William Sommerwerck wrote:

"craigm" wrote in message
...
William Sommerwerck wrote:

As that time draws close, you'll have to turn the radio up a little
more to get the same volume, but you probably won't notice. Then, the
sound will become a little distorted, and you might eventually notice
that. Not too much later, what you describe will happen. (The FM
section takes more power than the AM and will stop working sooner.)

I've never seen a radio in which the tuner sections are separately
powered. Compared to the output stages, they draw little current.

Since the topic of this thread is the GE Superadio, you should look
at the schematics of the radio to provide some validity to your
statement. According to the schematics, both the Superadio I and
Superadio III remove power to the tuner circuits not being used.

My statement is completely valid -- I've never seen one.


You need to take a closer look at portable radios. Your limited experience
does not make for a valid generalization.


While the tune sections may draw little current relative to the audio
circuitry when performing at full output, at lower output, the extra
current can have a significant impact on battery life.

If they draw little current -- relative to the audio stages -- then they
cannot have a "significant" impact on battery life.

Note that I referred to _full_ output, at lower output the difference can be
significant.

For example, with the volume all the way down, the current draw an a
Superadio II is 15.7 mA for AM and 22.5 mA for FM. The FM front end draws
6.8 mA more than the AM one. At low volumes these numbers increase to
18-20 mA for AM and 25-29 mA for FM. Since FM seems to draw 7 mA more than
AM, listening to AM and leaving the FM powered up may increase consumption
by about 33%.

At higher volumes the current for AM is 38-50 mA and for FM is 48-70 mA.
At thee levels, the increase in current is a smaller percentage. (I'll let
you figure out the math.)

The above numbers are measured on a real radio, no conjecture. The ranges
are indicated because the program content caused variations in the
readings.



And very few radios -- the GE P970A being an exception -- have
separate AM and FM tuners. We never established if this was the
case with the Superradio.

However, if your definition of tuner includes all the circuitry from the
antenna to detected audio, the Superadio I and III do not have separate
tuners as they both have common IF circuits.

I asked about this several weeks ago, but no one responded.

If these radios have common IF strips, then what sections of the circuitry
are there to be shut off when not in use?

RF amps, mixer, oscillator, portions of the IF that are not common.



FM/AM radios commonly use the same transistors for the RF amplifier, the
mixer, and LO. Are these Superadios different?

Yes they are different. This question shows how little you know about what
you are talking about.

For more info on the SR III look here.
http://users.netonecom.net/~swordman...srIIIAlign.htm