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  Frequency Conversion Calculator
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.

  Upper: RF Cafe - Input, Mixer, Output, LO
    Input Center: Center:
  Lower: Lower:

Please click this link for an explanation of Frequency (Spectral) Inversion.

Frequency Folding

RF Cafe - Frequency folding
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):

Input LO Output
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.

Related Pages on RF Cafe
- Spectral (Frequency) Inversion
- RF System Cascade Budget Calculation
- Example of System Cascade
- Frequency Modulation
- Frequency Modulation Fundamentals
- Mixer & Frequency Discriminators EW&RH
- Mixer Image Frequency
- Frequency Conversion Calculator
- A Graphical Approach to Mixer Spurious Analysis
- Mixer, Converter, Modulator & Transceiver Design
- Frequency Mixer, Converter, Multiplier, Modulator Vendors

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Webmaster:  Kirt Blattenberger, BSEE - KB3UON
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