Can passive repeater concept work for GSM mobile phones?

Faulks, Jason Jason.Faulks at det.nsw.edu.au
Mon Sep 6 06:01:11 GMT 2004


Chris + group,

It was with great interest that I read your original note about the
existing link in Karratha, and I'm keen to hear more detail from you or
anyone in the group for that matter on the subject of passive repeaters.
Your original note mentioned 3km for one leg of the link - what about
the other? Do you know anything about the power required to make this
work? What about the carrier freq?

I want to hook up (bridge a LAN) with a friend who lives down the valley
and across a bit, so to speak. It may be 5 or 6 km as the crow flies,
and probably not much more via a repeated signal path, which is
necessary because of this damned inconvenient bulge in the side of the
hill. Thus far, I have been put off by the cost of building an active
repeater (solar) and my previous research on the subject of passive
repeaters has been fairly disappointing in terms of what can be
expected. 

Are there any more specific details anyone can provide? I'm especially
keen to talk to anyone that has set up a fairly long range repeated
link. For that matter, I'd love to see the specs for an active rig that
someone on the group has built on a budget.

Regards, Jason

-----Original Message-----
From: Chris Young [mailto:cfcyoung at netscape.net] 
Sent: Friday, 3 September 2004 2:27 PM
To: chris.hill at crhtelnet.com.au; wireless at lists.samba.org
Subject: Can passive repeater concept work for GSM mobile phones?

Hi,
Was searching for info, came across the below (old) mail trail.
I'm very interested in this, as my house seems to be in a mobile 
(Telstra) black spot.  This in spite of 'towers' being reasonably
nearby.
So I can only speculate it's trees, terrain, maybe even beams & walls.  
Hence the "earth flattener" vs "range extender" comment is relevant.

Can such a concept work for phones - ie roof antenna, cable down into 
smaller antenna inside house?  I heard active / amplifiers break the 
law, so passive should be ok. 

I can understand if reception is improved.  But what about transmission,

ie 'talk'.  Does it work reverse - will signal from phone find the 
antenna outside, as the path of least resistance?  Otherwise it will be 
listen-good but talk-bad.

Thanks
Chris Y.

>Hi Tony, Robert and group,
>
>Actually, Robert it right about the inverse square rule.
>
>However, "passive repeaters" do work (subject to the laws of physics).
They
>can be thought of as "earth flatteners", rather than "range extenders".
>Their best application is in cases when you can summarise the link as:
"We
>would have HEAPS of signal on this link path, if only that great big
>building | hill wasn't in the way".
>
>The best example of a passive repeater that I've seen, is on a
ridgeline
>above the town of Karratha, in the Pilbara region of WA.  Two grid pack
>dishes are mounted back to back, interconnected only by a section of
>waveguide.  No electronics on site, no solar panels, no 240V.
>
>Down in the town (on the coastal plain), there's a microwave dish at
the
>exchange, pointing at the passive repeater.   Over on the other side of
the
>ridgeline, at a distance of about 3km (from memory) is the other end of
the
>link, to service the Light Industrial Area.
>
>To get over the ridgeline would have required ridiculously tall towers
at
>each end of the link.
>
>Unfortunately, I don't have any performance figures for this
configuration.
>
>I have also used the passive principle to provide multi-channel VHF
radio
>coverage underground over a leaky feeder system, where there was heaps
of
>signal outside, and none in the underground structure.
>
>As a guide, the passive systems work best when placed as close as
possible
>to one end of the circuit.  The middle of the link path is the
worst-case
>scenario (that inverse square rule again!).
>
>Hope this helps,
>
>
>
>Chris vk6kch
>


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