I have an Imax 2000 mounted 50' to the feedpoint. I want to put up a m103 beam at around 30' on the flat. My question is will I see any gain in the flatside m103 at 30' compared to the imax at 50. Or is it a waste of time being so much lower.
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Is it worth it
- Thread starter canoe
- Start date
With both, you have covered both bases.
Feedpoint height will affect the skip angle. If both antennas have the same angle of radiation; then the different feedpoint heights might give different results. It is better to have it higher; but this will affect the skip takeoff angle. Nothing wrong with running it at 30 ft at all. Should work just fine. All that will do is change the skip takeoff angle. I run mine at 1 wavelength above ground (~36 ft); but you can run it higher or lower. Higher is better - IMO.
http://www.worldwidedx.com/amateur-...myth-surrounding-antenna-take-off-angles.html
Feedpoint height will affect the skip angle. If both antennas have the same angle of radiation; then the different feedpoint heights might give different results. It is better to have it higher; but this will affect the skip takeoff angle. Nothing wrong with running it at 30 ft at all. Should work just fine. All that will do is change the skip takeoff angle. I run mine at 1 wavelength above ground (~36 ft); but you can run it higher or lower. Higher is better - IMO.
http://www.worldwidedx.com/amateur-...myth-surrounding-antenna-take-off-angles.html
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I think it would be a safe bet that the beam antenna will hear more than the omnidirectional vertical in particular directions, right? That's the whole purpose of directional antennas. The difference in antenna heights will make some difference at times, but on the whole, that directional antenna will 'do' better.
I don't know what the gain of that m103 is, but it's more than a typical 5/8 wave vertical. The 'catch' to that is that the m103 will have to be pointed in the right direction for you to take advantage of that difference in gain.
'JI' pointed out that it isn't just a matter of the gain, or the take off angle, but the combination of all of an antenna's radiation characteristics. Keeping that in mind, 'Momma Nature' still controls/determines the 'best' height for an antenna to hear a particular signal. Signals almost never always arrive at your antenna at your antenna's 'sweet spot' all of the time. That arrival angle/take off angle changes all the time. To keep that 'sweet spot' -AT- the 'sweet spot' you have to be able to vary the antenna's height along with it's pointed direction. Can you imagine how much trouble that would be? And then 'Momma Nature' isn't very constant, 'she' changes things on a whim, it seems. If cost were no object being able to vary the antenna's height, or having several antennas at varying heights would be nice! (Don't know about you, but I am very doubtful that I could afford that.)
Gain and TOA can be 'worked around', just takes more ability from the operator doing that 'working around'. Things very seldom work out exactly 'right', so when they do, mark it on the wall!!
- 'Doc
I don't know what the gain of that m103 is, but it's more than a typical 5/8 wave vertical. The 'catch' to that is that the m103 will have to be pointed in the right direction for you to take advantage of that difference in gain.
'JI' pointed out that it isn't just a matter of the gain, or the take off angle, but the combination of all of an antenna's radiation characteristics. Keeping that in mind, 'Momma Nature' still controls/determines the 'best' height for an antenna to hear a particular signal. Signals almost never always arrive at your antenna at your antenna's 'sweet spot' all of the time. That arrival angle/take off angle changes all the time. To keep that 'sweet spot' -AT- the 'sweet spot' you have to be able to vary the antenna's height along with it's pointed direction. Can you imagine how much trouble that would be? And then 'Momma Nature' isn't very constant, 'she' changes things on a whim, it seems. If cost were no object being able to vary the antenna's height, or having several antennas at varying heights would be nice! (Don't know about you, but I am very doubtful that I could afford that.)
Gain and TOA can be 'worked around', just takes more ability from the operator doing that 'working around'. Things very seldom work out exactly 'right', so when they do, mark it on the wall!!
- 'Doc
Canoe, depending on how well your M103 is working, you will certainly see some differences in how these two compare, however you might also be surprised at how little difference you might see at times. And the difference in height of these two can certainally add complexity for such comparisons in response.
With DX signals you might even see the beam fully copying signals where the Imax might only hear some copyable audio, no copy audio, or nothing at all. Of course depending on the value of rejection for the beam at some angles, you might also hear better on the Imax at times, but in my opinion the differences much of the time are in the more moderate range...where both antennas can fully communicate.
IMO, the biggest differences might surprisingly occur when working local signals between vertical and horizontal radiators, and then it will be less likely that the beam will ever be able to reject all of a signal in some direction. I know guys that work beams 100% of the time with local traffic, and they hardly ever move their beams...they just learn to put up with the changes in signals they see as a result of not pointing in the direction for the best signal.
With DX signals you might even see the beam fully copying signals where the Imax might only hear some copyable audio, no copy audio, or nothing at all. Of course depending on the value of rejection for the beam at some angles, you might also hear better on the Imax at times, but in my opinion the differences much of the time are in the more moderate range...where both antennas can fully communicate.
IMO, the biggest differences might surprisingly occur when working local signals between vertical and horizontal radiators, and then it will be less likely that the beam will ever be able to reject all of a signal in some direction. I know guys that work beams 100% of the time with local traffic, and they hardly ever move their beams...they just learn to put up with the changes in signals they see as a result of not pointing in the direction for the best signal.
RatsoW8
Supporting Member, W9WDX ARC Member - WD8T
Along with what everyone else said your signal to noise ratio will be much improved. the yagi is horizontally polarized and giving you signal and noise rejection off the sides and rear. You will notice a difference.
Take off angles
I liked your original post better robb.
I do question the validity of the take off angle myth article when applied to the very narrow bandwidth of CB.
The article is persuasive and I'm all for avoiding nulls in the forward pattern but it's author uses frequencies that can and do arrive at much higher angles than CB frequencies do.
NVIS doesn't work at 27 MHz so there is a critical angle past which the signal is not reflected back to earth but escapes into space.
So there is a range of angles where the signal is most likely to arrive at and designing an antenna to concentrate its gain at those angles at the expense of angles that are (relatively) sure to have no useable signals is good designing.
Gain is only achieved by creating nulls where sensitivity is not needed or desired.
The article does bring up some important points like eliminating angle related nulls.
In the horizontal polarized world as you increase the height of an antenna gain increases with height until some (optimum) height where forward gain decreases and a new lobe forms at a very high angle. Further increasing height causes the main lobe and the new lobe to lower closer to the horizon but there is a null between the two lobes. If you go still higher you get more lobes and more nulls. Exactly what Tom warns about in the article.
You don't need to vary the height of your antenna for each signal just find a spot close to the optimum height.
The optimum I'm referring to has to do with the pattern not where the highest gain is but the gain you get is close.
I liked your original post better robb.
I do question the validity of the take off angle myth article when applied to the very narrow bandwidth of CB.
The article is persuasive and I'm all for avoiding nulls in the forward pattern but it's author uses frequencies that can and do arrive at much higher angles than CB frequencies do.
NVIS doesn't work at 27 MHz so there is a critical angle past which the signal is not reflected back to earth but escapes into space.
So there is a range of angles where the signal is most likely to arrive at and designing an antenna to concentrate its gain at those angles at the expense of angles that are (relatively) sure to have no useable signals is good designing.
Gain is only achieved by creating nulls where sensitivity is not needed or desired.
The article does bring up some important points like eliminating angle related nulls.
In the horizontal polarized world as you increase the height of an antenna gain increases with height until some (optimum) height where forward gain decreases and a new lobe forms at a very high angle. Further increasing height causes the main lobe and the new lobe to lower closer to the horizon but there is a null between the two lobes. If you go still higher you get more lobes and more nulls. Exactly what Tom warns about in the article.
You don't need to vary the height of your antenna for each signal just find a spot close to the optimum height.
The optimum I'm referring to has to do with the pattern not where the highest gain is but the gain you get is close.
