RE: [Madwifi-users] Weather experience? From: Lie, Martin - 2004-05-27 07:28:24 ```For starter: RF is a large subject, and theory cannot always explain physical situations. Wether or not you can set up this link varies according to your regulatory domain and frequency. A better antenna may work, but it may not be legal. On such a distance you such also take into account the "ack timeout" (I don't know if this is adjustable in Madwifi) in order to get the 802.11 protocols running. If your card outputs 20 dBm and you are using a parabolic antenna with 23 dBi gain, you should in theory output 43 db from the antenna. You should also take into account the RF loss in cables, joints etc. (usually printed on the cables) if your card is not close to the antenna, or you have an excessive use of connectors and joints. Usually, you can subtract about 3 db for heavy rain, and about 7 db for heavy snow. Tables for this exists in large quantity (perhaps not on the net, though). For calculating the theoretical loss in vacuum line-of-sight, use the following formula: L = (20 log d) + (20 log F) + k where d=path length F=frequency in MHz k=constant depending on d: 32.4 if d is in km 35.58 if d is in miles L is the path loss in db. So, this theoretical model show us that for a 2.457 Ghz (ch 10) link with output power of 43 db, after 8 km the loss in db is 118. If the other end uses a similar parabolic antenna, you should add the gain of this antenna so that you can calculate the signal that reaches the RF reciever at the other end: Signal = 43 - 118 + 43 = -32 db. This is a strong signal and it should be possible to get 11 Mbit/s on this. Lets say there is heavy snow, your signal is still -39 db. The noise level usually is at about -90 db (depends on where you are). Of course, refractions and bad antennas may damage your signal. If you want a better analysis model, use the "Radio Mobile" program to take into account the different parameteres, terrain etc. http://www.cplus.org/rmw/english1.html Do anyone know how to set the ack timeout value in the madwifi driver? - Martin -----Original Message----- From: listas@... [mailto:listas@...] Sent: 26. mai 2004 20:13 To: madwifi-users@... Subject: [Madwifi-users] Weather experience? Importance: Normal Hi, Ive bougth two atheros based minipci cards (one from netgear and the other from mikrotik.com) as im looking forward linking two points at a 8km distance, with line of sight. Obviusly ill try to use the better antennas I can get, but the thing worryes me about is what could happen under humidity,rain or snow..does anyone has any pdf, or gnuplot graph showing delay, tcp rates under such conditions? Thanks in advance, Steve. ------------------------------------------------------- This SF.Net email is sponsored by: Oracle 10g Get certified on the hottest thing ever to hit the market... Oracle 10g. Take an Oracle 10g class now, and we'll give you the exam FREE. http://ads.osdn.com/?ad_id=3149&alloc_id=8166&op=click _______________________________________________ Madwifi-users mailing list Madwifi-users@... https://lists.sourceforge.net/lists/listinfo/madwifi-users ```
 Re: [Madwifi-users] Weather experience? From: Michael Renzmann - 2004-05-27 12:43:11 ```Hi. Lie, Martin wrote: > On such a distance you such also take into account the "ack timeout" (I > don't know if this is adjustable in Madwifi) in order to get the 802.11 > protocols running. Ack timeout is adjustable "out of the box" in WPA branch. If you use HEAD, you need to apply a patch, which is available here: http://sourceforge.net/tracker/index.php?func=detail&aid=961398&group_id=82936&atid=567755 In fact you should adjust slottime, ack-timeout and cts-timeout, not just one of these values. Bye, Mike ```