Topic: hanging wire antenna in inverted fashion from tower  (Read 1351 times)
KB2HUK
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Posts: 164




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« on: July 13, 2010, 08:40:28 PM »

Hello all you tech types :>)  I am thinking of hanging a OCF wire antenna in a inverted V fashion from the last section of my 60 foot aluminium tower .  My question is this does the tower interact with the antenna if so should I hang the wire antenna from a coax arm of some sort to remove it a distance from the tower ?  is hanging the feed point of a OCF 160 mtr multi band antenna at 55 feet high enough to see results on 160 mtrs ?  are there any rules to follow when hanging a wire from the tower in this fashion?  Would this be better than hanging it as a standard flat top ?  thanks for all the answers in advance  73s  de  kb2huk  John
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KI4SDY
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« Reply #1 on: July 13, 2010, 08:56:50 PM »

If you can get it the same 55 feet up, I would hang it as a flat top. If you like the performance in those directions, buy another later and hang it in the opposite direction with a switch box connected to the two. The best of both worlds with no rotor expenses or worries.  Grin
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N4CR
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« Reply #2 on: July 13, 2010, 10:04:23 PM »

Yes, of course any metal in the vicinity will create interaction. Any amount that you stand it off from the tower with a yard arm will lessen the interaction with the tower. Just a guess, but I believe a foot or two would be adequate to get the feed point away from the tower. Of course, more is better.

I use the largest powder coated shelf brackets from the local Home Depot store. The ones that have a 45 degree diagonal brace welded in. I've had one up for several years with no indication of rust. They won't last forever though. Galvanized or anodized aluminum would be better long term.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
VA7CPC
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« Reply #3 on: July 13, 2010, 11:14:02 PM »

If there's a 1:1 current balun at the dipole antenna feedpoint (as there should be), the electrical potential, halfway between the radiating wires, should be _0_.

The tower shouldn't have much effect.

This would be an interesting modelling problem for EZNEC.

                 Charles
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NE5C
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« Reply #4 on: July 14, 2010, 03:03:32 AM »

Hi John,
Just a hint of an idea that worked for me...I used some plastic Molding which is like 2-sections 2"X1"X6'ft long doubled,(used commercially to frame outside of garage doors) I screwed the pieces together using the razor sharp hobby or drywall screws.

At 50'ft I inserted this cross ways into the tower, so that about 3ft extends out both sides. I then used 2 hole conduit clamps, which are screwed down holding the horizontal brace to the tower stand tubing so it will stay put. On each extended side, out on the ends, I added some very small stainless pulleys which I then use a braided nylon parachute chord down to the base of the tower. This gives me the ability to raise and lower wire antennas so easily, yet works great as a poor boy...simple stand off, to keep the antenna slightly away from the tower.

Hey whatever works...73 and God Bless
Jerry N5JFJ

 
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W5LZ
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« Reply #5 on: July 14, 2010, 06:49:20 AM »

Will that tower affect that antenna?  Sure, to some extent, which may or may not be 'bad'.  How do you tell?  Try it and see.  Don't like how it acts?  Change it.  That works the same no matter how the antenna is 'hung', straight, inverted, whatever.  Perpendicular to the tower is 'better' than parallel to the tower, in most cases.  And since every installation is different, what might work just dandy for me may not work worth a hoot for you.
Paul
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N4CR
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« Reply #6 on: July 14, 2010, 01:02:56 PM »

If there's a 1:1 current balun at the dipole antenna feedpoint (as there should be), the electrical potential, halfway between the radiating wires, should be _0_.

The only way the electrical potential at the feed point could be zero is if there is no current flowing. I bet that doesn't transmit worth a darn. Besides we're talking about a radio and a magnetic wave and the feed point is where these are the strongest.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
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