Mixer Spur Chart
A real mixer converts an input to the IF whenever |m·LO ± n·fin| = IF — not just for the wanted (1×1) response. This tool lists every spurious-response input frequency up to a chosen order, so you can see which incoming signals will break through to the IF. It flags the wanted response, the image, and the troublesome half-IF (2×2) response, and — given an RF preselector bandwidth — highlights the spurs your front-end filter cannot reject.
Equations & Parameters ▸
\(\lvert m\,f_{LO}\pm n\,f_{in}\rvert = f_{IF}\ \Rightarrow\ f_{in}=\dfrac{m\,f_{LO}\pm f_{IF}}{n},\quad \text{order}=m+n\)
\(f_{IF}=\lvert f_{LO}-f_{RF}\rvert \qquad f_{image}=f_{LO}+f_{IF} \qquad f_{\frac12 IF}=f_{LO}\pm\tfrac{f_{IF}}{2}\)
Critical when \(\lvert f_{in}-f_{RF}\rvert\le \tfrac{BW}{2}\) (inside the preselector).
\(f_{IF}=\lvert f_{LO}-f_{RF}\rvert \qquad f_{image}=f_{LO}+f_{IF} \qquad f_{\frac12 IF}=f_{LO}\pm\tfrac{f_{IF}}{2}\)
Critical when \(\lvert f_{in}-f_{RF}\rvert\le \tfrac{BW}{2}\) (inside the preselector).
| fRF | Input RF frequency (MHz). |
| fLO | Local-oscillator frequency (MHz). High-side (fLO > fRF) or low-side both work. |
| BW | RF preselector passband width (MHz), optional. Spurs whose input falls within fRF ± BW/2 are flagged as critical. |
| Max order | Largest m + n to search (2–9). Higher orders are progressively weaker. |
| Image | The mirror RF (2fLO − fRF) that also converts to the IF; reject it with RF filtering before the mixer. |
Reference: S. A. Maas, Microwave Mixers, 2nd ed., Artech House, 1993. · Standard superheterodyne frequency-planning practice.
Inputs
MHz
Wanted inputMHz
InjectionMHz
IF passband2 – 9
Results
Conversion
IF (|LO − RF|)—
Image frequency—
Half-IF response (input)—
Spurious responses—
Diagram