A mixer datasheet quotes conversion loss and isolation; the spur chart tells you whether the receiver will see junk in the IF. Here is a compact way to read and use that chart before you freeze LO and IF plans.

1. The naming
An m×n spur is the product |m*f_RF ± n*f_LO| (or the opposite assignment depending on vendor). Order is |m|+|n|. The desired downconversion is usually 1×1: f_IF = |f_RF - f_LO|. Images, half-IF and harmonic mixes are the rest.

2. Classic traps
- Image: f_LO + f_IF (high-side LO) or f_LO - f_IF (low-side). Same conversion loss as the desired path unless the front end filters it.
- Half-IF: a tone at f_LO ± f_IF/2 mixes via 2×2 into the IF. Dangerous in wideband tuners with weak RF filtering.
- LO second harmonic: 2*f_LO - f_RF can land in IF when RF sits near 2*f_LO - f_IF. Common when LO range is wide.
- IF feedthrough and LO leakage: not mixing products, but they steal spur budget and desensitize later stages.

3. Reading a spur chart
Vendors plot spur level in dBc relative to the desired IF for a stated RF drive (often -10 dBm) and LO drive. Example reading:
- 1×1 desired at 0 dBc reference
- 2×2 at -50 dBc, 3×3 at -60 dBc: good for many narrowband IF plans
- 1×2 or 2×1 at -40 dBc: check whether that frequency can be occupied by a blocker in your band plan

Always renormalize to your actual RF level. Spurs often improve faster than 1:1 as RF drive drops, but LO-related leakage may not.

4. Worked frequency-plan check
Want RF 2400 to 2480 MHz, IF 70 MHz, high-side LO 2470 to 2550 MHz.
- Image band: 2540 to 2620 MHz. Put a preselect that is already down by >40 dB there.
- Half-IF zone: around LO ± 35 MHz, i.e. overlapping the RF band itself. Prefer a mixer with strong 2×2 rejection or tighten RF filtering.
- 2*LO - RF: LO=2500, RF=2430 → 2570 MHz product abs value path into IF depends on the internal routing; verify on the chart for 2×1 / 1×2.

5. Mitigation order
1) Choose IF and LO side so the worst chart spurs fall outside the preselect.
2) Raise LO drive only as far as the chart shows diminishing returns (overdriving can worsen some spurs).
3) Add RF filtering before the mixer for image and half-IF; add IF filtering after for LO leakage.
4) Balanced / double-balanced / IQ topologies improve even-order and LO-RF isolation; they do not erase a bad frequency plan.

6. Bench confirmation
Inject a swept CW blocker at the predicted spur frequencies while a desired tone is present; measure IF SNR change. If the chart said -55 dBc and you see -40, look for cable leakage, insufficient LO drive or a saturated LNA ahead of the mixer.

Freeze the spur sheet next to the frequency plan. If they disagree, change the plan, not the plot scale.