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How to detect AM modulated signal using a spectrum analyzer: Case of higher frequencies

goroks

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Hi everyone! Hope you are all keeping safe and healthy.

I am trying to detect a terahertz (THz) signal at 350 GHz modulated at 200 kHz with a sine wave. However, no matter what I try I am not able to detect any signal. The synthesizer uses a 9x multiplier and there is no mixer unit at the spectrum size.

I was able to check the back-back detection by directly connecting the RF output of the synthesizer with the RF input of the spectrum analyzer. Here I used a signal at 1GHz modulated at 200 kHz. and the signal was detected with no problem.

Any comments/ideas to share on such measurements? Anything would be very helpful.

Thanks in advance
 

dick_freebird

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350GHz is way outside normal, even most leading
edge RF test gear. Capacitances will shunt it away.
I have yet to see a mixer product that claims to work
with a 350GHz input (200MHz LO, no prob).

Here's an "easy" one - can you detect CW 350GHz?
With what equipment?
 

vfone

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So, you are able to detect a 1GHz signal and you cannot detect a signal having the frequency three hundred and fifty times higher?
You think that those frequencies are close enaugh to be compared?
 

biff44

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maybe if you sketched the block diagram of how you are trying to measure this, we could comment then.
what you described in words does not make any sense at all.
you will either need to find a spectrum analyzer that has these words on the front of it "1 MHz to 400 GHz", OR you are going to need to downconvert your 350 GHz signal with a mixer and some sort of local oscillator. And even if you DID get a setup to work, it would "detect" the AM by showing sidebands on the carrier. You would still need to do more (like look at the envelope of one of the IF stages in the spectrum analyzer)

Do you have any 350 GHz rated diode detectors? They would look like a waveguide input, and a BNC or SMA connector at the output. You could hook a detector output to an oscilloscope and detect AM modulation.
 

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