杂散表的阅读

杂散表得阅读 —— 以Marki公司得手册为例

混频杂散（Mixing Spurs）是指信号经过混频器时，不仅会与本振混频，还会与本振的高次谐波混频（对于第二章说的方波本振，信号只与本振的奇次谐波混频因为方波只含有奇次谐波）。因此存在干扰信号与本振的高次谐波混频产生的混频杂散刚好落在中频区域的可能。（所以在接收机中，不是下变频次数越多越好，就是因为混频杂散问题）

Spur Table

Downconversion Spurious Suppression

Downconversion Spurious Suppression Spurious data is taken by selecting RF and LO frequencies (+mLO+nRF) within the 10 MHz to 20 GHz RF/LO bands, which create a 100 MHz IF spurious output. The mixer is swept across the full spurious band and the mean is calculated. The numbers shown in the table below are for a -10 dBm RF input. Spurious suppression is scaled for different RF power levels by (n-1), where “n” is the RF spur order. For example, the 2RFx2LO spur is 61 dBc for a -10 dBm input, so a -20 dBm RF input creates a spur that is (2-1) x (-10 dB) dB lower, or 71 dBc.

A sample downconversion spurious sweep is shown below. An LO which is 100 MHz higher than the RF is used to create a 100 MHz reference IF. A second LO is used to create a 2x2 spurious IF, also at 100 MHz (50 MHz fundamental IF). The difference between these two output levels is the spurious suppression in dBc. The mean value across the full 10 MHz to 20 GHz RF input band is the number shown in the table above.

杂散表区分上变频和下变频2个表。

这个表以-10dBm功率的RF输入下，讨论各杂散与IF信号的功率差（dBc）

直接写的表示是方波作为LO的杂散，括号里的表示正弦波作为LO的杂散。比如以2×RF与2×LO的位置，即RF与LO的二次谐波混频后得到的杂波的均值，以正弦波作为本振输入时，中频信号与该杂散信号的比值是57dBc，以方波作为本振输入时是61dBc。

杂散表里数据的产生：在带宽（这里是10MHz-20GHz）中调整RF和LO信号以产生100MHz的IF信号。比如设置RF为10MHz时，为了保证100MHz的IF输出，所以设置LO的频率为110MHz。于是，RF从10MHz测试到20GHz时，对应的LO需要从110MHz设置到20.1Ghz。最后得到的值是整个带宽测试完之后，杂散值得平均值。