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<DIV><SPAN class=230480305-30052003><FONT face=Arial color=#0000ff
size=2>Matt, </FONT></SPAN></DIV>
<DIV><SPAN class=230480305-30052003><FONT face=Arial color=#0000ff
size=2> Sorry to say I have no idea how long the point to
point link is over the water. I should so some research, and check an
on-line map. I think it will be approx 10 to
20km's.</FONT></SPAN></DIV>
<DIV><SPAN class=230480305-30052003></SPAN><SPAN class=230480305-30052003><FONT
face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=230480305-30052003><FONT face=Arial color=#0000ff size=2>#
jason</FONT></SPAN></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> Matthew Hill
[mailto:matthew.hill@matthewhillonline.com]<BR><B>Sent:</B> Thursday, 29 May
2003 12:07<BR><B>To:</B> Melbourne Wireless<BR><B>Subject:</B> Re:
[MLB-WIRELESS] hops over water<BR><BR></FONT></DIV>
<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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