Peter

I quote your message:

"Amplitude Modulation... The output level "swings" above
and below the carrier level."

This is incorrect. The output does not swing above and below the
carrier. The output of an AM signal is the carrier and the two
sidebands.

Also power meters are not, per se, frequency specific. There are
tricks that allow psuedo peak reading to see the "swing" that comes
with modulation. Usually this is done by using larger value capacitors
in rectified output of the RF detectors. The problem is all RF is
rectified to a time varying DC level that corresponds somewhat to the
varying amplitudes of the RF signals being sampled.

james


On Tue, 4 Sep 2007 05:53:47 +0100, " Peter"
wrote:

|
|"james" wrote...
| " Peter" wrote:
|
| |Amplitude Modulation... The output level "swings" above
| |and below the carrier level.
| |
| |Get it yet?
| |
| |If the output level does not swing, then you have a constant
| |amplitude... no amplitude modulation.
| |No amplitude modulation = no audio. Unless, of course,
| |you are using FM.
| |----------------
|
| Wrong
|
|Once again you appear to have misread my statement,
|making it appear that we disagree.
|
|Before going on, read the quote (above) and note that:
| I said output... NOT carrier.
| I did NOT say that average power changes.
|
| Unless you are using a peak reading wattmeter the power
| remians constant
|
|The power is not affected by the type of meter, all that
|changes is the type reading that you take.
|
| with modulation in a DSB-AM Large Carrier signal. IF you were
| to do a Fourier Transform of the AM signal under modulatioin
| you will see a carrier frequency, the upper sideband frequencies,
| and the lower sideband frequencies.
|
|There is no dispute that extra power is now in the sidebands,
|but the output is varying over time, as an oscilloscope would
|show.
|The total power is varying with the modulating signal but,
|as it should be swinging about the carrier level, the
|average should be constant.
|
|Surely we agree: the peak output (not carrier or average)
|is varying over time, while the average power is constant.
|At least is should be, if all is well and nobody has been
|fekkin about inside the radio.
|
| With an averaging wattmeter you should see little
| or no movement of the power.
|
|Of course not, the meter is intentionally ignoring them.
|By averaging the reading, you are removing the short term
|variations... but that does not mean they are not there.
|
|Just like a business looking at average sales - the seasonal
|fluctuations are ignored, but they still exist.
|
|
|Hey, how about a new CB voodoo term...
| Seasonally Adjusted Power.
|No? How about:
| Seasonally Adjusted Bird Watts.
|
|Come on, James... laughter may just save you from being
|sent suicidal by this group.
|
|
|Regards,
|Peter.
|
|