passive reflectors

[Tomasz Ciolek]

Does the quipment in the link re-generate the signal at the dishes? is
the repeater powered?

regards
Tomasz Ciolek

On Sun, Jun 09, 2002 at 07:03:07PM -0400, Tony  wrote:
> Robert
> I think you need to get out and try this yourself :) Coming from a
> background of doing licensed link this can me done. While this will not
> work in all cases, if does work for shorter link. Using ISM equipment we
> have made this work at 3 mile.
> 
> Sincerely
> Tony 
> 
> -----Original Message-----
> From: wireless-admin at lists.samba.org
> [mailto:wireless-admin at lists.samba.org] On Behalf Of robert scholten
> Sent: Sunday, June 09, 2002 6:02 PM
> To: wireless at lists.samba.org
> Cc: eqeeu at yahoo.com
> Subject: passive reflectors
> 
> 
> This passive reflector stuff is baloney.  It's basic inverse-square law.
> Consider a setup with 2 dishes, e.g. 24dB Conifers.  Beam widths are 7.5
> and 10 degrees (-3dB widths).  Area is about 0.5m^2.
> Imagine you have a really good link with two 24dB dishes over 5 miles =
> 8km.  Let's say you get 1 nanowatt (i.e. -60dBm).  I've managed about
> -80dBm from a good site with two 24dB dishes, one site on the side of a
> small mountain, the other on the plains, length about 20km.  That
> translates to -73dBm for 8km, but let's be generous to Cringely.
> Now let's put a passive reflector at that point, instead of a single
> dish.  I.e. a reflector consisting not of Pringles tins, but good 24dB
> dishes with zero loss cable between them.  Ignore the fact that both
> dishes in the reflector will radiate (i.e. instant 3dB loss).  So the
> second dish re-radiates 1nW of power into a "cone" of 7.5 x 10 degrees.
> That power is spread over an area of approx. d*tan(a1)*tan(a2) where a1
> and a2 are the angles, 7.5 and 10 degrees.  At 1000m (again, let's be
> generous to Cringely and assume 1.5 miles is 1000m!).  The power is
> spread into 23000m^2 so at our final 24dB dish we have 0.5/23000 * 1nW =
> 2e-14 watts, or about -107dBm.  More realistically you should use -73dBm
> at the repeater, include at least 3dB loss in the repeater, add another
> 3dB because he's 1.5 miles away from the mountain (2km), and come up
> with a very optimistic -119dBm.  The best cards (Cisco 350's) are good
> down to about -94dB so it's pretty much irrelevant anyway.
> How big would Cringely's pringles tins need to be to make it work?
> Optimistically he'd need an extra 11dB, i.e. 5dB on each side, so 30dB
> (about 1.5m^2).  More realistically he'd be needing a good 25dB, 12.5dB
> per side, 9m^2.  Dishes of 3.4 m diameter (about 11 feet).
> Forget it!
> 
> 
> 
> To: Eqeeu <eqeeu at yahoo.com>
> Cc: wireless at lists.samba.org
> Subject: Piercing a mountain? Help!
> 
> 
> Eqeeu writes:
>  > Hi
>  > 
>  > I want to setup a 802.11b link between my house and a
>  > friends, the only problem is that there is a large
>  > mountain (I think its Ainslie mountain) smack in the
>  > middle of our two houses and its impossible to get
>  > line of site.
>  > 
>  > Is this a problem?
>  > 
>  > Would we have to go around or over the mountain with
>  > an extra repeater WAP somewhere, or is it possible to
>  > use two high gain 24dBi+ directional antenna and
>  > "pierce" straight through the centre of the mountain?
>  > 
> 
> 
> An article on doing passive repeaters is at :
> 
> 
>  http://www.pbs.org/cringely/pulpit/pulpit20020207.html.
> 
> 
> I think you can get more doco. from there.
> 
> 
> wes
> 
> 
> 
> 
> Do You Yahoo!?
> Sign-up for Video Highlights of 2002 FIFA World Cup

-- 
Tomasz M. Ciolek	*
			* 	Everything falls under the law of change;	
<tmc at dreamcraft.com.au>	*	  Like a dream, a phantom, a bubble, a shadow,
<tmc at goldweb.com.au>	*	  like dew of flash of lightning.
			*	  You should contemplate like this. 
*******************************************************************************
GPG Key ID: 0x7A18E49D	*	Available on www.pgp.net
*******************************************************************************