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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 to differentiate my 5 kHz signals from the noise floor.

Currently I have a Hawlett Packard 83640B signal generator 10 MHz-40 GHz and a Zurich Instruments Lock In amplifier HF2LI.

My question is, can I use the Lock In for generating the 5 kHz reference signal, put it in the signal generator which is than modulated with 5 kHz and generates a 2 GHz signal by its own which is send to a microwave antenna?

The detection signal of my sample is of course used as Input for the Lock In, he compares than 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 =)

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    \$\begingroup\$ I'm not familiar with the HP sig gen, and the practicality of this is mostly going to hinge on getting the sig gen and LIA to trigger properly. But in general, it sounds like a good approach. What is the nature of the signal coming back from the sample? more microwaves? And what aspects of it are you interested in? delay? amplitude? you will lose most (but not quite all) of the internal structure of the return pulse. \$\endgroup\$ – Jack B Aug 15 '17 at 11:17
  • \$\begingroup\$ I'd like to agree with Jack - especially if you're not an engineer it physicist, I'd presume that there's a solid chance that the solution that you have in your head doesn't solve your actual problem. So, to avoid that, please also describe what you need to achieve in the bigger picture! \$\endgroup\$ – Marcus Müller Aug 15 '17 at 11:35
  • \$\begingroup\$ Thank you both for your opinion! The nature of the signal coming back is a voltage originally oscillating constantly at 75 kHz. But if my sample is interacting, it interacts of course with 5 kHz, so I will have a voltage with 5 and 75 kHz oscillation. If my sample does not interact, the 5 kHz signal is missing. So I am interested in the occurence of the 5 kHz, not the exact amplitude and not the delay. \$\endgroup\$ – Jacccy Aug 15 '17 at 13:05
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    \$\begingroup\$ It would be really useful to see a scope capture of the signal coming from the sample, showing what you want to measure. How quickly will the 5kHz signal change amplitude/appear/disappear? no quicker than 500Hz I hope. Either that or say what your sample is and what it is doing to the microwave pulse. \$\endgroup\$ – Jack B Aug 15 '17 at 16:31
  • \$\begingroup\$ It is a completely new setup under construction. I never have measured the signal of the sample, I cannot show you any kind of output. And I dont now the rise-/fall-time neither the amplitude. But I expect the signal to be smaller than my noise floor, therefore I need the LockIn. The samples' properties will be changed upon microwave exposure, and this change I want to detect. The detection process generates a voltage, which without interaction shows 75 kHz oscillation. With interaction I expact an additional 5 kHz oscillation. Unfortunately that is all I can say. \$\endgroup\$ – Jacccy Aug 16 '17 at 7:59
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You might use a function generator to provide the 5KHz modulation.

Then use a NE567 tone-decoder, with center-frequency set to 5KHz.

Just an idea.

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  • \$\begingroup\$ But than I lack the features of a lock in which filters out my signal from the noise =( \$\endgroup\$ – Jacccy Aug 16 '17 at 7:24

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