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Discussion in 'CB Antennas' started by Capt'nCrunch, Mar 10, 2010.
Never put a gamma on the top of the horizontal element, this is to prevent heavy birds from roosting on it.
Vertical elements should be positioned, when possible, so water cannot settle and not drain out of the capacitor section.
Gammas can be mounted either to the top or bottom side of the vertical element, depending on considerations above.
Im guessing the gammamatch is still attached to the radiating element ? in that case..
Is there anywhere we could back-up those claims?, im a bit sceptic..i dont think it will make the forward pattern much tighter..and reduce back rejection..
If the forward patern becomes much tighter, that would probarbly implicates the gain would enhance too.
And if the front to back improved..that often means the gain will go down or you will sacrifice in bandwidth.
If it is true...why wouldnt all the antenna companies use it in that way. Everyone wants a tigther pattern and better FB ?
Ofcourse i understand that your thougths are that it is true..but is there any change i could get some facts ?
In any case, placing that match in front of, or behind the element isn't going to change the gain or 'sharpness' of the resulting radiation pattern, or it's F/B ratio.
A gamma match 'skews' the radiation pattern of a beam? Yes, VERY slightly. And so do a 'ton' of other things near that directional antenna, that's normal. The 'perfectly' formed, 'smooth', pattern representations you see are the results of statistical 'smoothing' done to make the resulting pattern uniform. All the antenna modeling programs do that. And YOU do that when graphic the results of taking measurements and plotting them on paper. You sort of 'average' out the plotted points, make it a 'smooth' curve.
And then when you come down to actually putting a directional antenna into use, does your rotor really point things that accurately? There's no 'play' in the whole structure that the wind doesn't 'play' with? Those "one degree" marks on that rotor indicator's dial are for filling spaces, not because the rotor is that accurate. (They do make handy reference marks though.)
[Reminds me a lot of the 'jiggle' correction thingy in the newer digital cameras, but you'd better have some extra memory for that thing to work.]
Why don't you find those matching devices on top of, or below the driven element? Mostly because it increases the 'sail' area of the antenna, which isn't the best idea in the world.
Think about it, then tell me how I'm wrong.
In most antenna designs, the feedline impedance will be 50 ohms, but usually the feed point impedance of the Yagi is rarely 50 ohms. In most cases it can vary from approximately 40 ohms to around 10 ohms, depending upon the number of elements, their spacing and the antenna's pattern bandwidth. If the feedline impedance does not equal the feed point impedance, the driven element cannot transfer the rf energy effectively from the transmitter, thus reflecting it back to the feedline resulting in a Standing Wave Ratio.
It seems to me the reasons for the Gamma Match is to match impedance and it doesn't matter if its to the left, right, or center. I like the bottom left side on driven element. A WELL FED YAGI IS A HAPPY YAGI!
I will tell the folks down here that have done extensive testing with the same antenna and the only changes they have made were changing the position of the gamma. They are the ones that did it and I have witnessed the effect first hand but like I said have never done it myself.
I like to have the gamma under the boom on the driven element myself. It has always seemed easier to get the desired tuning that way. This is what I have found, your experiences may differ.
BC, I question how that little bit could result in on-air detectable results too, but you saw what you saw. I'm curious, why don't you describe for us how the testing was done and what you observed?