Antenna Gain Question

[goaheadover]

I am looking at two antennas. one has a 2.5 gain and the other has a 6.1 dbi. does the higher gain mean i will be able to receive things better? the higher gain the better? thanks

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[n3ezt]

Not to get to overly technical, but in a nutshell, yes, the higher gain antenna should receive more, but it can also add over load to a sensitive scanner and you'll actually receive LESS due to desensing the receiver. Stick with a 3-5db gain antenna and you should be ok. Use a local wx channel for comparison while switching antennas off and on.

 

[prcguy]

If both antennas use the same reference, then the larger number would receive and transmit better. Problem is there is dB gain compared to a dipole (dBd), gain compared to an isotropic source which is a theoretical modeled thing that has 2.14dB less gain than a dipole. Then there are pure fantasy gain numbers made up by some antenna companies simply to sell antennas. In other words, their gain numbers are lies.

The challenge is navigating the advertisements looking for dBd or dBi listed in ads or having some antenna knowledge where you can look at an antennas construction and know roughly how its made and how much gain it might have. Hopefully I have not added further confusion to your question.

I am looking at two antennas. one has a 2.5 gain and the other has a 6.1 dbi. does the higher gain mean i will be able to receive things better? the higher gain the better? thanks

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[Ubbe]

Give us the link to the two antennas and what frequencies you want to receive.

/Ubbe

 

[W5lz]

Another aspect of this is that the gain differejnce between those two antennas is negligible, simply not enough difference for you to ever hear. Dbd and dbi. First, deduct something like 2 db from that dbi figure and you have the -actual- difference. Also keep in mind that db measurements are a 'relative' thingy. A fraction of a db just doesn't make any difference until you get to really large numbers.

 

[ko6jw_2]

Another aspect of gain is that no antenna has "gain." All they really have is a radiation pattern that is more horizontal. Thus, the signal is concentrated closer to the ground and is, theoretically, better. But, what if you are listening to aircraft or are using the antenna on a mountain top repeater? That nice horizontal pattern won't hear an aircraft at 40,000 feet above and your repeater will be sending power to the horizon, but not to the operators 5,000 feet below.

A friend of mine owned a local radio store back in the day when such businesses existed. He had a yagi on display that said it had 127Db gain. In small print it said "127Db gain over an isotropic noodle sealed in a lead box and buried in a cesspool." Some claims (Amazon in particular) are not much less exaggerated.

 

[W5lz]

That about the aircraft and/or mountain top isn't exactly true in all cases, and really does depend on frequency to a great extent, power too, but that really opens that can of worms. As in 'density'/foot and receiver sensitivity. (It's early, I haven't had even one cup of coffee yet and I ain't gonna even try to remember how to explain that! ...sorry)

 

[WB9YBM]

I am looking at two antennas. one has a 2.5 gain and the other has a 6.1 dbi. does the higher gain mean i will be able to receive things better? the higher gain the better? thanks

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"DBi" means DB gain over an isotropic antenna (that's what the "i" means). Typically antennas are referenced to a dipole (DBd) in the case of horizontal polarization, or quarter wavelength antenna for vertical polarization (usually expressed simply as "DB"). Typically "DBi" is one DB above the more standard DBd or DB spec's (it's the sales department playing games to make their antenna look better than the competition).