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G0FTD > WLAN 27.09.03 18:21l 43 Lines 1235 Bytes #999 (0) @ WW
BID : EA2088G0FTD
Read: GUEST OE5TUN DB0FHN OE5RCO DK8TQ DK5RAS DO1SLP DO6NP
Subj: 2.4Ghz rx sensitivity.
Path: DB0FHN<DB0RGB<DB0MRW<OK0PKL<OK0PPL<DB0RES<ON0AR<VK6HGR<KD7HAH<GB7LGS<
GB7TUT<GB7CIP<GB7SXE
Sent: 030927/1545Z @:GB7SXE.#38.GBR.EU #:18253 [Hastings] FBB7.00i $:EA2088G0FT
From: G0FTD@GB7SXE.#38.GBR.EU
To : WLAN@WW
I've been looking on the internet for information about WLAN rx sensitivity.
From the specifications of available hardware it appears that -80dbm or better
at the receiver is needed.
So just for fun lets have a look at a few figures.
Assuming at this stage unity gain antennas at each end and an ERP of 1 watt
you would have at the rx (after calculating free space path loss) a signal
level of -79.5dbm at a distance of exactly 3Km.
Here's a list of power levels vs distance assuming 1 watt o/p and dipoles.
1Km = -70dbm
2km = -76dbm
3km = -79.5dbm
4km = -82dbm
5km = -84dbm
6km = -85.6dbm
10km = -90dbm
15km = -93.5dbm
20km = -96dbm
25Km = -98dbm
30km = -99.5dbm
40km = -102dbm
If both antennas were at a height of 10 metres an unobstructed then your
maximum range would be 26Km no matter what power you had ! At 26km we can see
that we could reasonably expect -99dbm at the receiver input.
So an antenna of at least 20db power gain would be required for the link to
work with a typical rx with -80dbm sensitivity.
These figures assume an ideal world, but will vary according to antenna gains
used, the individual output powers at each end, local scatter effects etc.
- Andy -
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