Multislot transmit power - possible to reduce it? (plain text)

Steve Harrison steveh7070 at gmail.com
Sun Nov 3 16:34:42 UTC 2013


Sorry, forgot to tick the "plain text mode" box on my previous mail...

Hi all,

In the "EMI" application's main.c is an interesting comment:

/* hack: because we cannot control power of multiple burst,
* we just force power to 1w, as it is fixed in dsp_extcode

If I understand this correctly, the 'C54 code in
src/target/firmware/calypso/dsp_extcode.c sets the transmit power to
maximum (1W) for all multi-slot transmissions.
Would it be possible to fix the multislot transmit power (for the TRX
app as well as EMI) at some lower value instead (e.g. 100mW) by
modifying dsp_extcode.c? Three reasons:
1. Play nicely with "other users" of the GSM band, by transmitting the
same as a "proper" picocell,
2. not draw such a high current from the phone's tiny battery, and
3. avoid overheating the phone's RF power amp and other circuitry - I
left my S-E J100 transmitting for about 5 minutes, then noticed that
the LCD display was starting to "white out" with the heat!

I've achieved a similar result by a hardware modification (added a
resistor to reduce the power-control voltage going into the PA), but
it's a brutal process - requires prying open a screening can and
soldering an 0402 resistor, then trying to get the screening can lid
to go back without too much deformation. A software mod would be much
more elegant, but I don't know C54 DSP code. Sylvain?

thanks,
Steve




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