This is interesting as it shows the detector being frequency selective, but having zero/no rejection of external signal. Which is the opposite of the example in the first post (external signal rejected). Do you know why this is so different? What options/methods/parameters can a user control to make such a difference?
Unless I missed something, in the OP the spurious tone is simply added to the input. Its frequency is also conveniently located on a sweep point, where it will basically just increase stimulus power and maybe shift the phase (both of which is accounted for through the reference channel). And the step size is probably larger than the receiver BW, so adjacent points are hardly affected.
We had some time and repeated some tests using a "spurious tone" at 10KHz with a linear sweep of 500 points from 5KHz to 15KHz . Setup was 2 separate AWGs and DSO set to 10X probes and 20MHz BW. AWG spurious tone set to 10VPP and Stimulus AWG set at 1VPP. A second DSO was used to monitor the Input and Output waveforms.
First plot shows result with CH1 driven by AWG Stimulus and CH2 driven by Spurious AWG, no connection between CH1 and CH2. The Bode result appears to have a response to the Spurious Tone with a BW of ~ 1KHz.
2nd plot shows CH1 and CH2 now connected by a 1K Resistor. Edit: See 7th for better plot!
3rd shows CH1 disconnected (no Input signal).
4th shows both AWG summed together with 100 ohm resistors and connected to CH1, CH2 and CH1 still connected by 1K Resistor.
5th shows same as 4th but Spurious AWG frequency changed to 10.063KHz & 100 points Bode sweep.
6th shows same as 2nd (CH1 and 2 connected by 1K, Stimulus AWG to CH1, Spurious AWG to CH2) but with Spurious AWG frequency 10.063KHz & 100 point sweep.
Edit: 7th added for better display of 2nd plot!!
This seems to show that the Spurious signal when applied to the Input (CH1) along with the Stimulus doesn't affect the plots, and with the Spurious applied to the output (CH2) does affect the resulting plots. Changing the Spurious frequency to not land on one of the Stimulus points seems to have no effect.
No attempts were made to keep the signals "clean" nor shielded, just a quick clip lead setup with leaded resistors.
Best,