Which Antenna type

drainey

I just took the practice exam that came with my study guide and I have a couple of questions where the answers they give don't seem right. I won't give the question exactly due to copyright issues.

Their answer to the kind of antenna to use if two sites are 10 miles apart would be dipole, I was thinking for that distance you'd need highly directional.

The other answer was that a dipole antenna with higher gain would have greater vertical coverage. I was thinking that as the gain increased the wave would flatten and spread out making for less vertical coverage.

I'll look these up in my CWNA study guide from Planet3 at work tomorrow but I was wondering what you guys thought.

Thanks.

JDMurray

The most common 802.11 antennas are dipole. The little "rabbit ears" on wireless routers are two dipole antennas. They create an emission patterns in the shape of a donut. If you need point-to-multipoint communications from one station to many others, a 10-mile wide donut would be the best way to get the coverage. A Yagi or dish antenna would give you a tight, 10+ mile beam, but this is best for point-to-point links only. If the question was worded with the phrase "two sites 10 miles apart," I would have chosen a directional antenna myself.

drainey

Thanks JD. The question was basically which antenna would be best if you wanted to connect two sites 10 miles apart with mulitiple choice answers of dipole, directional, highly directional, or sattelite dish. With those choices and the 10 mile distance I figured highly directional to be the best choice. The test software came back with dipole as the answer. Of course in real life you'd have to take in other factors like LOS, weather, enviroment, etc.

Anyway thanks for the feedback.

JDMurray

The first thing that I think of with using dipoles over a 10-mile stretch is cost. A dipole at each point would typically be more inexpensive than two parabolic dishes. You also don't need to align dipoles like you would two dishes. The possible downside of dipoles is that each transmitter would need a greater power output than you'd need with dishes.

There is always a possibility that the answer in the wrong. Do you have the latest update for the practice test?

drainey

Thanks again for the feedback.

It took a while but I finally got that question to pop up again. It never states a point to point vs point to multipoint or really any other criteria. It simply asked which antenna type would be best to bridge a gap between two sites 10 miles apart. Therefore I believe you probably nailed it when you mention the lower cost of Dipoles and the fact that you don't need to align them as the reason for the answer dipole.

I'm taking the CWNA on May 11th so if you have any study tips besides the official study guide and test from the site that'd be great. I did pick up a CBT lab series that seems pretty good.

JDMurray

Besides the study guide, having actual hands-on experience installing 802.11 equipment, configuring the firmware, and troubleshooting basic connectivity problems helps considerably on the CWNA exam.

drainey

Thanks.

I do have some hands on. I have installed three point to point connections and two straight AP's here at work as well as various home wireless setups. I have gotten a fair share of troubleshooting one of those point to point connections as we had RF interference, a lightning strike, hail damage to an antenna, and duplex issues between one of the bridges and our switch. All at different times of course. But I switched the bridges from 802.11b to 802.11g and upgraded their firmware which eliminated our RF and duplex issues. The lightning strike and hail damage is just something to live with in Kansas but man what a mess. The lightning took out the bridge and both hubs at our remote site.

JDMurray

May I suggest lightning arrestors on your antenna cables? Ham radio people swear by them. And you might have a question that involves them on the CWNA exam too.

drainey

I actually have lightning arrestors in use on all antenna connections. The only thing I can think of is I didn't put the ground rod far enough into the ground the first time around. Either that or the lightning came in through some other route and jumped to the one of the hubs and backfed to the bridge. But that's not very likely. Anyway thanks for the help and advice.