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Author Topic: A3S at 30 ft vs 20 ft  (Read 1493 times)
KD8IZZ
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Posts: 282




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« on: October 31, 2012, 11:45:33 AM »

I have a Cushcraft A3S at 20 feet, it's near the end of a single length of pipe and use an armstrong rotor. It's pipeclamped to the side of a small barn. It works OK with 150 entities over 4 years.

But I could buy tower, attach it to the barn and get up to 30'. I don't want to use guy wires.

I'm fairly sure that would improve things on 20 meters, but should I expect much for 10 and 15 ?
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AD4U
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Posts: 2179




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« Reply #1 on: October 31, 2012, 11:55:23 AM »

Nobody can guarantee that you will notice a "night and day" increase in antenna performance with that set-up.  But IMO you should notice an improvement in overall performance. 

There are graphs in handbooks showing "take off" angles for antennas at different heights above ground.  GENERALLY the lower the "take off" angle the better the DX performance.  With your antenna at 30 feet you can easily see that you will get a lower "take off" angle on all three bands than you are getting now at 20 feet.

Since 30 feet will approach a 1/2 wavelength on 20 meters, 3/4 wavelength on 15 meters, and one wavelength on 10 meters, the added heighth should be worth the effort.

Dick  AD4U
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KD8IZZ
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Posts: 282




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« Reply #2 on: October 31, 2012, 01:04:44 PM »

The halfwave height on 20 meters should lower the SWR on that band for me. I need to use the autotuner presently.

Right now I can reach Japan on 10 meters from Ohio but only to the big guns. I got 14 JAs in the CQWW contest and almost all have pictures of their monstrous antennas on QRZ. Cheesy

Another question: would the 40 meter dipole attachment for the A3S be useful at 20 feet? (compared to a wire at the same height)
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W8ATA
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« Reply #3 on: October 31, 2012, 06:03:36 PM »

My experience when I had the A3S was when I was able to get it to 38' with some heavy TV tower anchored to the high point of the house  with two feet in concrete and a short mast there was a marked improvement on 20 meters. Just my experience ....your mileage may vary.

73 and best to you,
Russ
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WX7G
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« Reply #4 on: October 31, 2012, 06:52:51 PM »

Let's see what an EZNEC simulation of a 14 MHz dipole up 20' and 30' looks like. At a take-off-angle of 10 degrees (stateside and DX angle) the gain difference is 3.6 dB.
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WB2WIK
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« Reply #5 on: October 31, 2012, 07:12:12 PM »

I have a telescoping tower that can raise or lower my HF beam from 56' down to about 26'.

The difference is, um, remarkable.  There are many stations I can copy just fine with the beam "up" that aren't even there at all with the beam "down."  And I've tried that a lot of times, since it can be raised or lowered in about a minute.

70' is better, though.  I used to have a 70' telescoping tower previously and the difference was more remarkable.
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G3RZP
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« Reply #6 on: November 01, 2012, 03:19:58 AM »

But you can be too high, too! Back in the 1986 Bermuda contest, when running the 5 element monobander at 62 feet, I could 'run' the US west coast, but I had problems with QRM from the East Coast. A G5RV at 30 feet  kept the East Coast at bay, so I was continually switching between them.

A 4ele 10m Yagi at 68 feet was often too high for DX in the caribbean, although fine for the really long haul stuff as the band was opening or closing. But going from 20 to 30 feet will very likely make a difference.
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KD8IZZ
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Posts: 282




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« Reply #7 on: November 01, 2012, 03:54:49 AM »

Thanks everyone. It looks like it's a quorum, the extra 10 feet will noticeably improve my capability.
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WX7G
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« Reply #8 on: November 01, 2012, 07:29:32 AM »

Yes indeed. The gain difference from 20' to 30' is such that a dipole at 30 ft. could almost beat the A3S at 20 ft.
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G3TXQ
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« Reply #9 on: November 01, 2012, 09:19:16 AM »

Take a look at the chart in section 2 here:
http://www.karinya.net/g3txq/hexbeam/height_2/

It shows relative performance vs height for short-haul, medium-haul, and long-haul paths on 10m and 20m.

But remember that sometimes it's worth sacrificing the odd dB of average Forward Gain if it means avoiding an elevation null in the spread of likely arrival angles.

73,
Steve G3TXQ
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N8CBX
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Posts: 164




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« Reply #10 on: November 01, 2012, 04:09:26 PM »

... the extra 10 feet will noticeably improve my capability.
Get it up as high as possible, Ray. That's my suggestion.
Jan N8CBX
73
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Dayton Ohio - The Birthplace of Aviation
KD8IZZ
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Posts: 282




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« Reply #11 on: November 05, 2012, 09:42:12 AM »

Thanks. I need to duplicate those calculations for a yagi in the Eastern US.
But I think it's clear that 30 is worth the trouble and expense

But somehow my antenna at 20 ft has crushed pileups into Swains Island and some other places nearby. It may have been the arrival angle on that paticular day, hour and freqency (always 10 meters). Doesn't seem to work any more though LOL.

Take a look at the chart in section 2 here:
http://www.karinya.net/g3txq/hexbeam/height_2/

It shows relative performance vs height for short-haul, medium-haul, and long-haul paths on 10m and 20m.

But remember that sometimes it's worth sacrificing the odd dB of average Forward Gain if it means avoiding an elevation null in the spread of likely arrival angles.

73,
Steve G3TXQ
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