Spurious Reports

Rx Spurious Report (available in a Receiver project only)

The Rx Spurious Report displays frequencies that create in-band interference components. Spurious frequencies are a result of non-simple mixers being present in your design. While there are no limitations on the number of non-simple mixers you may have in a design, the number of calculations necessary to cover all the spurious possibilities grows exponentially with the number of mixers.

Note — A printout of the report shows only a limited number of the spurs listed in the control; however, the full data in the report can be exported to the clipboard and then imported into another application such as Excel. To export the data, right mouse click on the spurious table and select 'Copy table to clipboard' from the menu. The clipboard contents can then be pasted in Excel or any other OLE application.

Column Definitions

Spur (MHz)	The spurious input frequency. This frequency (or some harmonic thereof) will propagate through the design and combine with an LO harmonic of each mixer encountered to produce a spurious in-band signal.
RF (MHz)	The frequency to which the system is currently tuned (see Source Palette) or the tuned frequency causing the worst case spur. This depends on whether Worst Case Frequencies is checked on not (see below). To determine the LO frequencies involved in the calculations, set the input to the frequency listed in this column using the Source Palette.
Level (dBm)	The absolute level of the spurious input necessary to produce the same level at the output as a desired input signal at MDS level.
Margin (dB)	The relative level of the spurious input above MDS. The relative level is a measure of the receiver's ability to discriminate between the minimum detectable input signal and an undesired signal at any other frequency to which it is responsive. This number is normally positive, but may be negative under certain conditions (see Margin Considerations)
Mixer1	The N X M harmonic of Mixer1 contributing to the spur. N and M are the RF and LO harmonics respectively.
Mixer2	The N X M harmonic of Mixer2 (if present) contributing to the spur. N and M are the RF and LO harmonics respectively.
MixerN	The harmonics used in the calculation of the Nth mixer.

Other Controls

Start	The spurious analysis is not automatically performed since it can be quite lengthy. To begin the analysis, you must click the Start button.
Worst Case Frequencies	Check this box to perform the analysis at the worst case tuned frequency. If unchecked, the analysis is performed at the current frequency specified in the Source Palette whether it results in the worst performance or not.
Include Mixer Suppression	When checked, the analysis includes the harmonic attenuation found in attached intermodulation data files (see Mixer Specifications). If unchecked, or if there are no attached IM data files, the analysis shows the system performance based on filters only. This can be helpful when assessing system performance in light of poor mixer performance.
Ignore Spurs	Allows you to set a threshold above MDS after which spurs are not reported.
Options	Invokes the Options dialog box shown below.

The report shown above is for a design that contains two mixers in the cascaded chain. As an example, the calculations necessary to produce the results in the first row would be performed as follows:

The receiver input is tuned to 824 MHz. Depending on the injection side and IF specification of the mixer(s) in the design, an LO frequency(ies) is implied. The actual LO frequencies used in the calculations are not referenced in the table but can easily be determined by manually tuning the input to the frequency listed in the Rx column using the Frequency palette. The LO frequencies involved are listed under each mixer.
The spurious input will propagate through the chain, experiencing gains and attenuations due to any components encountered, until it eventually arrives at the first mixer.
Based on the products listed in the Mixer1 column, the first harmonic of the LO (mixer1) would be subtracted from the first harmonic of the spurious frequency (914 MHz) to produce an interference IF in mixer1. The conversion gain experienced by the spurious signal will depend on whether or not an intermodulation data file (see Mixer Specifications) is attached to the mixer. If no file is attached, then the spur will convert using the same gain as the desired signal (specified in the Properties Dialog). If a file is attached, then the spur will convert using the loss specified for the specific RF/LO harmonic combination.
This new frequency and level then propagates through the remainder of the chain to eventually reach the second mixer. Based on the products listed in the Mixer2 column, the first harmonic of the spurious frequency would be subtracted from the first harmonic of the second mixer's LO to produce the final interference IF frequency exiting mixer2.
Eventually, the spurious level reaches the output. This level is compared to the level that would be present at the same point for a desired input signal at MDS level. The Spurious input level is then adjusted until the spurious output is identical to the desired output. This spurious input level is listed in the Level column of the report. The Margin column simply lists the difference between the Level column and the system's MDS level.
The calculations for any other row are likewise explained.

Margin Considerations

Under normal circumstances, the values indicated in the Margin column are positive numbers reflecting the difference between a spurious signal's level and the desired signal at MDS level. It is possible, however, for a negative value to appear in this column. If the filters in the system are misaligned or if the desired frequency is down the skirt of a filter, the desired signal may actually see more attenuation than a particular spur. For instance, when you select "Worst Case Frequencies" in the dialog above, the analysis is performed across the entire tunable frequency range. If the input signal is appreciably attenuated at the band edges as compared to mid-band, then the margin is degraded accordingly. An "unattenuated" spur, in this case, would actually have a lower required power level than the desired signal; hence, a negative number would be indicated.

Tx Spurious Report (available in a Transmitter project only)

The Tx Spurious Report displays frequencies and levels that are emitted from the system as a result of non-simple mixers being present in your design. While there are no limitations on the number of non-simple mixers you may have in a design, the number of calculations necessary to cover all the spurious possibilities grows exponentially with the number of mixers.

Column Definitions

Spur (MHz)	The spurious output frequency.
Po (dBm)	The absolute level of the spurious output frequency.
Margin (dBc)	The relative level of the spurious output above desired output level
Mixer1	The N X M harmonic of Mixer1 contributing to the spur. N and M are the RF and LO harmonics respectively.
Mixer2	The N X M harmonic of Mixer2 (if present) contributing to the spur. N and M are the RF and LO harmonics respectively.
MixerN	The harmonics used in the calculation of the Nth mixer.

Note In a transmitter design, the LO leakage (M=0) will radiate from the mixer into the output directly. If you have attached a Data File to a mixer, then the leakage from that mixer will be the declared LO injection level reduced by the harmonic attenuation indicated in the table. If you have specified Global Suppression settings for the mixer, the leakage will be the entered amount regardless of harmonic.

Other Controls

Start	The spurious analysis is not automatically performed since it can be quite lengthy. To begin the analysis, you must click the Start button.
Include Mixer Suppression	When checked, the analysis includes the harmonic attenuation found in attached intermodulation data files (see Mixer Specifications). If unchecked, or if there are no attached IM data files, the analysis shows the system performance based on filters only. This can be helpful when assessing system performance in light of poor mixer performance.
Include Spurs Greater than	Output spurs exceeding this level (dBm) are included in the report.
Include Spurs Less than	Output spurs less than the indicated attenuation (dBc) below the desired output are included in the report.
Options	Invokes the Options dialog box shown below.

Options Dialog

The options dialog allows you to specify limits applied to the analysis.

Harmonic Limits - The dialog below allows you to specify the range of cross products use in the spurious analysis. You can specify the starting and stopping harmonics for the RF and LO independently. The harmonic limits apply to all mixers.
RF(n) - Start	The lower harmonic limit used for the RF frequencies.
RF(n) - Stop	The upper harmonic limit used for the RF frequencies.
LO(m) - Start	The lower harmonic limit used for the LO frequencies.
LO(m) - Stop	The upper harmonic limit used for the RF and LO frequencies. Note — If you specify upper harmonic limits beyond the data supplied in an attached mixer, SysCalc will use the attenuation specified at N X N for that mixer (see Mixer Specifications and Mixer data files).
Single Spur Only	When check, the spurs for the indicated N X M harmonic will be evaluated.
Frequency Limits
Lower RF	Defines a lower limit below which input frequencies to the system are not considered during spurious analysis. The default value is zero.
Upper RF	Defines an upper limit above which input frequencies to the system are not considered during spurious analysis. The default value is zero.
Maximum Product Order	The maximum spur order (n + m) analyzed by SysCalc.
Maximum Spur Count	The maximum number of spurs appearing in the table.