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Antenna Height

C

caspear1978

Member
Jan 8, 2009
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Howdy folks, been thinking about going up higher with my Pdl 2. Right now to the very top of the antenna, I'm at 36 feet from the ground.

Was thinking about going another 15 feet higher. will going higher be better as far as skip goes or will it be pretty much just better for local talking? What are the advantages of going higher with an antenna?

I know ive read some where before about the TOA of the signal , but don't remember which was better for talking DX. Will it also effect the Receive side as far as picking up more stations or would it be the same.

Guess im just wondering what the overall Performance will be if I went highe

778 Northern Minnesota, clear and on the side
 

For a 10M/11M antenna, 36 feet is the minimum height for optimum ground wave (local) coverage. An extra 15 feet will improve ground wave (local talking) a bit. That extra 15 feet will do nothing for your DX coverage, as you're already at the minimum height for good DX. That extra 15 feet is a very small difference to the ionosphere which reflects your DX signal. At about +/- 1000 miles up, the ionoshphere won't notice the difference.
 
Ok so it'll give me better results for local talking. but for dx it'll be the same no matter what height its at for my setup. Im running 11m so was just wondering if it would make a difference or not. Thanks Ed for the heads up on this...
 
id say any difference is gonna be greatly effected by the geography of your location and structures nearby .
 
Actually, there wouldn't be a lot of difference, local or DX, with an additional 15 feet of height. I'm sure there may be some difference but doubt if it would be very noticeable.
Just for grins, antenna height is usually measured in reference to the feed point, or bottom of the antenna, not the tip. The antenna's length isn't counted as height.
- 'Doc
 
I also have a question about antenna height. Since I think Caspear's question has been answered, I'm going to ask mine. I'm not trying to hijack this thread.

I have a home-made 2-element quad that I built a few months ago, but I still haven't gotten it up. (It takes me longer to get anything up now-a-days.) I would like to "fine tune" the antenna before putting it up permanently, and need to know the MINIMUM height I could use and get reliable readings SWR-wise. FREECELL said I could just lay the antenna with the director flat on the ground and set it up that way. Any opinions ? Thanks.

- 399
 
The bottom line is that "higher is always better". That 15 feet might just put you above some local structural or geographic obstruction. That PDL II is an interesting dual-polarity antenna. You should have a lot of fun with it.
 
- 399,
For once, freecell is right. That setting a beam on it's reflector to tune it on the ground does work. There will be some differences once it's in the air, but it should at least be 'close'.
- 'Doc
 
caspear1978 said:
Howdy folks, been thinking about going up higher with my Pdl 2. Right now to the very top of the antenna, I'm at 36 feet from the ground.

Was thinking about going another 15 feet higher. will going higher be better as far as skip goes or will it be pretty much just better for local talking? What are the advantages of going higher with an antenna?

I know ive read some where before about the TOA of the signal , but don't remember which was better for talking DX. Will it also effect the Receive side as far as picking up more stations or would it be the same.

Guess im just wondering what the overall Performance will be if I went highe

778 Northern Minnesota, clear and on the side
Click to expand...

Not predictable, for reasons given by several earlier. If you have a question about changing an existing antenna configuration, there's only one way to know for sure, and that's to try it for yourself, in your location, with your equipment, and see what results YOU get.

May not be the same for others; my results might not be the same as yours.
 
caspear1978 said:
Howdy folks, been thinking about going up higher with my Pdl 2. Right now to the very top of the antenna, I'm at 36 feet from the ground.

Was thinking about going another 15 feet higher. will going higher be better as far as skip goes or will it be pretty much just better for local talking? What are the advantages of going higher with an antenna?

I know ive read some where before about the TOA of the signal , but don't remember which was better for talking DX. Will it also effect the Receive side as far as picking up more stations or would it be the same.

Guess im just wondering what the overall Performance will be if I went highe

778 Northern Minnesota, clear and on the side
Click to expand...

Casper, I'm not too sure that the added height will be of much advantage, but more height, within reason for safety, is always better.

There is a technical viewpoint that quad type antennas are a bit more effective than yagis at lower heights, and if true then this is what I base my considerations on. It is always best to get the antenna above the surroundings that matter, like houses, and the typical buildings in the area. You might not get over the tree canopy, but that would be nice and is usually in the 2nd wavelength.

Personally, I would not consider raising a quad just 15' feet higher even if convenient and do-able unless it is a simple matter of just pushing the mast up higher. Maybe if it was convenient for me, I might go to 72'+ and try and get into the 2nd wavelength.

Just as a note. Someone mentioned improved ground wave communications on raising. I think if you check the definition for ground waves you will find this medium is effective for low and medium band communications below 3.0 mhz, but is basically none existent at HF and for sure in the high end of HF. Maybe the reference was meant to suggest line of site type waves could be improved with added height.
 
Last edited:
VA3ES said:
For a 10M/11M antenna, 36 feet is the minimum height for optimum ground wave (local) coverage. An extra 15 feet will improve ground wave (local talking) a bit. That extra 15 feet will do nothing for your DX coverage, as you're already at the minimum height for good DX. That extra 15 feet is a very small difference to the ionosphere which reflects your DX signal. At about +/- 1000 miles up, the ionoshphere won't notice the difference.
Click to expand...

Here are some examples of changing the height of a three element ten meter NBS Yagi-Uda (Mr. Uda was Mr. Yagi's partner in designing the Yagi antenna. Both gentlemen were Japanese.) at 28.025 MHz modeled with EZNEC+ 5.0 Pro:

Let's talk about gain.

Gain can be measured in two ways dBi and dBd. Most antenna manufacturers publish their gain figures as dBi because it sounds better, but it really means gain compared to a isotropic dipole in free space. Unless you can put your Yagi-Uda in space dBi doesn't mean much, so I'm going to use the calculator at Pure ERP And EIRP Calculator to calculate the true ERP, not the EIRP, using 100 watts of power.

I. At .5 wavelength (17.5481 feet) gain should be 13.15 dBi = 1259.378 watts ERP. with a radiation angle of 24 degrees.

II. At 1 wavelength (35.0962 feet) gain should be 14.62 dBi = 1766.673 watts ERP and a radiation angle of 15 degrees.

III. At 1.5 wavelength (52.6443 feet) gain should be 15.12 dBi = 1982.240 watts ERP and a radiation angle of 9 degrees.

IV. At 2 wavelengths (70.1924 feet) gain should be 15.09 dBi = 1968.594 watts ERP and a radiation angle of 6 degrees.

Hey! Wait a minute! We lost some gain! More later...

Notice that as we raise the height of the antenna the angle of radiation goes down, but in our last calculation we lost some gain.

Let's talk about angle of radiation:

The ionosphere is a reflective surface (not always ;o) ) and it is a sphere, so when we hit it from an angle of 24 degrees the signal bounces off at a different angle (probably the best angle for local communication) than at 6 degrees. Now you guys who shoot pool know that when you want to bounce the cue ball further down the table, you shoot at a shallow angle, not a high angle. Well the radio waves from your antenna are sort of like a cue ball. The higher the radiation angle of the signal the shorter the hop around the earth will be, so our dream antenna should have a radiation angle that is as low as practical (zero ain't practical), so by lowering the angle of radiation our signals bounce further around the earth.

In example IV we lost .03 dBi of gain, or 13.646 watts ERP. Do you think our loss of ERP can be detected on the other end? The answer is no.

My investigation seems to show that raising the height of a Yagi-Uda antenna improves it's performance up to 2 wavelengths in height.

73 from North Central Texas

Tom, N5GE
 

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