Can someone explain to me what is omni gain and offset gain? The antenna has 6dbd omni gain and 9dbd offset gain. I could use a layman interpretation out there if anyone can explain it to me.
Antenna gain
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mmckenna
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Which antenna are we talking about?
Laird YDA 4504
mmckenna
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Thanks, that helps.
The multi-bay folded dipoles have the benefit of being able to reorient the elements to get the coverage you want.
"Omni gain" is when you have the elements evenly spaced around the mast. In the case of this antenna, it's an element every 90 degrees, in others words, one pointing North, one pointing West, one pointing South, and one pointing East.
That'll give you the 6dBd of gain.
If you put all 4 on one side of the mast, they become more of a cardioid pattern (heart shaped). That'll give you the 9dBd of gain as all the elements are pointing in one direction.
What would happen if you put 2 hypothetically pointed nort and 2 pointed west for instance the first north, second west, third north fourth west?
mmckenna
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You'd get a pattern that covered better to the North and West somewhere between 6 and 9dBd gain, and less coverage to the South and East.
mmckenna
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It's up to you. The only requirement is keeping the elements spaced properly vertically.
On some higher end antennas, you can also change the distance between the mast and the element to change the pattern. Not sure if that model will allow you to do that.
On some higher end antennas, you can also change the distance between the mast and the element to change the pattern. Not sure if that model will allow you to do that.
Ubbe
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You can't adjust it but you can order it with a 1/4 wave or a 1/2 wave distance to the mast, depending of what you want to achieve with the pattern.
/Ubbe
/Ubbe
I don't mean to hijack thread, I only ask for educational purposes.
I'm assuming from what I'm reading, on these type of antennas, you can actually adjust this omni directional antenna to be more direct to the area you want to listen to, however this is not considered beaming?
An element offset from the mast about 1/4 wavelength will be similar to a 2 element beam. Same element 1/2 wavelength out from the mast gives a figure 8 bi-directional pattern. Multiple dipole arrays can be oriented for omni or cardioid or bi-directional, etc.
mmckenna
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Spacing the elements out from the mast makes them act like a 2 element beam antenna.
If you look at this sheet from Telewave for their ANT450 UHF dipole antennas, you'll see the pattern shown near the bottom based on spacing from the mast:
Ok, I see the pattern each illustration gives, what would that equate to in inches? How do you calculate it?
mmckenna
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Thanks a lot. That makes it real easy.
What happens if you have two elements and you install both , back to back pointing in total opposite directions , at the very top of the mast?
Will it act like a beam forward and backward?
mmckenna
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Depends on the spacing, but will sort of give you a bowtie pattern. You may see antennas set up like this for railroad/transportation applications where the necessary coverage tends to be linear.
Each dipole will have several dB gain away from the mast but you will loose 3dB splitting the coax to two antennas. Net gain will be low with a figure 8 pattern.
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