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mperdue
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Antani, Power and freqency

Thu Nov 17, 2005 9:11 pm

Is it correct to say that a higher db omni will have a longer range than a lower db omni. However the higher the db the flater the cone will be. And thus using a lower db omni will be shorter range but have better non-line of sight chacteristics?

Is it correct to say that a sr5 card using 802.11a at 5.8ghz will transmit at 400mw? but if you lower the frequency to 5.1 that the power of the card is reduced?

If the above statement is true, then does the 65mw cards have the same chacteristics? if it's 65mw at 5.8 and you drop down to 5.1 the power is reduced? And by what amount is it reduced?

What would I gain by switching my 802.11b clients to g?

Thanks!
Michael
 
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dwright
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Re: Antani, Power and freqency

Fri Nov 18, 2005 8:57 pm

Is it correct to say that a higher db omni will have a longer range than a lower db omni. However the higher the db the flater the cone will be. And thus using a lower db omni will be shorter range but have better non-line of sight chacteristics?
Not sure about the better non-line of sight characteristics but a higher db omni has a flatter rf propagation. Think of it like this. hi db=pancake, low db=doughnut. With a higher power omni, depending on the height that it is installed could potentially shoot the signal over your customers. Look at the antenna pattern data sheets of the antenna to determine your signal coverage area.
Is it correct to say that a sr5 card using 802.11a at 5.8ghz will transmit at 400mw? but if you lower the frequency to 5.1 that the power of the card is reduced?
Take a look at the SR5 data sheet According to it, the only thing that changes the output is the data rate that it is transmitting on. I can not confirm whether or not frequency has anything to do with card output. I do know that the different frequencies in the 5Ghz band do have different EIRP limits.
If the above statement is true, then does the 65mw cards have the same chacteristics? if it's 65mw at 5.8 and you drop down to 5.1 the power is reduced? And by what amount is it reduced?
Again, take a look at the Specifications Same principal as the SR5 appears to apply with the CM9.
What would I gain by switching my 802.11b clients to g?
A headache? Do to the fact that 11G joins to adjacent 11B channels together, you have less overlapping channels, and are most likely either going to see more noise, or interfer with yourself. 11G uses OFDM so it is better when using it in an urban enviroment where signals bouncing off of buildings produce multipath. 11G IMHO is an indoor protocol.

Dan
 
mperdue
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Mon Nov 21, 2005 5:15 pm

Thank you for your comments.

As for using 802.11b. I am having pretty good success with my two repeater sites. I have 20-25 connections on a single site using a 18db omni with 3 degree downtilt over the town. I even have several links shooting through trees but they are fairly close to the antani. But I have a couple of longer links of about 4 miles (including my home) which is surrounded through trees. I'd like to find a way to get them connected but really just looks like I need to forget the idea and just setup another LOS repeater.

The other issue is that the links to these repeaters sites is on 5G. And while the one from my office to the tower seems to be fine, when I try to setup the third link which is twice as far (4 miles) it's a very weak and almost non-existant signal. I'm using the 65mw cards, the tower unit uses a 8db 5ghz omni. And the far end.. i've tried using omni, yagi, several directionals. The only directional I can get to work is a 30db unit. And that didn't even work untill I replaced a 10ft cable with a 25ft cable (guess the short one is bad).

One of the antai vendors told me that at 5.2ghz i'm not goign to get 400mw out of the sr5 cards that I just ordered. Said I had to go to 5.8ghz. so i'm confused yet again. I just don't think I need 400mw to shoot 5.5 miles LOS. I was goign to try it at 200mw and get separate radios and give that a try now.

-Michael
 
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jp
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power

Mon Nov 28, 2005 5:36 am

Thank you for your comments.

One of the antai vendors told me that at 5.2ghz i'm not goign to get 400mw out of the sr5 cards that I just ordered. Said I had to go to 5.8ghz. so i'm confused yet again. I just don't think I need 400mw to shoot 5.5 miles LOS. I was goign to try it at 200mw and get separate radios and give that a try now.

-Michael
In the US, it is not legal to use the same higher power rules that apply to 5.8ghz in the 5.2ghz range. Power (and range) is greatly diminished in the 5.2 range as a result. Read up on fcc rules if you are in the US.

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