Antenna height

[jessejamesdallas]

Getting ready to buy a beam antenna to stick up on the tower, and have been looking at several, but my question is...

Which would be better to do.

"Have a 3 element beam on top of a 40' tower, OR a 4 element on a 30' tower"

I have a 30' tower now, and was thinking of maybe buying another 10' section to get it up 40', but with the tower I have which is a Universal self supporting tower, if I go up to 40, then my wind load at the top drops.

Way it is now, I have 9 sq. ft. wind load at 30', but if I go up to 40 ft., then it drops to 4.5 sq. ft. wind load, so I would have to use a smaller antenna at 40' then what I can have at 30'...

Just wondering if 10 more feet of tower would be worth it, or stay at 30' and get a little bigger antenna?

 

[Robb]

Having/using a beam is better than no beam, regardless if it is at 30 or 40 ft up.

A three-element beam will be more broad-banded, while the four-element beam won't, but it will have slight more usable gain.

That's pert near all of it - IMO . . .

 

[Captain Kilowatt]

The difference in gain from 3 elements to 4 elements is very minor and in fact you won't see it on air. The difference between 30 and 40 feet high is usually not quite so minor and in some cases over some paths can become quite noticeable. If those are your only hard and fast options then I would gor for 3 elements on a 40 foot tower.

 

[jessejamesdallas]

Not ever having a beam, that's basically what I needed to know, is if there was that much difference between a 3 element and a 4...

Right now at 30', my antenna only clears the roof line by about 6 or 7' since the house is a two story and the roof peaks at about 25', so another 10' section would get me up over the roof a little higher...

Now just have to decide on which antenna to go with...Been looking at the Maco's and Gizmo's, sorta leaning more towards the Gizmotchys since they look to be lighter...Just needs to be dual polarity which ever way I go so I can talk local as well as DX.

 

[Lil'Yeshua]

.

 

[Mudfoot]

Maybe take a look at some quad choices.

 

[jessejamesdallas]

Maybe take a look at some quad choices.

open for suggestions...

 

[Mudfoot]

http://www.cubex.com/CB.htm

 

[Henry HPSD]

For DXing from an electrical point of view, there won’t be difference between a good yagi and a good quad.
For local it’s a different story.(vertical) The Quad is advised as the quad is less influenced by mast/coax etc. You can imagine an antenna manufacturer carefully designing a yagi a fraction of a inch is important. And there we are ….pufff…a big mast in between the elements. That has and always will effect the antenna. You will only find vertical yagi’s which depend on matching systems in order to get a reasonable SWR and still…many struggle to get a decent reading. If SWR “changes” you can count on it your “pattern has been influenced as well.

The difference between a 3el and a 4el is not noticeable, unless.....
The one of the antennas is not performing to its ability. Or you are taking 2 "extremes". Say a 3el on a 2 meter boom will provide about 7dBI And a 4el on a 6,5 meter boom will provide about 10 dBi
With that said....the 3el has a probably much better overall pattern. And making a new "dx" contact is not always done with gain, but by illuminating the unwanted.

In reference to height:
Height is one of the most important things
Not now...as the sunspots are really high....you can work the entire world from a mobile whip. (I’m not around 150DXCC from my mobile /100 watts) But those spots will drop again, and the angle of which the signal arrives will become more important. And that angle for horizontal antennas is primarily influenced by height:

Height versus take off angle
http://www.hpsd.nl/wp-content/uploads/2013/03/take-off-angle.pdf

Both links might help to get a bit of understanding what height does.

So…advise …
A gizmotchy might be something I would not do. A search on this forum will provide insight in how bad some of the designs are…probarbly not all….but I would first verify the design at least.

Get a GOOD 3el Yagi put it up as high as possible. (preferably beyond 40 feet) and add a omnidirectional vertical.
Or search for the dual polarity cubical quad.


Kind regards

Henry 19sd348

 

[M0GVZ]

However whilst height can be good, too much height can be a bad thing depending the take off angle required for where you want to reach.

As you can see from this graph by G3TXQ, at 2 wavelengths high an antenna is actually worse than one half a wavelength high above 21 degrees take off angle being neaerly 20dB down over the half wavelength high at 13 degrees!!!!

What that means in reality is it'll work stations 6000 miles away very well but anything a few thousand miles or less you're really going to struggle in comparison to half wavelength up. Amateur radio contest stations will typically have two or three beams at different heights for each band so they can switch between them depending on where they're contacting.

 

[Lil'Yeshua]

Quad Antenna Calculator
http://www.qsl.net/yt1vp/CUBICAL QUAD ANTENNA CALCULATOR.htm
http://youtu.be/BrVgcxVqwng
http://wb9dlc.com/lightningbolt.htm

 

[W5LZ]

There are some things that if you can get them 'right' at any particular instant, can make a huge difference in what you can hear (and conversely, who you can talk to). The trick is to get them 'right', right? And that 'right' depends on propagation, always. All things considered, the higher the better, the lower the TOA the better, etc. That will get you into the 'ball-park' 50% of the time. The other 50% it'll be 'not right', something could be adjusted to make it better. Fixating on any one aspect to the exclusion of others isn't exactly the 'best' idea in the world. So, Doing the best you can at any particular instant is all you can do. More is better to an almost ridiculous degree.
I don't know about anyone else, but I'd love to have all my antennas up a few thousand feet/meters. Not going to happen though, oh well.
- 'Doc

 

[The DB]

take off angle

I love it when people bring up take off angle... By itself it tells you pretty much nothing about the antenna in question. For a vertical antenna the vertical beamwidth of the radiation pattern and where the nulls in said pattern are will tell you so much more. Further, the angle of maximum RF radiation is rarely centered within the vertical beamwidth of the antenna. The two angles that make up the vertical beamwidth will be far more accurate than a take off angle at showing where your antenna will actually radiate. And that is just the start of why the take off angle number, by itself, is useless...


The DB

 

[M0GVZ]

I love it when people bring up take off angle... By itself it tells you pretty much nothing about the antenna in question.

Getting ready to buy a beam antenna to stick up on the tower

We've been talking about yagis, the image clearly mentions dipoles as well as a quarterwave vertical for comparison. I think you can safely assume we're talking about horizontal antennas.

And yes, for TOA a horizontal yagi behaves the same as a horizontal dipole.

 

[The DB]

We've been talking about yagis, the image clearly mentions dipoles as well as a quarterwave vertical for comparison. I think you can safely assume we're talking about horizontal antennas.

And yes, for TOA a horizontal yagi behaves the same as a horizontal dipole.

So what your saying is what I said in relationship to take off angles is correct for both types of antennas... Thanks, that makes it easier on me...


The DB