Produce a spur graph for a multiband transmitter or receiver
Vertical green bands, representing spur-free zones.
Horizontal colored bands, representing spurious regions.
The following figure shows a spur graph for the three-mixer multiband receiver example on the OpenIF class reference page.
Spur-free zones are ranges of possible IF center frequencies that are free from intermodulation distortion. Depending on the configuration of the mixers in hif, spur-free zones may not appear. Clicking on a spur-free zone produces a tooltip, which displays information about the spur-free zone:
Min IFCF — The minimum possible IF center frequency fIF for the corresponding spur-free zone.
Max IFCF — The maximum possible IF center frequency fIF for the corresponding spur-free zone.
Spurious regions contain intermodulation products from at least one mixer. The color of a spur on the spur graph indicates which mixer generates the spur, according to the legend on the spur graph. Clicking on a spurious region produces a tooltip, which displays information about the spur:
RF Center Freq — the RF center frequency fRF of the mixer that generates the spur
M, N — the coefficients in the equation |MfRF – N(fRF ± fIF)| (down-conversion) or the equation |MfIF + N(fRF ± fIF)|. The sign of ‘±' in these equations is determined by the injection type of the mixer. These coefficients refer to the particular mixing product that generates the spurious region.
Spur Level — The difference in magnitude between a signal at 0 dBc and the spur. If you set hif.SpurLevel to a number greater than this value, then hif does not report the region as spurious.
Freq Range — The frequency range of the spurious region. Choosing an IF center frequency in this range causes interference with the intermodulation product corresponding to the spur.
The getSpurFreeZoneData returns the endpoints of the spur-free zones in a matrix.
The report method displays mixer configurations, intermodulation tables, and spur-free zone information at the command line.
The OpenIF class reference page contains an example that shows how to find the spur-free zones of a multiband receiver with three mixers.