[MLB-WIRELESS] Melbwireless Digest, Vol 37, Issue 12

Fri Oct 31 17:17:26 EST 2008

my node, JTQ, has a good LOS to point cook and a possible LOS to JEE
with a 3m mast. im situated on the bay down in beaumaris.

On Fri, Oct 31, 2008 at 12:00 PM,  <melbwireless-request at wireless.org.au> wrote:
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> Today's Topics:
>
>   1. Long distance links (mw at freenet.net.au)
>   2. Re: Long distance links (mw at freenet.net.au)
>   3. Re: Long distance links (Ben Balbo)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 30 Oct 2008 22:26:32 +1100
> From: <mw at freenet.net.au>
> Subject: [MLB-WIRELESS] Long distance links
> To: <melbwireless at wireless.org.au>
> Message-ID: <0CE5BA63CBF543608C4920F3BA1EE90A at viewbankrise.net.au>
> Content-Type: text/plain;       charset="us-ascii"
>
> Hi Folks,
>
> I have been thinking about how to set up a second Geelong<->Melbourne link,
> and have considered a few options.
>
> One idea is to set up a half-way point somewhere, and I found a prospective
> spot in portarlington that looked very good.  I have this kit (like I
> brought to the last meeting) made up of Mikrotik Crossroads
> (http://shop.duxtel.com.au/product_info.php?products_id=45) and commTenna
> (http://shop.duxtel.com.au/product_info.php?products_id=46) which from my
> loungeroom window, I could connect to the hotspot service at the caravan
> park at Portarlington foreshore.  I have a friend whi lives a few blocks
> away, and the lay of the land looked perfect to get a bead on my place back
> the other way.
>
> Unfortunately I was defeated by trees (!) and my buddy there isn't willing
> to set up a pole on his roof, so I'm back to square 1.
>
> So I'm still on the lookout for some intermediary location - if there's
> anyone with a look over the bay to geelong (check out node KBN
> http://www.melbournewireless.org.au/maps/view?id=KBN) I'd like to hear from
> you.
>
> For distances greater than about 25Km, I have a plan that should work well
> and still keep us insidethe legal transmission limits too.
>
> As you all know, I'm sure, we can't go over 36dB EIRP (4W) so with a 600mW
> radio, and maybe a cable loss of 2, we can only use a antenna:  28dBm radio
> - 2dBi cable loss + 10dBi antenna = 36 (and a 400mW radio will need 12dBi
> antenna, right?)
>
> Now according to my calculations, if we have a receive sensitivity of -93 at
> the other end of a transmitter running at max output, then we can only get
> about 25Km before we run out of signal.  If we wanted to go 50Km, then we
> need a receiver with an antenna gain of up around the 24dBi mark, which, of
> course, ends up producing 46dB EIRP on the transmit cycle - oops, over
> limit!
>
> Ok, so I'm telling you what you already know I s'pose, so I'll get to the
> point! ;-)
>
> These Mikrotik devices that I use are able to use the two antenna
> connections to transmit on one and receive on the other.  That means that if
> the receive antenna is connected to a 24dBi grid antenna and the transmit
> antenna has just a 12dBi panel or something, then we should be able to get a
> nice solid long distance link happening, and keep within the legal limits no
> probs!
>
> Now, there's also the other issue that affects stability of a Melb-Geelong
> link, and that's the bay.  Most of you probably also know that when shooting
> over water, relfections from the surface can end up causing interference on
> the direct transmissions, especially when the path between the two antennas
> is exactly a half wavelength longer (or 1.5, 2.5, ... etc) than the
> reflected path - thus cancelling out the signal waveforms.
>
> So you probably also know that two antennas set up the right distance apart
> will help overcome this effect using the default diversity switch mode, but
> if we use the above technique to have two antennas with different gains,
> then we run into EIRP limit troubles again.
>
> There *is* a solution! ;-)
>
> Once again, the Mikrotik systems come to the rescue with a special 'Nstreme
> Dual' mode.  In this mode, a router with two radios installed can be set up
> to transmit on one radio and receive on the other.  The usual benefit of
> this technique is to get a full duplex radio link, but the other cool
> benefit is that we can also use dual high gain antennas on the receive
> circuit for diversity, and one (or two) lower gain antennas on the transmit.
>
> Sound cool?  I sure think so :-)
>
> So anyone interested in some experimentation?  I'm quite keen to give it a
> go, and I'll even help you out by offering some of this gear at or below
> cost.  If you're game, let me know - on or off list is fine by me :)
>
> Cheers!
>
>
>
> ------------------------------
>
> Message: 2
> Date: Thu, 30 Oct 2008 22:50:31 +1100
> From: <mw at freenet.net.au>
> Subject: Re: [MLB-WIRELESS] Long distance links
> To: <melbwireless at wireless.org.au>
> Message-ID: <D1DD05101D0E4E42BE1B4A882A3F87E7 at viewbankrise.net.au>
> Content-Type: text/plain;       charset="us-ascii"
>
> Just wanted to clarify a couple of points after reading that over again :-}
>
> It's not ME that has the 'other' melb-geelog link, of course, but it kinda
> looks like I'm suggesting that in the first sentence ;-)  That's Peter's
> link, and how it is set up: I have no idea (but I'd like to talk about
> it!:-)
>
> Secondly, that's 100Km in my discussion about the 24dBi antenna, not 50Km!
>
> Cheers!
>
>> -----Original Message-----
>> From: melbwireless-bounces at wireless.org.au
>> [mailto:melbwireless-bounces at wireless.org.au] On Behalf Of
>> mw at freenet.net.au
>> Sent: Thursday, 30 October 2008 10:27 PM
>> To: melbwireless at wireless.org.au
>> Subject: [MLB-WIRELESS] Long distance links
>>
>> Hi Folks,
>>
>> I have been thinking about how to set up a second
>> Geelong<->Melbourne link, and have considered a few options.
>>
>> One idea is to set up a half-way point somewhere, and I found
>> a prospective spot in portarlington that looked very good.  I
>> have this kit (like I brought to the last meeting) made up of
>> Mikrotik Crossroads
>> (http://shop.duxtel.com.au/product_info.php?products_id=45)
>> and commTenna
>> (http://shop.duxtel.com.au/product_info.php?products_id=46)
>> which from my loungeroom window, I could connect to the
>> hotspot service at the caravan park at Portarlington
>> foreshore.  I have a friend whi lives a few blocks away, and
>> the lay of the land looked perfect to get a bead on my place
>> back the other way.
>>
>> Unfortunately I was defeated by trees (!) and my buddy there
>> isn't willing to set up a pole on his roof, so I'm back to square 1.
>>
>> So I'm still on the lookout for some intermediary location -
>> if there's anyone with a look over the bay to geelong (check
>> out node KBN
>> http://www.melbournewireless.org.au/maps/view?id=KBN) I'd
>> like to hear from you.
>>
>> For distances greater than about 25Km, I have a plan that
>> should work well and still keep us insidethe legal
>> transmission limits too.
>>
>> As you all know, I'm sure, we can't go over 36dB EIRP (4W) so
>> with a 600mW radio, and maybe a cable loss of 2, we can only
>> use a antenna:  28dBm radio
>> - 2dBi cable loss + 10dBi antenna = 36 (and a 400mW radio
>> will need 12dBi antenna, right?)
>>
>> Now according to my calculations, if we have a receive
>> sensitivity of -93 at the other end of a transmitter running
>> at max output, then we can only get about 25Km before we run
>> out of signal.  If we wanted to go 50Km, then we need a
>> receiver with an antenna gain of up around the 24dBi mark,
>> which, of course, ends up producing 46dB EIRP on the transmit
>> cycle - oops, over limit!
>>
>> Ok, so I'm telling you what you already know I s'pose, so
>> I'll get to the point! ;-)
>>
>> These Mikrotik devices that I use are able to use the two
>> antenna connections to transmit on one and receive on the
>> other.  That means that if the receive antenna is connected
>> to a 24dBi grid antenna and the transmit antenna has just a
>> 12dBi panel or something, then we should be able to get a
>> nice solid long distance link happening, and keep within the
>> legal limits no probs!
>>
>> Now, there's also the other issue that affects stability of a
>> Melb-Geelong link, and that's the bay.  Most of you probably
>> also know that when shooting over water, relfections from the
>> surface can end up causing interference on the direct
>> transmissions, especially when the path between the two
>> antennas is exactly a half wavelength longer (or 1.5, 2.5,
>> ... etc) than the reflected path - thus cancelling out the
>> signal waveforms.
>>
>> So you probably also know that two antennas set up the right
>> distance apart will help overcome this effect using the
>> default diversity switch mode, but if we use the above
>> technique to have two antennas with different gains, then we
>> run into EIRP limit troubles again.
>>
>> There *is* a solution! ;-)
>>
>> Once again, the Mikrotik systems come to the rescue with a
>> special 'Nstreme Dual' mode.  In this mode, a router with two
>> radios installed can be set up to transmit on one radio and
>> receive on the other.  The usual benefit of this technique is
>> to get a full duplex radio link, but the other cool benefit
>> is that we can also use dual high gain antennas on the
>> receive circuit for diversity, and one (or two) lower gain
>> antennas on the transmit.
>>
>> Sound cool?  I sure think so :-)
>>
>> So anyone interested in some experimentation?  I'm quite keen
>> to give it a go, and I'll even help you out by offering some
>> of this gear at or below cost.  If you're game, let me know -
>> on or off list is fine by me :)
>>
>> Cheers!
>>
>> _______________________________________________
>> Melbwireless mailing list
>> Melbwireless at wireless.org.au
>> http://wireless.org.au/mailman/listinfo/melbwireless
>>
>
>
>
> ------------------------------
>
> Message: 3
> Date: Fri, 31 Oct 2008 01:25:01 +1100
> From: Ben Balbo <ben at benbalbo.com>
> Subject: Re: [MLB-WIRELESS] Long distance links
> To: mike at viewbankrise.net.au
> Cc: melbwireless at wireless.org.au
> Message-ID: <4909C3BD.8040702 at benbalbo.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi!
>
>> Unfortunately I was defeated by trees (!) and my buddy there isn't willing
>> to set up a pole on his roof, so I'm back to square 1.
>
> Whereabouts in Portarlington? I have a place there and am hoping to get
> a friend on Langdon St, between Fisher and Brown, involved as he's
> higher up than I am. Alternatively, I'd be happy to whack a pole on our
> place (subject to council blah blah) on the corner of Batman and Willis.
>
> BB
>
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> End of Melbwireless Digest, Vol 37, Issue 12
> ********************************************
>