I'm not knocking the Diamond antenna, but be advised the gain claim is in dBi, not in dBd. Using dBi is a trick many antenna manufacturers use to inflate their gain claims.
dBi is decibels relative to an isotropic source, which is a theoretical source that radiates evenly in all directions. Because it radiates equally in all directions, the gain is 0. Such a source does not exist in the real world. That is why most honest companies give their gaim claims in dBd, or decibels relative to a dipole. A dipole does have gain relative to an isotropic source, so referencing your gain to it is much more useful outside of research papers.
If an antenna is claiming around 2.14dBi gain, then it is actually 0dBd gain. They are basically saying it has the same gain as a dipole, and the relative difference between a dipole and a dipole is 0. The relative difference between a dipole and an isotropic radiator is about 2.14dBi. That is how they arrive at their claim.
Saying an antenna has 2dB gain or 8dB gain is useless since since you don't what the gain is relative to. Decibels are a way to compare different values, so you have to know right off the bat what you are comparing. Other common examples are dBm which is decibels relative to one milliwatt, and db-MEG which is used when comparing to specific objects like a two specific antennas.
For what it's worth, I advertise all of my antenna gains in dBd.
Jeff
