The spurious emissions mode (SEM) is picking up spurs exactly 100 KHz away from the carrier frequency, when in fact there are no spurs to be found.
I'm using the N9030b PXA to measure spurious emissions.
Let me set up an example to describe my problem.
Let's say the carrier frequency is 15GHz at 0dBm and my SEM has the following 4 ranges greater than the carrier.
Range Start Stop Span RBW
1 15,000,000,050 15,000,000,100 50 Hz 1Hz
2 15,000,000,100 15,000,001,000 990 Hz 10Hz
3 15,000,001,000 15,000,100,000 990 KHz 100Hz
4 15,000,100,000 15,001,000,000 9.9 MHz 1KHz
For some unknown reason the SEM is finding a spur in range 4, at exactly 15.0001GHz (+100KHz from the carrier) with a power level that will be ~ -1dBm. When going into spectrum analyzer mode and checking that frequency there is no spur.
The strange thing is, if there was a spur at +100KHz then range 3 should have also caught the spur. Correct? Also, the power level on the "spur" is so high it seems like the analyzer is mistaking the carrier for the "spur".
I have tried reducing both the RBW and VBW to as low as 50 Hz with no luck.
Has anyone seen this before? Does anyone know what I'm seeing? I'm not very familiar with this mode and I assume I'm just missing some setting that needs to be turned on or off.
Thanks in advance.