3G Radio Always on When Screen On? According to JuicePlotter, my HTC Evo's 3G radio is always on when the screen is on -- even when doing absolutely nothing.  I tested this by turning the brightness down to 1 and opening the settings menu and just leaving it there.  The screen was set to never shut off.  I got pretty significant battery drain.

I ask because I want to improve my battery life when reading downloaded books with the Kindle app.  It seems to me that the radio should be in sleep mode when not in use.  I'd rather not switch to airplane mode because I'd still like to receive calls/texts.

To clarify:


I have a strong signal at all times
When the screen is off, JuicePlotter says the radio is off (and the battery lasts practically forever)
When in airplane mode with the screen on, JuicePlotter says the radio is off (duh) and the battery life is much better.
Android reports that my display only consumes between 5 and 10% of power
Android reports that Cell Standby consumes 30% (and that's with great signal)


I think these tests demonstrate that the display itself is not the problem, the radio is.  So again the question is:  why does the radio use so much power when the screen is on but it's not being used?
With cdma phones the data and voice use the same radio. Its going to run all the time anyway because its constantly syncing data, towers, location... If you want to stop it without turning off voice you should turn off the apn. Doing this will not put your radio to sleep but it will reduce your power consumption.  Check into apndroid or quick settings, and tasker to set triggers and automation.