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[Ham-80211] May 2005 Followup on 4.4 mile link problem posted May 2004, Update January 2005

w3sz w3sz at comcast.net
Sun May 8 18:59:41 UTC 2005


Hello, All,

This is just a follow up to a post I made in May 2004, to relate the
solution of the problem.  I am hoping that it will help someone like those
of you on the list helped me!  I apologize if it it too long.

Last May I had posted to the list with a query and got very many helpful  
responses.

The gist of things was that I had just at that time set up a wireless link  
between two properties that are 4.4 [4 and 4 tenths] miles apart.  Both  
are on hilltops, and there is line of sight between the properties  
visually and confirmed by profiling the direct path between the properties  
using Topo USA,  except for for possibly a large oak tree that I can't  
remove at one end.

I used D-Link DWL 2100 AP's in Point to Point Bridge mode at both ends.  
Each unit was mounted in a weatherproof box at the back of a barbeque  
grill 24 dBi parabolic antenna set up for horizontal polarization.

I found that after optimizing things I could only get a thruput of 400Kbps  
or so, and I could only do that by blasting things in at 36 Mbps or so and  
getting retry rates in the 97% range or so.  My link budget said that I  
should be OK [17.9 dB thermal fade margin], but obviously I wasn't OK.

At that time many helpful suggestions were offered.  I wondered if perhaps  
the tree at one end was more obstructive than I had realized.  Nothing  
that I did improved the thruput, and when winter came and the trees became  
bare, thruput didn't improve AT ALL.

This January I ended up removing the D-Link units and replacing them with  
a Senao Wireless Multiclient Bridge at each end of link, running in  
Point-to-point bridge mode. set to 11 Mbps fixed speed.  With this I  
immediately got consistent 3.5-4 Mbps thruput with the tower most of the  
way down; before I had it all the way up to clear any potential but  
unappreciated obstruction! [link thruput checked using QCheck].  Now, the  
leaves are back on the trees, the tower is still not fully extended, and  
my link speeds remain at 3.5-4 Mbps.  So in my case the D-Link units were  
a real problem, and changing to the Senao units made a huge difference.   
The leafy trees and the other issues we all worried about were all 'red  
herrings', as it turns out.

I should also note that I was having major latency problems with the  
D-Link units that rendered some remote control software/hardware systems  
unworkable, and with the Senao units all of this now works as advertised,  
as well.  I hope this is of some help to someone on the list.

73,

Roger Rehr
W3SZ

-- 
Roger Rehr
W3SZ
http://www.qsl.net/w3sz




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