Hilly,
The short answer is No, you really need clear line of sight.
The long answer is Yes, there are many exceptions to the rule if you are prepared to put in the hard graft and tweak things so as to get the best signal. Also the amount of money you invest in antennas and gear can impac the link capabilities.
Jus tto show you how much here is a good example.
On a 14dBi antenna facing out network from 15km away just clipping the top of Mt Wellington and shooting through a tree i do not get any signal on the $100.00 Orinoco rebrand card. Exactly the same setup with one of the more expensive Senao cards i get a great signal and even a noce connection.
The argument is that the senao is a 200mw card, however wat you must realise is that when using netstumbler you are using the receive capability of the card more than the send.
I also have 2 connections that are not what i would call clear line of sight going over 1.5km and have a prety stable connection between them. The trick with this one was to use the waveguides and capitalise on the ability to use a bouonced signal.
Andrew
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but I am on about the highest point on the coast(apparently), so should be ok for most people. 
Linear Mode
