need guidance and help with signal modulation

[thundrous]

Hi, in the following video, you can see a signal modulation. we are sweeping a frequency range from 300kHz to 6GHz by VNA meanwhile applying 1V and 5kHz signal from signal generator to the bias tee built in the VNA.
Unfortunately, if I increase the 5kHz signal from the signal generator the bias tee filter the signal. How can I do this signal modulation? is there any specific bias tee, diplexer, or directional coupler for doing this job?
I am new in RF measurement and any suggestions are appreciated.
I need a passive device or a method in which I can apply these two signals in a signal modulation way.

Thanks.

 

[BradtheRad]

A volume control circuit might be adapted to perform AM modulation.
A JFET is an easy method to vary signal amplitude. It's depletion-mode which makes its usage simpler than enhancement-mode devices.

Simulation spun off from circuit found in Falstad's menu (animated interactive simulator). Volume control made from an N-jfet.

 

[D.A.(Tony)Stewart]

The bias T is just for adding a signal or DC bias. It does not multiply.