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Author Topic: Rotatable Dipole vs. Wire Vertical  (Read 4850 times)
AF3Y
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Posts: 3700




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« on: August 09, 2012, 04:46:05 PM »

I have permission from HOA to put up a 30' crankup tower (Good) but no beam antenna (Not good!) . There is one other tower in the development here and he is up 30' with a rotatable 3 band dipole.

So, I can duplicate his tower and antenna and I am wondering if its going to be worth the $ and sweat to get this in the air vs. the S-9 31' wire in fibreglass vertical I am using here now. The S-9 is very noisy, and the manufactured homes here are darn near on top of each other (typical 55+ Fla. retirement community) which does not help things any. Trying to work a weak DX signal here (like Spratly today) requires me to use the pre-amp, etc. and that brings up the noise level to where the DX is damned near un-copyable. GRRR Angry

Cost for a crankup Alumatower and the Cushcraft dipole plus installation is going to be 3 grand+.  I dont mind spending it, IF I get good great results vs the vertical hi.  I dont expect miracles, but would like a quieter receive. I have QRO in the shack, and dont have trouble working DX, WHEN I can HEAR it. Roll Eyes.

Comments??  Thanks in advance, 73, Gene AF3Y
« Last Edit: August 09, 2012, 04:48:06 PM by AF3Y » Logged
KI4SDY
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Posts: 1452




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« Reply #1 on: August 09, 2012, 07:22:44 PM »

If you have any tall trees or can install poles, why don't you try opposing doublet dipoles running North/South and East/West, using a tuner and switch box. That will inexpensively keep your noise level down and your performance up. Think of the money you will save!  Grin
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W5DXP
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« Reply #2 on: August 09, 2012, 07:53:45 PM »

At my last QTH, the horizontal dipoles were about 2 S-units quieter than the verticals. A rotatable dipole is definitely worth the effort. However, my 40' tower cost me ~$250.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K3STX
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« Reply #3 on: August 09, 2012, 07:58:26 PM »

Go for the tower. Maybe over time the powers that be will allow a small beam.

paul
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WA8FOZ
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« Reply #4 on: August 09, 2012, 08:23:06 PM »

Quote
Cost for a crankup Alumatower and the Cushcraft dipole plus installation is going to be 3 grand+.  I dont mind spending it, IF I get good great results vs the vertical hi.  I dont expect miracles, but would like a quieter receive. I have QRO in the shack, and dont have trouble working DX, WHEN I can HEAR it.

Go for it. You will be very impressed with the difference. You will get some relief from local vertically-polarized noise, gain over the vertical, and the ability to null out interference and noise.  On transmit, likely a more efficient radiator (especially if you don't use LOTS of radials) and a much higher elevation - the vertical would be radiating much of its RF into the buildings.

Can you consider a hex beam? Not too obtrusive, and five-band coverage is possible. But even the dipole will be good. And you can hang a fine-wire inverted-V for the lower bands from the tower too.
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KF6ABU
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« Reply #5 on: August 10, 2012, 02:24:57 AM »

I wouldnt spend much money for a dipole at 30ft...

Id much rather have a hygain AV-640 About 10ft up (will need guying, has its own counter poise, and works great)

If you want to put 3 vertical "poles", you can do phased 20m vertical dipoles in 32ish feet across. coax goes to the center support. Zero five and other companies make telescoping aluminum vertical dipoles. That would work better on 20 than the dipole at 30ft, or a good vertical.  Then put the AV-640 in a corver. If you really wanted a rotateable dipole at 30ft, id just use a rohn push up pole and guy it, rotator at the top. at least your not spending too much on a rotateable dipole at 30ft.

I use the Wellbrook ALA1530S+ on a tv rotator for 80/40/30 RX. Its far superior to my steppir vertical for RX. There is another one thats probably exactly the same called a pixie or something from another company.
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M6GOM
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« Reply #6 on: August 10, 2012, 03:27:59 AM »

A dipole is a simple antenna so why not build one out of scrap wire to test before spending a load of money? Put it up as an inverted V with the center at 30ft or as near as you can get. Then do some A/B testing with the vertical, remembering that you need to be comparing signal strengths to stations that are broadside to the dipole so if your dipole runs N/S, you need to look at the signal strengths E/W.

I've compared my 75ft long inverted L that has 25ft vertical to my 5 band dipole at 30ft and the dipole at its worst is as good as the inverted L at its best. And bear in mind my inverted L has lobes with several dB of gain which your vertical won't have.
« Last Edit: August 10, 2012, 03:31:15 AM by M6GOM » Logged
KC4MOP
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« Reply #7 on: August 10, 2012, 04:13:17 AM »

It sounds like you pick the lesser evil. The rotateable dipole will give you a little directional advantage, better than a fixed dipole.
Remember the RF rules. 1/2 wavelength high dipole a particular band is when you can talk about North and South, East and West. So, for 40M you would have to have a dipole, or whatever, 69 feet in the air to notice any direction when rotating. This is from the antenna books.
A Yagi is a little different. But he cannot erect a Yagi. A Yagi is minimally happy at 30 feet and will show a front and back ratio. A yagi is best at 60 feet.

You will just start to notice directions on 40M..........20M and up will be goodness.

Guys, he doesn't have much room at all for a decent dipole on the ground. Even a vertical on the ground will not be happy with the crowded conditions and Gene is complaining about noise in his receive. No matter what we Amateur radio guys put up for antennas, unless you have $50,000, is going to be a compromise to what is needed in the real RF world.

Gene talk to the other Ham and copy his installation. Ask if you can sit in his shack and let you operate on your favorite bands and compare receive noise at his QTH and your system.

Fred
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K2MK
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Posts: 389




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« Reply #8 on: August 10, 2012, 05:49:37 AM »

Just do it while you have the approval. If that other guy moves you might not be able to get approval in the future. Who's to say you couldn't add a 10 foot mast to the tower.

If you can keep the vertical then you can do some switching inside the shack and pick and choose which antenna you use to transmit and which to receive.

73,
Mike K2MK
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KC7YE
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Posts: 93




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« Reply #9 on: August 10, 2012, 06:45:14 AM »

Due to storm damage in the early 80's used my salvaged tribander driven element on 30' US tubular tower until 2006 when sold prior to move to condo. Looked a little funny with bent tubing but hey, it worked and was much better then the 4BTV. No hope now in condo.
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KC4MOP
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Posts: 729




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« Reply #10 on: August 11, 2012, 03:42:56 AM »

Due to storm damage in the early 80's used my salvaged tribander driven element on 30' US tubular tower until 2006 when sold prior to move to condo. Looked a little funny with bent tubing but hey, it worked and was much better then the 4BTV. No hope now in condo.
Spring for one of those MFJ magnetic loop antennas. They are pretty nice for barefoot operation on the upper bands-------20-10M.
Fred
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WA4FNG
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Posts: 162




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« Reply #11 on: August 11, 2012, 07:25:09 PM »

Have you considered a HyTower vertical?
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KD2CJJ
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Posts: 369




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« Reply #12 on: August 16, 2012, 06:51:35 AM »

You make very valid points and why I also abandoned the idea of going with a vertical - Im in a noisy environment and I can not lay a half way decent radial system... BUT I know I can get  rotatable dipole up on my roof above 30 feet --- One other ham on the boards made also an excellent point in focusing me on what I was trying to do - Unfortunately I was trying to do everything but he shifted my though into what are my priorities -

10 - 20 Meter is my priority right now
40 Meter is a future though
I dont have to just have 1 antenna...

My strategy is to go with a rotatable dipole for 10 - 20 meter
End Fed for 40Meter which I can slope from 40 down to about 30 feet (tree accross my yard to the same mast that will be holding my rotatable dipole)...

I suspect this will kick a$$ over what I have now (Fan Dipole 22 feet against my house slanted towards my fence with an apex of 60 degrees)...




It sounds like you pick the lesser evil. The rotateable dipole will give you a little directional advantage, better than a fixed dipole.
Remember the RF rules. 1/2 wavelength high dipole a particular band is when you can talk about North and South, East and West. So, for 40M you would have to have a dipole, or whatever, 69 feet in the air to notice any direction when rotating. This is from the antenna books.
A Yagi is a little different. But he cannot erect a Yagi. A Yagi is minimally happy at 30 feet and will show a front and back ratio. A yagi is best at 60 feet.

You will just start to notice directions on 40M..........20M and up will be goodness.

Guys, he doesn't have much room at all for a decent dipole on the ground. Even a vertical on the ground will not be happy with the crowded conditions and Gene is complaining about noise in his receive. No matter what we Amateur radio guys put up for antennas, unless you have $50,000, is going to be a compromise to what is needed in the real RF world.

Gene talk to the other Ham and copy his installation. Ask if you can sit in his shack and let you operate on your favorite bands and compare receive noise at his QTH and your system.

Fred
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73

Mike
KD2CJJ
W5DXP
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« Reply #13 on: August 16, 2012, 08:11:25 AM »

10 - 20 Meter is my priority right now. 40 Meter is a future though.

Here is an old WorldRadio article about a rotatable dipole for 40m-10m operation. It is almost 3/8WL on 40m and almost an EDZ on 10m. It has a multi-lobbed pattern on 6m.

http://www.w5dxp.com/rotdip.htm
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K4RVN
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Posts: 758




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« Reply #14 on: August 17, 2012, 08:06:36 AM »

Gene,
You might show them a photo of the hex beam which only weighs 25 lbs,  can be had with 6 bands,and does not look like a beam.Looks kinda like a clothes line people used in the old days. They take wind well and I am pleased with mine after replacing a three element 5 band Quad. They might let you install a hex since the footprint it presents is rather small compared to a yagi of similar performance.

Frank
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