Questions about power consumption


I began to be involved in using wavecom modem for some development. I am curious about a few questions regarding the power consumption and management.
The first one, is the power control method automatically implemented in the modem? that is, the modem automatically adjusts the transmission power within different comm. environments? any AT command to set the power control on/off?

The second, from the Spec of Wavecom modems, in Tx mode, the normal peak current is about 150mA, but I observe about 30mA in total in the device using the modem. The device acquires data once every 10 minutes and transmits data every 60 minutes. When not acquiring data or transmitting data, it is in sleeping mode. The device is powered by an external power supply which gives readings of the output voltage and current.

The third question is not about power consumption, but is still about the same modem. When the device transmits data, it first registers with the GSM network. If the registration fails, then the comm. can’t go ahead. How long is the registration session normally? what AT command calls the registration function?

Thanks for any information.


Which “modem” are you talking about?

The Fastrack modem has an integral switch-mode power supply - so the current depends upon the voltage!
I did some measurements on a Fastrack: … Traces.pdf

Normally the session lasts indefinitely



Thank you for your prompt reply.

Wavecom Q2406B. It is a bit old :cry:

Thanks for sharing your measurement. I don’t have a rig to test the modem separately; I don’t need either-I am more concerned the total power consumption. The external power supply gives 3.9V. This is very low compared what you used in your measurement (at least 5.5V), isn’t it? I don’t know if the internal circuit has converted the 3.9V to some higher voltage for the modem.

Maybe my measurement circuit can affect the power consumption? How did you put the oscilloscope into the measurement circuit? I add a 1-Ohm resistor between the power supply and the device, then measure the voltage across the resistor. This may reduce some current, but I think it should not be very significant.

I just find from another source that many modems set default timeout = 30 seconds. Can be changed. Don’t know if this applies to Q2406B.



That would generally be called a “module” - not a “modem”.

A “modem” implies a complete, packaged, standalone unit - like the Fastrack…

I used a MAX471 High-Side Current-Sense Amplifier:

With the large peaks required by GSM transmitters, I think 1-ohm is quite likely to have an adverse effect…

What source was that?
I’ve never heard of that!

I doubt it!


I am not familiar with the modem. I think you are right. It is card embedded in the device (data logger). Do you think the “module” can consume less power than the “modem”? I want to measure the power consumption in the whole device, which includes micro controller, ADC module, radio transmission module, etc.

:open_mouth: Does it? I have no clue. I will try your way…Thanks.

Look at: … _aug06.pdf - Similar pages
Page 12: 5.3.3 Extending the Default Time-Outs

Do you know power control in Fastrack? I mean, does Fastrack always transmits the same signal strength, or it adjusts the transmission strength according to the channel status?


Yes - for a start, the module has no RS232 transceiver. There will also be losses in the modem’s built-in Switching power supply…

I want to measure the power consumption in the whole device, which includes micro controller, ADC module, radio transmission module, etc.

Just think about Ohm’s law - a 1A current peak will cause a 1V drop in a 1-ohm resistor…

That document no longer seems to be available - it’s now … _feb08.pdf

You are misinterpreting what it says:
It is not talking about GSM registration - it is talking about the timeout for connecting a call before the modem gives up and says, “NO CARRIER”

If the unit were not GSM registered, it wouldn’t even attempt to dial - so the timeout wouldn’t apply. It’s just the same as if a landline modem gives “NO DIALTONE”.

I don’t know, but power control is a standard part of the GSM Specs - so I’d be surprised if it doesn’t…


Now the new document seems to have disappeared - what’s going on?!


Now it appears in the old place :slight_smile: don’t know what is going on ;(


Yes, it seems that power control is embedded in the GSM module. I did some experiments by using a metal cover to reduce the signal strength. I can see higher current consumption in the transmission device. Power control method adaptively adjusts the transmission power according to received signal strength at the base station (?), so that the QoS or SNR at the base station keeps about constant. This description is pretty general. I want to know the exact QoS level or SNR level that is expected to maintain at the basestation? what is the exact received signal level that is expected at the base station? All after all, I actually want to know exactly how much power should be consumed in my mobile unit in normal communication, and what is the normal current level.

Do you see what I mean? and any idea?

Thanks in advance.


Another question, how does the Wavecom modem adjust the transmission power level, by adjusting the current or adjusting the voltage? I don’t know the detailed circuit inside the modem.