Jan

I don't have to go through your exercises, I am very well familiar
with diode ring demodulators and various other techniques to
demodulate audio in amplitude modualted sysytems. I am well aware of
the trade offs in effectiveness and costs of may different aprroaches.

james
On Tue, 13 Jun 2006 10:15:08 GMT, Jan Panteltje
wrote:

+++On a sunny day (Tue, 13 Jun 2006 00:32:38 GMT) it happened james
wrote in :
+++
+++A product Detector is prefered due to its mixer characteristics. Being
+++balanced, the two inputs are supressed sufficiently to make filtering
+++their components in the output much easier. Product detectors and
+++Envelope dection is not the only means of detecting DSB-SC and DSB-LC
+++signals. They are the most simplest and easiest to implement.
+++
+++I have used sampling to demodulate QAM, In any color TV you will find it,
+++carrier is regenerated in phase from the color burst, look up NTSC.
+++And there we have 2 modulating systems, here is how that works in the
+++time domain:
+++ http://groups.google.com/group/sci.e...ce23fcbb253646
+++
+++The main thing is perhaps that you can see that in SSB, if we have 1MHz
+++carrier, and 1kHz sine modulation, we get a 1.001 MHz carrier (or 0.999 if
+++the other sideband is used.
+++So to get the original back, it would be sufficient to substract the 1MHz
+++again in the first case (1.001 - 1) = 1kHz, or in the other case 1 - .999.
+++
+++In the DSB-SC case we would have 1.001 AND .999 AT THE SAME TIME.
+++
+++Using one sideband is enough. DSB uses double the bandwidth and as such
+++is less efficient then SSB,
+++
+++Distortion of the RF waveform may not nescessarily indicate that the
+++detected audio is unintelligable. As long as the recovered audio is
+++reproduced accuarately during demodulation then there is no
+++distortion.
+++
+++But it won't [work].
+++What the 4 diode ring modulator does, is make a RF amplitude phase phi
+++when the audio signal goes positive proportional to the audio amplitude,
+++and the same with phase phi+180 degrees when the audio signal goes negative.
+++If you do AM envelope detector (as the you normally do with a diode and RC
+++lowpass) you get a wave form that is no longer a sine, but looks like double
+++phase rectified sine when filtered.
+++
+++
+++ Spectral content of the demodualted signal can be set by
+++post detection filtering. This can reduce to some extent the harmonics
+++of the modulating signal.
+++
+++
+++
+++By the way the lab you point to is more about the generation of a DSB
+++signal. From figure 4 you are making statements about demodulation.
+++
+++Of course, lok at that waveform, build a 'non distorting AM detector
+++for it without carrier re-insertion (BFO, some oscillator), you CANNOT.
+++Modulation /demodulation is related.
+++
+++Please build one, try it,
+++
+++Since the information in both sidebands are indentical the only need
+++for the second sideband is to increase demodulated audio.
+++
+++Yes, we agree here.
+++
+++Please try it:
+++
+++But for the non-believers, try it out, all you need is an audio amp,
+++oscillator, 4 diodes, and of course a 27 HHz xtal oscillator.
+++http://www.nzart.org.nz/nzart/examin...les/Mixers.htm
+++There is a description and diagram a bit down on the page.
+++
+++Listen to it on an AM receiver, and you will KNOW.
+++