Thread: UHF antenna rating dBi

Recalling my 30 year ago radio theory but here goes.

I'm pretty sure "dBi" refers to dB gain over an isotropic antenna, which is a theoretical antenna with zero gain. You can't make an isotropic antenna.

The other way to reference gain is to a standard half wave dipole antenna which has about 2.2dB gain over an isotropic (again only theoretical ). This "dBd" measurement is more practical because a dipole antenna can actually be built and other antennas tested against it as a reference. A quarter wave ground plane antenna looks electrically like a half wave dipole.

If you Google isotropic antenna you will get more on the theory.

your 30 year recollection has stood the test of time.

db is a ratio (power ratio) dbi is a ratio with respect to an isotropic antenna.

an isotropic antenna is theoretical and it sends power out in all directions evenly spread. A bit like the energy that is radiated away from the sun, just as much out the sides as out the top, you get the picture

So why would they change the rating for consumer antennas across the board?
I think it is weird not even GME mention the change on their website.

Read what is said above!

If dBi is 2.2dB "more" than using dB over a dipole they get a bigger number.
Bigger the number means it must be better, yes? Actually no it doesn't of course, they are just using a different reference point.


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Originally Posted by miky

Read what is said above!

If dBi is 2.2dB "more" than using dB over a dipole they get a bigger number.
Bigger the number means it must be better, yes? Actually no it doesn't of course, they are just using a different reference point.

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quite correct...to get a bigger number 'cause size counts