FM BJT Reactance Modulator (Proof on Oscilscope)
I would like to show you an experience on designing BJT FM Reactance Modulator circuit .Please take a moments to see my youtube video.
Actually,I am confuse with this circuit.I am not sure if this is an FM signal.Wheares,mathematically it is an FM signal.Bear in mind,that using BJT as reactance modulator have some nonlinear and some [cons and pros].Thus, you will see some noise in the modulation proccess.
So,do we have anyone who can confirming if this is an FM signal or just AM?
Please take a look to my video below:
https://youtu.be/2UKrWWMPyKQ
Your video appears to show FM modulation (second scope trace). Frequency determined by amplitude of an input signal (first scope trace).
Reactance has to do with capacitance or inductance, doesn't it? Do you mean that it arises directly from the BJT?
This concept is not a well known characteristic of transistors, is it? Or is it?
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Yes, it is coming from the second transistor which working as a Modulator or exactly as equivalent capacitance .
Here the most important thing we should do is to biasing the transistor in class A with another important point .It is required to set a high transistor input impedance to prevent loading colpitts circuit(the first transistor from the left).
It is well known concept that was used since 1960 when they were using vaccum transistors.
Today,In modern they usually using varactors.
Thanks for discussions.
I'm not motivated to watch a video. But every junction
is a varactor (of varying quality and kV).
There's modulation and there's modulation. If you only
need to see -a- response, many diodes would do. But
if you want -linear- df/dV, your choices are fewer....