I have a question regarding the 24dBi 2.4GHz Wire Grid antenna. What kind of range does this antenna have when hooked up to a Linksys WRT54G wireless router? The reason I ask is, I don't have a DSL connection where I live but my neighbor down the road does, he lives 1.5miles from me. However there is a line of trees in the way down the road, and I can't get the antennas placed over the tree line, just slightly below the tree line. Just using 2 of these antennas and say 2 Linksys WRt54G wireless routers, can I make the link? Or do I need to add a power booster to each end? If so how much power and what is the FCC legal limit on this I have no idea?
Thanks, Joey
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Well, I think there's enough info to run the calculations. What's missing is where the WRT54G routers are mounted. On the antennas or inside the house. I'll assume that you're going to build an outdoor enclosure (NEMA box) and hang it on the back of the dish.
See Link Calcs at:
What we have is: TX power +15 dBm TX coax loss 4 dB (3 ft LMR-240 plus a mess of connectors) TX ant gain +24 dBm Distance 1.5 miles RX ant gain +24 dBm RX coax loss 4 dB (3 ft LMR-240 plus a mess of connectors) RX sens -84 dBm (at 12Mbits/sec connection) Fade margin unknown Under ideal conditions, this give you 6Mbits/sec thruput which should be more than enough for your DSL connection. If you happen to have a
6Mbit/sec DSL connection, or want to go faster, then the receiver sensitivity will need to be adjusted according to the table at:
The idea is to obtain a fade margin (or System Operating Margin) of at least 20dB. This is directly related to the overall system reliability. See the table at the above URL.
Plugging the values into:
I get a fade margin of 31.3dB which is quite good.
However, don't get all excited quite yet. This is the *BEST* case calculation. Reality and conspiracy will reduce this considerably.
You must have objects along the line of sight be outside the Fresnel Zone:
That's about 23 ft radius at midpoint. So, the dishes at the end points should be at least 23 ft above the ground. In addition, you need a 23ft clearance around the line of sight at midpoint. Do you have that? If the trees are at midpoint, you don't.
The line of trees are going to be a BIG problem. You didn't specify if they are dense or thin or how deep. Folliage attenuation can be estimated but I need data. In general, if you can see through the trees consistently, especially at trunk level, then you have a chance. Even so, you're going to have attenutation. You have about 10dB. Lose it wisely.
Ooops. I forgot to mumble something about the rules-n-regs.
Point to Point wireless is handled quite differently from point to multipoint. With point to multipoint, the maximum tx power is 1 watt (+30dBm) into a 6dBi omni antenna. For point to point, the power limit can be reduced by 1dB for every 2dB increase in antenna gain. Handy table: xmit antenna EIRP EIRP power gain +dbm +dbi +dbm watts 30 6 36 4 29 9 38 6.3 28 12 40 10 27 15 42 16 26 18 44 25 25 21 46 40 24 24 48 63
So, with a 24dBi gain dish, you can crank out +24dBm (250mw) which is well above what the WRT54G can safely transmit. You're legal.
It depends on the dB rating of the antenna at both ends. The best antennas are parabolic and are rated above 22dB.
Absolutely not. Line of sight is critical at these frequencies and it doesn't mean almost. In fact, there's a zone around the line of sight that can't be infringed. The longer the distance, the larger the zone.
Any power booster added to unlicensed consumer gear will a) in almost every circumstance be illegal, and b) won't do anything except annoy the people around you.
If you want to know how much distance your antennas can cover _with_ line of sight, start here
formatting link
and use the simple calculations.
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