Mixer Spur Table Calculator
Generate every spurious product a real mixer can produce — m×fRF ± n×fLO up to order 11. Spurs are colour-coded by severity with named types, a live spectrum canvas, and CSV export.
| (m,n) | Order | Formula | f_spur (MHz) | Dist from IF | Status | Type |
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About the Mixer Spur Table Calculator
A real mixer is not an ideal multiplier — it is implemented with nonlinear devices (diodes, transistors, switches) that generate an infinite series of harmonic and intermodulation products. Every product has the form |m × f_RF ± n × f_LO| where m and n are non-negative integers. This calculator generates the complete table of these products up to the selected maximum order, classifies each one, and highlights any that fall within your IF passband.
The Universal Spur Formula
Spur order = m + n · Wanted IF: m=1, n=1, sign giving |f_RF − f_LO| = f_IF
Number of products up to order N ≈ N² (grows rapidly — order 7 gives ~50 products)
Named Spur Types
Image frequency (m=1,n=1, wrong sign): The mirror image of the wanted product — the second frequency that also downconverts to f_IF. Separation from f_RF = 2×f_IF. Cannot be removed post-mixer — must be rejected by a preselector filter before the mixer.
Half-IF spur (m=2,n=2): An interferer at f_LO + f_IF/2 generates a 4th-order product at f_IF. This spur cannot be moved by changing f_IF — it always sits f_IF/2 above the LO. Suppressed by double-balanced topologies and high IIP2.
IM3 products (order 3): Two RF tones create third-order intermodulation at 2f_A−f_B. These fall within the IF passband and cannot be filtered. Suppressed by higher IIP3 and reducing LNA gain.
LO harmonic spurs (m=1, n≥2): Higher harmonics of the LO mix with f_RF to produce outputs at |f_RF − n·f_LO|. Even LO harmonics (n=2,4) are cancelled in double-balanced mixers. Odd harmonics (n=3,5) survive.
LO feedthrough (m=0,n=1): The LO signal itself leaks to the IF port. Suppressed by port isolation — typically 30–50 dB in a double-balanced mixer.
Why the R⁴ of Mixer Design
Just as radar range depends on R⁴ making every dB precious, mixer spurious performance degrades rapidly with signal level. A 1 dB increase in input power raises the fundamental by 1 dB but raises 3rd-order products by 3 dB and 5th-order products by 5 dB. This is why large blockers — signals much stronger than the wanted channel — cause severe spurious problems even when the wanted signal is well within the linear range.