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<DIV><FONT face=Verdana size=2>Jason</FONT></DIV>
<DIV><FONT face=Verdana size=2></FONT> </DIV>
<DIV><FONT face=Verdana size=2>how far in distance was the link...</FONT></DIV>
<DIV><FONT face=Verdana size=2></FONT> </DIV>
<DIV><FONT face=Verdana size=2>Matt</FONT></DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=jtedesco@request.com.au href="mailto:jtedesco@request.com.au">Jason
Tedesco</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=agmcom@bigpond.com
href="mailto:agmcom@bigpond.com">Glenn Cook</A> ; <A
title=melbwireless@wireless.org.au
href="mailto:melbwireless@wireless.org.au">melbwireless@wireless.org.au</A> ;
<A title=clae@tpg.com.au href="file://clae@tpg.com.au">Clae</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, May 29, 2003 11:34
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: [MLB-WIRELESS] hops over
water</DIV>
<DIV><BR></DIV>I did have a link going over water from Werribee South to Port
Arlington. The equipment used was two 25db grids at each end.
Looking at net stumbler the link was relatively strong. <BR><BR>Although
throughput of data was dreadful, although I think this was due to the hop I
was routed to.<BR><BR>I've currently just removed my AP from my mast, and am
installing a Linux box in my roof, so I can let you know how the signal is
once everything is set up again.<BR><BR><BR>Link below of view across the
bay.<BR><A
href="http://www.jason.id.au/wifi/slides/DV00026.html">http://www.jason.id.au/wifi/slides/DV00026.html</A><BR><BR>>
-----Original Message-----<BR>> From: Glenn Cook
[mailto:agmcom@bigpond.com]<BR>> Sent: Wednesday, 28 May 2003 20:14<BR>>
To: <A
href="mailto:melbwireless@wireless.org.au">melbwireless@wireless.org.au</A>;
Clae<BR>> Subject: Re: [MLB-WIRELESS] hops over water<BR>> <BR>>
<BR>> I installed a radio link between Bourke Place and Woolstores <BR>>
(Geelong) for<BR>> Deakin Uni a few years ago.<BR>> <BR>> It was a 7
Ghz, 34 Mbps space diversity link.<BR>> <BR>> And yes, water can be an
absolute pain to get a link over.<BR>> <BR>> Glenn<BR>> <BR>>
----- Original Message -----<BR>> From: "Clae" <<A
href="mailto:clae@tpg.com.au">clae@tpg.com.au</A>><BR>> To: <<A
href="mailto:melbwireless@wireless.org.au">melbwireless@wireless.org.au</A>><BR>>
Sent: Tuesday, May 27, 2003 6:10 AM<BR>> Subject: [MLB-WIRELESS] hops over
water<BR>> <BR>> <BR>> From the wireless-longhaul list.<BR>>
<BR>> The idea of links over water has been discussed previously on MW
to<BR>> link areas surrounding Port Phillip Bay. I believe there is
one such<BR>> link functioning in the Williamstown area.<BR>> <BR>>
The following discussion covers technical aspects of these links,<BR>>
problems encountered, and how to get the best results, from people<BR>> who
have actually done this.<BR>> <BR>> Clae.<BR>> <BR>> /some
snipping for brevity/<BR>> <BR>> >Date: Sun, 25 May 2003 16:11:22
-0700<BR>> >From: Tim Pozar <<A
href="mailto:pozar@lns.com">pozar@lns.com</A>><BR>> ><BR>> >On
Sun, May 25, 2003 at 07:06:18PM -0400, S Woodside wrote:<BR>>
>> On Saturday, May 24, 2003, at 11:45 PM, Ben Johns
wrote:<BR>> >> > Has anyone on the list done something
similar? I'm <BR>> interested to know<BR>> >> >
how<BR>> >> > ocean/sea could affect a signal. The water is
pretty <BR>> calm most of the<BR>> >> > time, sheltered
by the islands/reefs, but could <BR>> reflection/refraction<BR>>
>> > still have an effect?<BR>> >> ><BR>>
>> I remember reading about a link over water, at a nature
preserve I<BR>> >> think over a lake. IIRC the polarization
made a difference, don't<BR>> >> remember which way was better
though.<BR>> ><BR>> >You want to be vertically polarized to
minimize the horizontal<BR>> >polarized signals from the water.<BR>>
><BR>> >Tim<BR>> >------------------------------<BR>>
><BR>> >Message: 3<BR>> >Date: Sun, 25 May 2003 13:47:10
+0700<BR>> >From: Stefan Probst <<A
href="mailto:stefan.probst@opticom.v-nam.net">stefan.probst@opticom.v-nam.net</A>><BR>>
><BR>> >At 13:45 25.05.2003 +1000, you wrote:<BR>>
>-------------------------<BR>> > >Has anyone on the list
done something similar?<BR>> ><BR>> >I was line-up engineer for a
4.7 GHz radio link over wet <BR>> (wet rice fields)<BR>> >and water
terrain.<BR>> ><BR>> >The problem is, that you are very likely to
get reflection <BR>> from the water<BR>> >and from air layers of
different humidity above the water, caused by<BR>> >temperature
differences. The result is, that you get at the <BR>> receiving
side<BR>> >not only the direct signal, but also the reflected one. The
<BR>> reflected one<BR>> >has to travel a longer distance and is
therefore delayed, i.e. phase<BR>> >shifted, with the original at the
receiving antenna. Depending on the<BR>> >distance, the phases will be
in sync, i.e. the signal gets <BR>> stronger. If it<BR>> >is 180f out
of sync, the both signals will be subtracted, <BR>> i.e. get much<BR>>
>weaker, or can even disappear. Since this is not a constant, <BR>> and
not a<BR>> >single reflection, the result is, that the signal strength
<BR>> fluctuates. The<BR>> >result is known as "fading".<BR>>
><BR>> >Solutions:<BR>> >- Very, very highly directional
antennas that shield the <BR>> reflected signal.<BR>>
> Usually only feasible over short links and high towers,
<BR>> i.e. if there<BR>> is<BR>> > a sufficient
large angle between the direct and the <BR>> reflected signal.<BR>>
>- If you are lucky, you can chose a signal path that has a natural<BR>>
obstacle,<BR>> > like a mountain, in such a way that
it shields the reflected<BR>> >signal from the<BR>>
> receiving antenna.<BR>> >- Frequency Diversity:
Since the phase difference depends on <BR>> the frequency,<BR>>
> there are good chances, that in case the resulting
<BR>> receive level on one<BR>> >frequency<BR>>
> is different from another frequency.<BR>>
> Means: The signal is transmitted simultaneously on two
different<BR>> >frequencies.<BR>> > When the bit
error rate exceeds a certain level on the <BR>> receiving side,<BR>>
the<BR>> > receiver would quickly switch over and take
the signal <BR>> from the other<BR>> >
frequency.<BR>> >- Space Diversity: The signal is received by two
antennas, <BR>> that are mounted<BR>> > with a
certain distance above each other.<BR>> > The
reflected signal changes at the two antennas, it <BR>> will sometimes
add<BR>> > "in phase", sometimes completely "out of
phase", i.e. <BR>> cancelling the<BR>> direct<BR>>
> signal. By choosing an appropriate distance (there are
<BR>> some ways to<BR>> >determine<BR>> >
it), it is possible to minimize the likelihood, that there is a<BR>>
>cancellation<BR>> > at both antennas at the same
time. The receiver will <BR>> choose the antenna<BR>>
> with the best signal. (Well, in fact there are two
receivers and<BR>> >a circuitry<BR>> >
determines which signal to choose).<BR>> > Space
diversity if often also used with wireless <BR>> microphones, high<BR>>
quality<BR>> > cordless phones, WiFi base
stations.<BR>> > As a modification (or in addition),
you can save the second<BR>> >receiver and the<BR>>
> switch-over circuitry by combining the signal of both
<BR>> antennas in such<BR>> a<BR>> >way,<BR>>
> that the direct signal is "in phase".<BR>>
> This means usually to add some extra RF cable length to
the lower<BR>> antenna,<BR>> > so that both cables
are same long. By this, the direct <BR>> signal adds<BR>> always<BR>>
> correctly. The reflected signal will be different, and
sometimes<BR>> >"in phase",<BR>> > sometimes
"out of phase". Only if it is "out of phase" <BR>> at both antennas<BR>>
> would the signal be completely lost. You should be able
<BR>> to increase the<BR>> > effect by creating an
array of several antennas above each other.<BR>> >In reality, Space and
Frequency Diversion is often used at <BR>> the same time.<BR>>
><BR>> >Good Luck!<BR>> ><BR>> >Stefan<BR>>
><BR>> ><BR>> >------------------------------<BR>>
><BR>> >Message: 4<BR>> >Date: Mon, 26 May 2003 10:39:34 +1000
(EST)<BR>> >From: "Ben Johns" <<A
href="mailto:benj@marinanet.com.au">benj@marinanet.com.au</A>><BR>>
><BR>> >As Stefan Probst has recommended, I will be using two
<BR>> antennae on each end<BR>> >of a link for space diversity.
Although I would like to know <BR>> if having the<BR>> >two antennae
set to different polarizations is of any <BR>> benefit. Ie, have<BR>>
>one set to horizontal and the other to vertical. Or should I <BR>> just
have<BR>> >them both set to vertical?<BR>> ><BR>>
>--<BR>> >Regards,<BR>> ><BR>> >Ben Johns<BR>>
><BR>> >------------------------------<BR>> ><BR>>
>Message: 5<BR>> >Date: Sun, 25 May 2003 18:22:05 -0700<BR>>
>From: <A
href="mailto:constantinos@shaw.ca">constantinos@shaw.ca</A><BR>>
><BR>> >We have a 23 mile link going over a strait of ocean. As
long as you<BR>> >have enough power, your high enough so the fresnel
zone is clear,<BR>> >good LOS, you should be good to go.<BR>>
><BR>> >Cheers,<BR>> ><BR>> >Constantinos
Tsakonas<BR>> >www.constantinos.ca<BR>> ><BR>>
>------------------------------<BR>> ><BR>> >Message: 6<BR>>
>Date: Mon, 26 May 2003 08:44:51 +0700<BR>> >From: Stefan Probst
<<A
href="mailto:stefan.probst@opticom.v-nam.net">stefan.probst@opticom.v-nam.net</A>><BR>>
><BR>> >At 10:39 26.05.2003 +1000, you wrote:<BR>>
>-------------------------<BR>> >>As Stefan Probst has
recommended, I will be using two <BR>> antennae on each end<BR>>
>>of a link for space diversity. Although I would like to <BR>> know
if having the<BR>> >>two antennae set to different polarizations is
of any <BR>> benefit. Ie, have<BR>> >>one set to horizontal and
the other to vertical. Or should <BR>> I just have<BR>> >>them
both set to vertical?<BR>> ><BR>> >My tip:<BR>> >Try, try,
try.<BR>> >Usually, it should both be vertical. But there are sometimes
<BR>> crazy effects.<BR>> ><BR>> >I would even start with one
antenna. Maybe it is enough. I <BR>> guess that in<BR>> >colder
climate fading over water is not such a problem like <BR>> in tropical
and<BR>> >subtropical areas like here.<BR>> >If one antenna is not
enough, try the second one and observe the<BR>> difference.<BR>>
>Maybe you find somewhere on the Web a way on how to <BR>> determine the
best<BR>> >height difference.<BR>> ><BR>> >And be prepared
that things change over time, with seasonal <BR>> changes of the<BR>>
>weather.<BR>> ><BR>> >Also, the thing with the two
"electrically same long" <BR>> antenna cables sounds<BR>> >a bit
easier than it is. Depending on the type of antenna <BR>> mast etc.,
the<BR>> >lower antenna (where the mast is often thicker) might be
<BR>> some cm "closer"<BR>> >to the sending antenna. The result was,
that I usually had <BR>> to find the<BR>> >right additional cable
length empirically, i.e. try <BR>> different additions and<BR>>
>observe the level of the received signal. This can be done <BR>> of
course only<BR>> >during daytimes with little fading....<BR>>
><BR>> >Good Luck!<BR>> ><BR>> >Stefan<BR>>
><BR>> >------------------------------<BR>> ><BR>>
>Message: 8<BR>> >Date: Sun, 25 May 2003 18:17:45 -0700 (PDT)<BR>>
>From: Michael Przybylski <<A
href="mailto:mikep@core.ucsd.edu">mikep@core.ucsd.edu</A>><BR>>
><BR>> >Another standard trick I have heard of to minimize
reflections with<BR>> >over-water links is positioning one antenna high,
the other one low.<BR>> ><BR>> >Regards,<BR>> >Mike
Przybylski<BR>> ><BR>> <BR>> --<BR>> "Our earth is degenerate
in these latter days; bribery and corruption<BR>> are common; children no
longer obey their parents; and the end of the<BR>> world is evidently
approaching." -- Assyrian clay tablet 2800 B.C.<BR>> <BR>> To
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