Tuesday 20 August 2019

How can AM modulation be performed in LTspice by built in MODULATOR function?


I have been looking for this for an hour and there is no single example or information about it in English language. The nearest ones are like this and there is no explanation I don't even know it is correct. No tutorial, no example, no diagram ect.


I used search still no luck:


https://www.google.com/search?biw=1422&bih=655&tbm=isch&sa=1&ei=kV0EW7fHG8OwsAGa7YyYCg&q=am+modulation+ltspice&oq=am+modulation+ltspice&gs_l=img.3...151628.151628.0.151831.0.0.0.0.0.0.0.0..0.0....0...1c.1.64.img..0.0.0....0.EcFpzqH5i3c


As an example how can we modulate a 1k carrier signal with a 10Hz signal by using the the built-in MODULATOR? (AM not FM)



Answer




As stated in the help:



The MODULATE device is a voltage controlled oscillator. See the example schematic .\examples\Educational\PLL.asc. The instantaneous oscillation frequency is set by the voltage on the FM input. The conversion from voltage to frequency is linear and set by the two instance parameters, mark and space. Mark is the frequency when the FM input is at 1V and space is the frequency when the input is at 0V. The amplitude is set by the voltage on the AM input and defaults to 1V if that input is unused(connected to the MODULATE common).



So you place that component, connect the bottom port to GND, and write the frequencies you want into the Value part in the format of mark=xyz space=abc mark will be the frequency when 1 V is supplied to FM and space the one when 0 V is supplied.


At the AM port you just put some sine or whatever:


Working example of the modulator


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