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Antenna height for beam?

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  #25  
Old 04-16-2011, 10:29 AM
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Default Antenna Height for a Beam?


For CB first consider FCC Rules Part 95.

§ 95.408 (CB Rule 8) How high may I put my antenna?
(a) Antenna means the radiating system (for transmitting, receiving or both) and the structure holding it up (tower, pole or mast). It also means everything else attached to the radiating
system and the structure.
(b) If your antenna is mounted on a hand-held portable unit, none of the following limitations apply.
(c) If your antenna is installed at a fixed location, it (whether receiving, transmitting or both) must comply with either one of the following:
(1) The highest point must not be more than 6.10 meters (20 feet) higher than the highest point of the building or tree on which it is mounted; or
(2) The highest point must not be more than 18.3 meters (60 feet) above the ground.
(d) If your CB station is located near an airport, and if your antenna structure is more than 6.1 meters (20 feet) high, you may have to obey additional restrictions. The highest point of your
antenna must not exceed one meter above the airport elevation for every hundred meters of distance from the nearest point of the nearest airport runway. Differences in ground elevation
between your antenna and the airport runway may complicate this formula. If your CB station is near an airport, you may contact the nearest FCC field office for a worksheet to help
you figure the maximum allowable height of your antenna. Consult part 17 of the FCC’s Rules for more information.

WARNING: Installation and removal of CB station antennas near powerlines is dangerous. For your safety, follow the installation directions included with your antenna.

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  #26  
Old 04-16-2011, 05:09 PM
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There is no "best" height above ground for any antenna. There are some fairly good rules of thumb though, but they are only that, approximations.
On the average, something like a wave length above ground is nice. The only reason for that is that's where the dirt 'ground' stops playing a large part in the input impedance of the antenna, and where any directionality from non-multi-element antennas starts to really get 'directional'.
To some unknown degree, more higher tends to be more better. That "unknown degree" thingy is dependent on the antenna's environment, what's around it, etc. That's different for all installations so is unpredictable to a large extent.
'Best height' is whatever height you can manage. Less than one wave length? That'll work just fine (and has for a lot of people) too. You may be 'giving up' something, but unless you are lowering that antenna to only one wave length above ground, how would you ever know? Add in that "Momma Nature' has the final hand in what you hear because of 'her' propagation, and it's a chance either way. And because there's nothing "set in stone" about that one wave length height, a few feet either way just won't make a 'world' of difference either way. Agonizing over a couple of feet is silly!
- 'Doc
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Old 06-29-2012, 09:40 PM
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PDL2x4.JPG

Shockwave, your boy better hurry! The PDL4 has been in service for years! It's a PDL2 and a MR4 combined at around 14 DB. I have one in my utility trailer that I received from the builder last week. It'll be reaching out and touching you in a few weeks!

Okie, unless your stacking beams, you don't have to go crazy with concreting base sections, adding multiple guy lines or the such. The wind here in Oklahoma is a little trying but your probably not gonna go higher then 60 foot to the tip. The damn lightning and freezing rain is what I worry about here. If you end up with a beam put the boom at at least 36' and it'll work very well. As stated height is might though!

Okie can you still get a handle on the PDL? We have a machinist that's making the non-conductive hubs and I'd like to put together another one!

Thanks

Everyone have a good Independence Day!!

Driftwood

Last edited by IRock817; 06-29-2012 at 09:50 PM.

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  #28  
Old 06-29-2012, 10:24 PM
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It sure looks good.

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Old 07-01-2012, 04:13 AM
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Height plays a big part in what you hope to achieve, especially if we are talking about trying to work the other side of the World on a regular basis, or content with a maximum of a couple of thousand miles, the arrival angle for signals from different parts of the World should be in your consideration when planning an antenna installation. This is one of the main benefits when stacking antennas, one chap I speak to regularly in Australia has a 200' tower with four stacked five element mono band yagis, granted this isn't for CB, but the same rules apply, he is consistently stronger on his top antenna, by some 20 - 30db, than he is on his lower antenna at 60', that is all down to the lower arrival angle of his signal being near horizontal, I can talk to him long after propagation to his part of Australia has all but died out.
What causes this lower angle is the effect ground has on the take of angle, his lower antenna having a higher take off angle than his upper antenna. If all the OP wants to do is work a friend 60 miles away, then I'd want to make sure your friends antenna is in the same plane, ie horizontal or vertical, it would be a waste of effort mounting a yagi flat side if your friend only has a vertical antenna, with around 26dB of cross polarisation loss, you'd be worse off than you are now.

HTH

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  #30  
Old 07-05-2012, 09:06 AM
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This is a tricky question unless you're talking line of sight. Then the answer is easy. The higher the better. Not so much the case for DX work. As was mentioned, one wavelength is good but tends to favor short hop skip out to around 1500 miles on this band.

Going higher will lower the angle of radiation but it also breaks the main lobe up and places more nulls in the pattern. For example many Yagi's will produce a TOA of about 14 degrees at one wavelength. That is good for lots of DX. At two wavelengths you now have a deep null right at that 14 degree TOA but you have a nice peak just above and below the 14 degree null.

Where we had the strongest signal targeted at 14 degrees, we now find the weakest signal their due to that deep null. Years ago a friend donated a few extra sections of tower to me and I couldn't resist using them. My signal on the flat side went up to people in my state but most of the DX I had been working at a lower height was gone.

Conditions back then were not favoring long hop skip or coast to coast contacts so I essentially spent a weekend wasting a lot of time and effort to cripple my station. Now I understand how high I want to go is determined by where I want to talk.

One other advantage with the one wavelength height is that it produces the widest vertical beamwidth so it can target a broader range of angles without deep nulls in the pattern that can totally block out certain geographic locations. The tradeoff here is since the lobe is broader it's also not as strong as a narrower beamwidth would be.
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  #31  
Old 07-05-2012, 09:47 AM
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Quote:
Originally Posted by unit_399 View Post
OKIE -

The tower you have is perfect for 11 meters. The PDL is a better choice than the Moonraker because of the wind loading thing, and is better than the Maco because you have both vertical and horizontal polarization with the PDL.

- 399
Maco makes dual polarity beams" I would say call Maco and by a Gizmotchy 3 element dual polarity their great antennas and weigh only 113 pounds assemled you can always add another element kit later.
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  #32  
Old 07-05-2012, 10:01 AM
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Quote:
Originally Posted by TonyV225 View Post
Maco makes dual polarity beams" I would say call Maco and by a Gizmotchy 3 element dual polarity their great antennas and weigh only 113 pounds assemled you can always add another element kit later.
I think you added one too many ones.
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