antennaes

[JJDinsay]

A little dumb on antennas but I do understand that they are probably the most important aspect of an AP. I have a DLINK 2000AP and a 3COM3CG Office Connect model. The DLINK has one antenna and the 3COM has 2 antennaes. Does this mean that the 3COM generates more coverage area because it has two antennas and therefore 2 seperate radiation patters for the signal? Dumb question I know but I don't know the answer. Is an omni the best antenna to use to provide coverage to rooms along a short hallway - maybe 50 feet end to end across 2 floors?

thanks,

[M/Q]

The two antenna system is called a antenna diversity. What it does is the firmware is smart enough to switch between the two antennas and determines which one is receiving the best signal. It then uses that same antenna for the next transmission. It checks this many times per second. So it allows the best signal to be used at all times. The single antenna does not have that feature. Also remember that it can only receive and transmit on one antenna at a time, not both.

As for best antenna that is a hard question, the omni-directional has a coverage area in the shape of a ring around the antenna. If it is in the center of the coverage area, it will work well. But if it is placed toward one end, then the signal going out the end where coverage is not desired is just wasted. In that case a panel or directional antenna would work better.

[JJDinsay]

So this radiation pattern for an omni really only covers clients on the same floor and the signal will not be good enough to reach floors above and below the AP? I'm pretty much looking for a recommendation for an antenna where it generates a radiation pattern that resembles a sphere with the antenna at the center. This signal would radiate to any AP's located in floors both above and below it.

thanks for the feedback

[james]

An omni-directional antenna would generate a somewhat spherical pattern. Keep in mind that there is a lot of variance depending on which way you orient the antenna, i.e. horizontal or vertical. The higher the gain on the antenna, the flatter the signal pattern will be. If you check out http://www.hyperlinktech.com/ you can see a few pictures of the difference between omnidirectional antennas of different gains, check on the product pages of the different antennas. Also, the composition of the floors will play a big factor, but one floor in either direction shouldn't degrade the signal too horribly, as long as you remain within close proximity to the AP. What exactly are you trying to do?

[M/Q]

Sorry, but being a RF geek and an amateur radio operator I will have to advise that there is no such antenna that will give a truly spherical coverage area. That is called an isotropic radiator. All antennas in any application are compared to it and then are given their gain factors. Even a normal little vertical dipole on the consumer device has approximately 2dBi gain, which means 2 dB over an isotropic radiating source. If you at the vertical azimuth pattern of the antenna it is more of a ring or vertically compressed donut. Granted the compression is not that much for a 2dBi antenna but is is not a sphere. Sorry again, said I was a nitpicker. The whole idea about increasing gain on a vertical dipole is to keep compressing the ring so that the vertical coverage angle is decreased, but the horizontal coverage radius is increased. Which means further distance.