Yet another dumb ????? (about TOA's)

[wyojeepeer]

Quick question that I don't know the answer to.

If you change the down angle of the ground plane radials IE: 90*, 45*, 20*, does that change the takeoff angle, significantly?????
I've seen it discussed about impedence IE: 90*=36 ohms, 45*= 50 ohms, and ~20*= 75ohms, but, not weather that affected the TOA.

Thanks, John.

 

[Crawdad]

Take-off angle is a function of height above earth not ground plane angle. Plenty of antenna info out there at the end of your Google fingers...........

 

[wyojeepeer]

Take-off angle is a function of height above earth not ground plane angle. Plenty of antenna info out there at the end of your Google fingers...........

See, I learned something today.

It still don't seem right to me..... but, I'm old, now.
It's been over 50 years since I needed Ohm's Law (or, what the color codes on resisters mean). ARRL manuals are your friend.

Thanks, John.

 

[The DB]

Crawdad is right, height really is might in this regard, the higher the antenna the lower the angle of radiation.

To a lesser extent, the quality of of the earth below also plays a part.

Seriously though, I wouldn't worry about the "take off angle" at all. Put up the antenna and see if you make contacts. Also, read the thread "The Myth Surrounding Take Off Angles" (that is a link by the way), which was posted and stickied in the Ham Radio Antennas section of this forum.

All to often people get to hung up on side details like "take off angles".


The DB

 

[Henry HPSD]

Hello,

Possibly there are situations where it isnt always true that the higher we place the vertical antenna...the lower your take-off angle will be.

Specifically not, if you have relative good ground around you.
That ground actually playes a significant part.
(it is open to debate what would be significant though hihi).

4NEC2 qualifies "Pastroral, low hills, rich soil typical from Dallas, RX to lincoln, NE as "very good" ground. (in blue below)

(I also added the pattern of very poor ground (green) and the so called average ground (black)for reference).

If we take a random dipole antenna :
(from : How high should I place my vertical CB-Antennas.com )



We can see the take-off angle for the very good ground situation is actually higher compared to those with worse ground capabilities.

For very good ground It might be wiser in those situations to leave the antenna near the ground. (for DXing). If we take a tradiational 1/4 wave groundplane with 4 radials and place it 0,5 meters above that very good ground and we place it 5,5 meters above it we will roughly have :



Where the majority of the signals arrive at a 10-20 degree angle the low placed vertical groundplane actually has an advantage over the higher placed one.
(for very good ground).

If it were me, i always worry about take-off angle.
As im into 'DXing", but ill admit ..perhaps im a bit over excited.

It is without a doubt during the solar peaks, you are able to work anything with a mobile antenna. The advantage of take-off angle becomes clear when propagation is not in your favor and you only have a small window of opening.
Then it really is the case of beeing able to work that special DX ....or not.

Perhaps that is the "key" to any conclusion or contribution....
If you find several dB's to be significant or not....but that is up to you.

Kind regards,

Henry

​

 

[Crawdad]

Seriously though, I wouldn't worry about the "take off angle" at all.

I used to worry about it until I started using antennas that were lower than I'd like them to be. 10k mile contacts with a 20m two-element beam less than a half-wavelength above earth helped me to stop worrying..........

 

[wyojeepeer]

So....
I did "Google" it.

I did read the TOA myths, for the third or fourth time.
Based on the description of TOA in that article, I can't see where you can have very much of a change in 20 or 40 feet of height. Maybe in miles, but not feet. I imagine a teeter-totter with the fulcrum at 20 to 80 miles. I think that what you're seeing is getting the antenna closer to iso(something or other), away from the the Earth Ground.
If a 1/4 wave is noted for having high lobs, and a 1/2 wave as having lower lobs, and a 5/8 wave as having lower yet, I'm assuming that they each have a different TOA. Now, because dropping the angle of the Ground Plane Radials results in "DB Gain", it should follow that it has changed the lobs to a lower value/angle. That should change the TOA? By how much, I have no idea. Hence the question.

Thanks, John.

 

[Henry HPSD]

Hello John,

To answer your question:
The difference between 90 and 45 degree angle of the radials with a quater wave groundplane is neglible.

Here is the expected antenna pattern for a groundplane say 33 feet above ground (average ground conditions)
Black is with a 45 degree angle and blue in 90 degrees.


Im not sure im reading you correct...If you are saying: you think that a vertical 1/4 wave length antenna has a higher radiation angle then a halve wave vertical and a 5/8 wave vertical actually has the lowest that is incorrect. (although that is often mentioned as a sales gimmick, and mentioned on less accurate websites.).

Below you can see in green a 5/8 wave vertical with 4 radials 33 feet up and a 1/4 groundplane (in blue) with 4 radials 33 feet up and the dipole in black).

There isnt a much lower take off angle amongst any of them.



As is mentioned...that take-off angle depends on heigth above ground and the how good the ground is from an electrical point of view.

But overall, verticals dont need to be high in order to have a low take-off angle.
They can be sitting on the ground and you can work the entire world with it.
That is a different story for horizontal antennas.

Kind regards, Henry.

 

[wyojeepeer]

Thanks, Henry.
That helps a lot.
I got another question. On your plots above, am I correct in assuming that would be a side view of a vertical antenna?
I never saw this kind of stuff 40 years ago, and am still learning.

Thanks, John.

 

[wyojeepeer]

ya know, sometimes I feel like I'm chasing butterflies, with a cannon.

John.

 

[Henry HPSD]

Hello John,

Yes...that is correct.
That is called the elevation pattern and is viewed from the side.
The pattern you see when looked from above is called the "azimuth" pattern.
You can read a bit more about those plots here:

Radiations Patterns – 19DX348 CB Antennas

cb-antennas.com

Kind regards,

Henry