Can passive repeater concept work for GSM mobile phones?

[Chris Young]

Thanks Steve, for a detailed reply.  Even a non-tech like me can 
understand that :-)

I will try it - it's relatively low cost.

Last resort - can always modify the rig below, to fit a "car kit".  I've 
read elsewhere that even without an external cable connector - and Treo 
600 doesn't have one - but the kit itself connects externally, and the 
cradle being close proximity to internal antenna, conducts or transmits 
better.  The disadvantage is - it will be model-specific, and one person 
use only. 

Rgds
Chris


sjenkin at canb.auug.org.au wrote:

>On Fri, 2004-09-03 at 14:27, Chris Young wrote:
>  
>
>>Hi,
>>    
>>
><snip>
>
>  
>
>>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. 
>>    
>>
>
>Unlikely you'll get what you want, BUT 'RF' is a tricky thing :-)
>Will cost you <$100 to rig up a temporary test. [High-gain outside
>aerial, co-ax, omni-directional internal aerial.  Don't know how you
>impedance match to limit SWR losses (Standing Wave Reflection?)]
>(Someone like Carl Makin would know)
>
>Amplifiers, per se, are not illegal - just look at all the mast-head
>amps on TV antennas in fringe areas.  They receive, not transmit...
>[The same people that do this work would be worth a call, it could be a
>'solved problem']
>
>  
>
>>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.
>>    
>>
>
>Reception will probably be fine: you've got a fixed transmitter and can
>point a high-gain antenna at it, then pipe this power down to an inside
>aerial.  I've heard of a guy in a difficult country location (in a
>mountain valley) who used two high-gain antennas back-to-back to get TV
>reception
>
>Like you anticipate, transmitting back to the base station could be
>problematic - you're transmitting from a omni-directional aerial to
>another low-gain antenna & piping the power (that's min 3db loss there)
>up to the high-gain directional antenna... That first link is very very
>lossy.  Standing close to the inside aerial may just work well enough
>for you - again, easy to test with a cheap testbed.  GSM phone output
>_is_ high: 5 watt max, and that could be enough to get you connection.
>[Having to go 'high power' will reduce talk-time battery endurance
>considerably]
>
>GSM works @ 900Mhz, well above VHF (TV) frequencies.  It is more
>'straight-line' than TV (and less than the 2.4Ghz & 5Ghz of 802.11a&b). 
>BUT, at these high-frequencies and modulation styles, signal strengths
>in the micro-watt range (-30dbm?) are all that's needed. (anyone know
>the numbers for sure?)
>
>A couple more comments in-line below...
>
>Hell, if things are really bad and there's a few of you down this
>particular hole, you could get your own 'micro-base-station' [not sure
>the correct name].
>Not sure how you get Telstra/Optus to put one in, or if you'd be
>expected to contribute some. [Remember Senator Alston got one :-) ]
>
>A second-removed family member of mine has done installs of these things
>all over Sydney.  Probably $50-100k to install. (Anyone know for sure??)
>
>HTH
>sj
>
>  
>
>>Thanks
>>Chris Y.
>>
>>    
>>
>>>Hi Tony, Robert and group,
>>>      
>>>
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><snip>
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>>>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.
>>>      
>>>
>
>Telecom/Telstra use this arrangement often.  It relies on:
>
>- Beams & very high-gain aerials for point-to-point, not
>broadcast/mobile comms.
>- Symmetry of stations: Both use directional aerials & identical xmit
>power
>- Collimated transmit beam (the spot is not much larger than the
>receiving dish at these close ranges & won't wander much with
>atmospherics)
>- modest power amplifiers (and they can increase power if they need)
>- High frequencies, low interference
>
>
>  
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>>>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.
>>>      
>>>
>
>This is what they do in road tunnels in Sydney for AM/FM radio _and_
>mobile phones...  In great company :-)
>I'm not sure if they've done it in train tunnels around the CBD there as
>well.
>
>And note the 'leaky co-ax' method works with mobile phone base-stations.
>As usual, the trouble is getting that base station connected back into
>the trunk network...  That's a landline or microwave link, which you'd
>use in preference to the mobile phone if you had the choice...
>
>
><snip>
>  
>
>>>Hope this helps,
>>>Chris vk6kch
>>>
>>>      
>>>
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