I want to generate a 5 kHz microwave pulse to induce a sample signal. This microwave pulse has an underlying microwave frequency of 2 GHz. In order to investigate very tiny signals, which should arise within my setup with a frequency of 5 kHz repetition, I want to use a lock in amplifier to differentiate my 5 kHz signals from the noise floor.
Currently I have a Hewlett Packard 83640B signal generator 10 MHz-40 GHz and a Zurich Instruments lock in amplifier HF2LI.
Can I use the lock in for generating the 5 kHz reference signal, put it in the signal generator which is then modulated with 5 kHz and generates a 2 GHz signal by its own which is sent to a microwave antenna?
The detection signal of my sample is of course used as input for the lockin, it compares the input signal to its internal reference of 5 kHz, and shows me how big my sample signal is.
Is this possible? Which obstacles do I need to handle? Is there another way if this setup wont work?
I am no physicist and no engineer, please keep your comments rather simple if you have a tip or good advice.
Best Answer
I'm quite sure it is appropriate and practicable.
For modulating the generator, I have, however, some concerns:
In optics setups employing a lock-in often use shutter-wheels to modulate the (light) source; especially if modulating the source itself would be problematic or impossible (indandescent bulbs, daylight, starlight). That way continuously working (light) sources can be used.
The shutter wheel provides also the sync signal for the lock-in (e.g. from a separate fork light barrier).
Switching the signal after generation by shutter- (or reflector-) wheel (or other means more appropriate for microwave) has the advantage that the generator can work continuously avoiding artifacts by modulating it at generation (e.g. frequency/power instabilities).
Maybe this could be also important in your microwave application. Maybe not; if modulating the generator is not a problem.