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Author Topic: Using 80M GP to support 80M dipole.  (Read 673 times)
ZL1BBW
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Posts: 371




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« on: April 24, 2013, 02:52:31 AM »

If I put a pulley at the top of my 70ft 80m vertical and use it to support the centre of a 80m inverted v is this going to cause any issues with the performance of the GP?

Just thought it would be nice to have the centre of Inv V up nice and high? 

Would probably use open wire line all the way to the shack.

Thanks
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ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
K2DC
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Posts: 1354


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« Reply #1 on: April 24, 2013, 03:03:47 AM »

I suppose you'll never know how much of an impact there is until you try but it doesn't sound like a great idea to me, unless you intend to drop the inverted vee while you're using the vertical.

73,

Don, K2DC
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K3VAT
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Posts: 705




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« Reply #2 on: April 24, 2013, 05:53:16 AM »

If I put a pulley at the top of my 70ft 80m vertical and use it to support the centre of a 80m inverted v is this going to cause any issues with the performance of the GP?
...  Thanks

Most likely. You're planning to place the proposed vee right in the center of the near-field with each leg of the vee a harmonic of the vertical.  When using the vertical, you'll have max voltage at the top of the vertical, right where the vee attaches.  They will interact - how much depends on a number of factors, but like K2DC correctly pointed out "... you'll never know ... until you try it ..."  AND "... unless you intend to drop the vee while using the vertical."

The same principle holds for guying towers.  You break up (or cut to specific lengths) each guy wire by using insulators to prevent the guys from interacting with the antenna's signal.

GL, 73, Rich, K3VAT
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WB6BYU
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Posts: 13149




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« Reply #3 on: April 24, 2013, 06:57:47 AM »

How would you propose to drop the feedline down to the ground without
it running parallel to the GP radiator?  That may cause more interaction than
the dipole itself.

One alternative is to put up a dipole (possibly fed with twinlead) and use it
as both the dipole (when fed in push-pull in the base) and as a vertical
radiator (when the two wires are connected in parallel and fed against
ground.) 

This will have a high-impedance when used as a vertical, which will require some
sort of matching network at the base.  One design I saw used ladder line to feed
the dipole, which stepped up the impedance so it had a high impedance also, then
the same matching network was used for both antenna with just the wires switched
around.
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ZL1BBW
Member

Posts: 371




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« Reply #4 on: April 24, 2013, 12:24:14 PM »

Thanks all, I had thought it was a bad idea, but rather than rule it out, thought I would ask.  Will be trying to get a line over some trees today, that will be the home of the 80m Inv V I hope.  Its going to be a bit of effort to get the GP so dont want to mess it up.
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ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
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