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Author Topic: what exactly *IS* CW... and how are there sidebands?  (Read 7298 times)
AK4YA
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Posts: 106




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« Reply #30 on: August 30, 2012, 03:13:32 PM »

Please knock it off guys.  Some of you are acting like a bunch of little girls.  I do appreciate the answers I am getting here, 1 last topic:

I have been assuming that each odd harmonic was a sideband, but after thinking about it and the Fourier summation for a square wave, that cannot be correct.  So tell me if this is correct:

1. The rise/fall shape determines how many harmonics are created
2. Each harmonic ends up 100% AM modulating the carrier to create 2 sidebands, 1 above and 1 below the carrier.

Are those 2 correct?

And, for some reason, at the minumum, the 5th harmonic is the lowest harmonic you want.  Im not sure why.  Im sure it has something to do with the squareness of the waveform but I cannot find any math for that.
« Last Edit: August 30, 2012, 03:25:26 PM by KC5VNN » Logged
PA0BLAH
Member

Posts: 0




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« Reply #31 on: August 30, 2012, 04:32:18 PM »

Please knock it off guys.  Some of you are acting like a bunch of little girls.  I do appreciate the answers I am getting here, 1 last topic:

I have been assuming that each odd harmonic was a sideband, but after thinking about it and the Fourier summation for a square wave, that cannot be correct.  So tell me if this is correct:

1. The rise/fall shape determines how many harmonics are created
Correct. The blockwave consist of a fundamental also mentioned first harmonic and higher harmonics. The first harmonic is somewhat larger then the block amplitude.  The n-th harmonic has amplitude 1/n. for n odd,

All those harmonics you find left AND right of the carrier as sidebands. Not every sideband is separately modulating the carrier 100% because they are smaller, However together they do that,
Quote
2. Each harmonic ends up 100% AM modulating the carrier to create 2 sidebands, 1 above and 1 below the carrier.

Are those 2 correct?
One harmonic , the  fifth, has amplitude somewhat more then 20% of the block amplitude, so the upper and lower sideband will be both 10% , and the modulation depth of that 5 th harmonic only 20%
Quote
And, for some reason, at the minumum, the 5th harmonic is the lowest harmonic you want.  Im not sure why.  Im sure it has something to do with the squareness of the waveform but I cannot find any math for that.

Draw on a piece of graph paper 3 sinewaves, sin x ,  0.33 sin 3x and   0.2 sin 5x ; for x 0 to 360  degree, add on each time the 3 momentary values and you get your block like signal with moderate slope. You can also calculate the sum and draw the result for every x.
« Last Edit: August 30, 2012, 05:00:12 PM by PA0BLAH » Logged
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