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The Myth Surrounding Antenna Take Off Angles
- Thread starter Captain Kilowatt
- Start date
Mount it less than 1/2 wavelength above true ground.
B
BOOTY MONSTER
Guest
B
BOOTY MONSTER
Guest
if you raise it higher to take advantage of the a lower TOA (per this thread) it's no longer a omni .... seems like a catch 22 ?
There are quite a few dipoles mounted at less than a 1/2 wave length above ground, even on 10 and 11 meters. They are probably just as 'omnidirectional' as some verticals the way those verticals are mounted (stuff near them). And then, what's the great benefit in being omnidirectional?
Most dipoles are not all that directional even when above a 1/2 wave length, more of a flood light than a spotlight, and will never be a laser by any means. Does that mean you won't hear everything all around you? You probably won't. But then, the same can be said for an omnidirectional vertical antenna. Dipoles tend to 'favor' certain directions, but then, so do verticals.
- 'Doc
Most dipoles are not all that directional even when above a 1/2 wave length, more of a flood light than a spotlight, and will never be a laser by any means. Does that mean you won't hear everything all around you? You probably won't. But then, the same can be said for an omnidirectional vertical antenna. Dipoles tend to 'favor' certain directions, but then, so do verticals.
- 'Doc
Correct Doc. People tend to think a dipole is fairly directional when in reality the two main lobes are really, and I mean REALLY, broad. It is the nulls that tend to be quite deep and fairly narrow.
There we go again being more concerned about the orientation of the nulls and not the forward lobes. The whole idea is not worrying about the imperceptible one or two dB increase you will get from optimal orientation of the antenna but be more concerned about the drastic 20 or 30 dB of loss due to improper orientation.This is Something that was revealing to me in regards to discussions about vertical antennas.
I realized that I needed to pay attention about if the vertical antenna being discussed was a ground based one with buried radials or a ground plane one elevated several feet above the earth.
There are significant differences in the performance and characteristics between the two type of verticals.
I know it is one of those Duuhh! moments, but it cleared up what appeared to be some contradictory observations in various text regarding vertical antennas for me.
I realized that I needed to pay attention about if the vertical antenna being discussed was a ground based one with buried radials or a ground plane one elevated several feet above the earth.
There are significant differences in the performance and characteristics between the two type of verticals.
I know it is one of those Duuhh! moments, but it cleared up what appeared to be some contradictory observations in various text regarding vertical antennas for me.
You are talking something different with regards to verticals. A ground mounted vertical with buried radials needs MANY more radials than one with radials on the ground. A vertical with radials on the ground needs MANY more radials than one with an elevated radial system. The reason is simply ground losses. In the first case the RF must travel through lossy ground before encountering the radials. In the second case the radials are in contact with lossy ground that forms a separate lossy return path. With elevated radials they are far enough from ground so as to not be coupled to it thus reducing ground losses.
Around 14 degrees seems very useful. That also happens when the Yagi is about 1 wavelength above ground. Verticals with elevated radials behave much the same way. While the nulls in a pattern can ruin the ability to communicate quickly, we have to remember that changing height effects lobes and nulls simultaneously.
If you noticed the 14 degree primary lobe was giving you good DX results in the desired target area, raising the antenna to two wavelengths would be disastrous for that same 14 degree target area. You just lined your deepest null up in the same place your strongest lobe was! Just some things to consider.
If you noticed the 14 degree primary lobe was giving you good DX results in the desired target area, raising the antenna to two wavelengths would be disastrous for that same 14 degree target area. You just lined your deepest null up in the same place your strongest lobe was! Just some things to consider.
Again more confirmation of the idea about not worrying about the lobes and worry about the nulls instead.
The original take off angles are correct for free space..Once these antennas are put over ground this changes drastically and varies from site to site..much like the belief a 1/4 wave ground plan is equal to a vertical dipole ..which in free space it is .place these antennas over real ground and once again the dipole wins. For the higher he bands a simple vertical dipole is an excellent do antenna..it may have no gain or 0dbd "it is a dipole" when mounted close to ground the take off angle is 0 ..While this antenna isn't directional it makes an excellent simple do antenna ..As with any vertical it's exact height above ground is determined by it surrounding ground and objects with in it ..also a low mounted horizontal dipole can easily have a reflector pulled up to make a non rotating 2 element beam . 2 dipoles "one facing north and south with the other facing east and west could easily be made to a poor man's beam antenna by attaching reflectors that can be raised and lowered quickly as needed or on 12 meters and up four separate beams can be built out of wire in a single tree with a switch to change directions with good results .take a lot of these manufacturer db ratings with a grain of salt.
Happy dxing
73
Happy dxing
73
With all the 11 meter antenna's I have ever used, the ones that worked the best - with the crappy AM / SSB CB radios was the antenna's that was placed in a free space ( nothing in the first and second Fresnel Zone ) somewhere between 30 and 60' in height.
For talking Locally - the higher antenna ruled, but for working DX, the most important thing that i found was that it was better to have a lower amount of noise and a weak signal then to have more noise and the same signal strength.
I'm sure that a lot of us started out with what we could afford and not what we wanted. The old Super Penetrators and 117 Super Magnum verticals were a good antenna for getting started.. Moving up to a 4 element horizontal beam and then to the MoonRaker IV, each move was an improvement over the previous antenna.
For working DX - when 11 is open it does not take a lot of power or a big signal to be heard. The key is to put as much aluminum up in the air as possible.
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I agree 100% with your gain assumptions and I often times get into shouting matches with the local hambones on two meters when they try to tell me that they have a 5/8 wave - two meter - trunk lip mounted antenna and it has 6 or 8 db of gain over a quarter wave antenna.
When I try to tell them that my 40" stick on the roof of my truck would out talk their 5/8ths wave and that even a 1/4 wave antenna on the roof of the truck - 7' off the ground, compared to their 5/8ths wave 3 feet off the ground is no comparison - they tend to get angry and shout just like the cb'rs they were before they became porkers.
The one difference is if you look at K3LR's station - you will see that he not only has beam antenna's stacked, he has them phased and can choose between which antenna's at which height he wants to use and choose the phase they are in when he uses them.
It isn't just as easy as sticking something up as high as you can get it and hope that it works when you are building a multi multi op's contesting station.
K3LR Multi / Multi Homepage
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