[MLB-WIRELESS] Calculating Antenna Range

[sanbar]

Very nice answer. Worth preserving on the melbwireless website somewhere?
- Barry

Michael Borthwick wrote:

> 
> I'm assuming if you want a single "antenna's range" as opposed to the maximum distance of the link between two
> antennas then what you have at the other end is an antenna with no gain ie the card itself.
> 
> This is all pretty cruisy:
> 
> 
> 
> You simply add up all the gains in the system and subtract all the losses including the path loss as the radio
> waves expand out from the antenna.
> 
> Assuming at the AP end you have an Orinoco with 15dBm output (from the spec sheet) + typical 8dbi omni antenna
> - pigtail loss of 1dB(say) = 22 dB total gain at the A.P. end
> 
> At the other end you are just wandering around with your laptop with inbuilt antenna so just have the gain of
> the radio itself ie 15dBm
> 
> Sooooooo:  the total gain for the link is 15+22=37dB woo hoo !
> 
> However you have path loss to contend with - simplifying the formula taken from Flickenger's Building
> Community Wireless Networks (O'Reilly 2002) the path loss equals 20 log(distance in miles) + 104
> 
> so lets say your links are 8K or 5 miles apart your loss is 118 dB over the link
> 
> Gains minus losses for the system as a whole = 37 - 118 = -81 dB
> 
> 
> The receiver sensitivity of the Orinoco silver from the manual is -82dB at 11MBps however you aren't out of
> the woods yet as it is recommended to have about 20dB headroom so in this case you are screwed. You cant
> connect at 11Mbps to an A.P. running an 8dBi omni antenna from 8 K's away with a standard card - which makes
> sense intuitively.
> 
> We need to find another 20dB somewhere. Stick a 24dBi parabolic at the other end and you are in business.
> Might get away with an 18dB in good conditions or if you are happy to run a lower data (the Silver is 12dB
> more sensitive at 1Mbps than 11Mbps which is still a lot faster than your modem).
> 
> I have ignored losses from long runs of cable and heaps of connectors - if your bag is playing with that stuff
> then you probaby have the skills to factor in the losses that will result.
> 


--

barry park
http://members.optushome.com.au/barrypark
-=all your http_get are belong to us=-


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