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[Ham-80211] May 2005 Followup on 4.4 mile link problem posted May2004, Update January 2005

jeff at aerodata.net jeff at aerodata.net
Mon May 9 15:59:43 UTC 2005

Other then of course signal strength, it sounds like it could have been a
802.11b timing issue. Not sure what that is called, but I have heard on
certain units on links over 1.5 miles or so, you can get timeouts due to
the propagation delay.

> 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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