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List:       neo1973-hardware
Subject:    Re: GSM-noise "buzz" issue / GPS coupling
From:       Joerg Reisenweber <joerg () openmoko ! org>
Date:       2008-09-19 17:14:30
Message-ID: 200809191914.37886.joerg () openmoko ! org
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Am Do  18. September 2008 schrieb Andy Green:
> There is definitely a story waiting to be uncovered here.  On my GTA02
> A5 "skelephone" that is just a PCB, I replaced plastic GSM antenna with
> "random piece of wire".  The buzz comes fine.  "Over the air"
> contamination does not involve antenna radiation pattern then, it is
> suspicious.  It means PCB inherently couples "something" "somewhere"
> before antenna.  I keep going back to power rail-borne contamination but
> it doesn't fit with beads doing something on headset nets.

Not "doing something" but actually stopping noise completely, according to Len 
and Candy.
We also heard noise is stopped by connecting external GSM-antenna, as well as 
by removing JK4401, and I managed to induce noise by "alien" RF fed to the 
phone (actually near hs-jack JK4401) by using some test-phone placed near to 
it.
Power-rail has been examined by me for a whole day more than 2 months ago: 
result negative.
So I don't exactly get it what's your conclusion from replacing 
plastic-GSM-ant by a "random piece of wire". Especially I don't know 
about "antenna radiation pattern" of this wire and how it should differ from 
the one of plastic-antenna. Actually probably nobody can tell exactly about 
the particular characteristics incl radiation pattern of any antenna setup, 
until you actually did decent research on a prototype. That's the main 
culprit for RF-design resembling black magic rather than logic-based EE.

/jOERG

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