joerg at openmoko.org
Tue Aug 5 18:16:59 CEST 2008
Am Di 5. August 2008 schrieb Andy Green:
> Somebody in the thread at some point said:
> |> So it comes and goes in discrete steps and it lags behind the change of
> |> position.
> | That's exactly the behaviour we would expect when noise is related to
> | MS-TXPower controlled by a PCL command from BS. BS isn't responding to
> | momentary change in signal-strength of inbound MS-signal, instead BS does
> Sounds good.
> Just a note, on the "skelephone" that I use I replaced the GSM antenna
> with a short length of patch wire, it still works (and some guy was
> complaining normal GTA02 is for hardcore hackers). I guess if I
> shortened it further, it can force base station to tell me to use max
> power all the time. RF performance seems fine with $WIRE like 5cm long.
When shorting the wire, we reduce antenna gain. This basically means we need
more power from battery, to have the same RF signal strength. So yes,
probably BS would level up the PCF, but only to the point where we have same
local RF field around GTA02. As noise is supposed to be introduced to GTA02
by own (and externally applied) RF, and not by battery current LF/DC, the
only effect would be a reduced battery life time.
In fact it's the SWR [http://en.wikipedia.org/wiki/Standing_wave_ratio] that
gets worse when creating a impedance missmatch by shortening antenna, so a
part of the RF-power is reflected at antenna rot point and fed back to
amplifier and dissipated producing heat. Depending on power and design of
last amplifier stage this can even burn out the amplifier.
Of course reducing the antenna gain is a little bit like flashing another
power class to the firmware, in that it limits the maximum effective RF power
the device can emit. So maybe this could be one of the possible fixes for
this issue (a very nasty one, that probably even won't yield the desired
results) to reduce gain by crippling the built-in antenna.
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