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This frequency conversion calculator takes the input frequency band and converts it to output upper and lower sidebands.
If frequency (spectral) inversion occurs, a message is place above the Lower Sideband area.
If frequency folding occurs, a message is placed next to the LSB "Lower" frequency area.
Numerical inputs are not error trapped, but some warning messages
are provided. You can ignore them at your own peril.
Calculated values do not change until the "Calculate" button is clicked.
Please click this link for an explanation of Frequency (Spectral)
Inversion.
To the right is an illustration of Frequency Folding within the output band. Frequency folding occurs when the local
oscillator lies within the input band. Note how the Input Band frequency block has a graded fill pattern, with the lower
frequencies being darker and higher frequencies being lighter.
Notice what your get when you begin calculating the mixer difference frequencies (I will use increments of 10, and units
do not matter):
|
100 |
120 |
20 |
|
110 |
120 |
10 |
|
120 |
120 |
0 |
|
130 |
120 |
10 |
|
140 |
120 |
20 |
|
150 |
120 |
30 |
|
160 |
120 |
40 |
|
170 |
120 |
50 |
|
180 |
120 |
60 |
|
190 |
120 |
70 |
|
200 |
120 |
80 |
From 100 through 120, the output frequencies decrease as the input frequency increases (inversion), but from 120 through
200, the output frequencies increase as well (no inversion). This phenomenon is termed "frequency folding."
Of course this is an undesirable condition because from 100 to 140 there are two different frequencies that generate
the same output frequency. Where this scheme might be allowable is when the input band is broken in to a series of smaller
sections (using bandpass filters), along with a fixed LO.
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