#phase modulation

[tymkrs]

19.Phase Ham lesson o' de day

Phase Modulation:

Phase modulation is the encoding of information into a carrier wave by variation of its phase angle in direct proportion to an input signal.  So the greater that the signal is at a point in time, the greater the phase shift of the modulated signal at that point.  It can also be viewed as a change of the frequency of the carrier signal, and thus be considered a special case of FM.  And most of the time it is clumped in with frequency modulation.

From what I've been reading, phase modulation is solely for digital working.  Circuit below!

The modulating signal varies the capacitance of the diode, which then changes the phase shift of the carrier input and thus changes the phase of the output signal. Short and simple!

@atdiy/@tymkrs

http://www.knowledgerush.com/kr/encyclopedia/Phase_modulation/

http://www.neazoi.com/technology/varactordiodes.htm

[tymkrs]

Third Ham lesson o' de day

So we'll go back to this nifty diagram and talk a little about frequency modulation (FM).  In terms of basic shape, you see that as the signal goes up in amplitude (becomes more positive), the frequency of the resulting FM wave increases (more squiggles in a shorter amount of space).  And in turn, as the signal goes down in amplitude, the frequency of the resulting FM wave decreases (fewer squiggles in the amount of space).  This is frequency modulation. 

The amount of variation is called deviation or carrier deviation.  And an example of increasing deviation is speaking louder into the microphone of a FM transmitter.  If you increase the amplitude of your voice via volume, the frequency will increase in the modulated FM wave.

According to the Manual, if you increase deviation, you may also increase the bandwidth.  This I'll have to investigate because doesn't bandwidth increase/decrease based on the difference of the sidebands as shown in AM waves?

Anyway, there is also Phase Modulation.  This is just when a signal's phase (position) changes instead of its frequency:

So assume the first curve is the carrier, the second is the modulating signal (morse code or something) and you're dealing with phase modulation.  You end up with number 3!  Where you see that when the modulating signal changes, there is, instead of a frequency or amplitude change, a phase change!  The wave's position is completely topsy turvy!

It's good to note that both FM/PM are usually processed by the same circuitry.  And that because the amplitude of the FM signal doesn't change, unlike the AM waves, it'll have the same power modulated or not.

@atdiy/@tymkrs