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 Homework Statement:

I've been given a small challenge having been shown a some waveforms and a bit of data. I am very new to this area but I must utilise DSP to condition and process an analogue voltage measurement. I don't know what the waveforms are from and I wasn't told so that I couldn't just search it.
What I'm attemtpting to digitise is a pulsed sinusoid. I'll add a couple of drawings to this post to show what I'm trying to explain. But I have a variable duty ratio, frequency and voltage depending on the impedance of the purely resistive load. These waveforms can also be combined for intermediate effects on the load. However, I'm most interested in the voltage and frequency properties.
I have a voltage range of about 500μV to 1.5V. Combined with a frequency range of 50 Hz to about 12 Mhz. So, I think my teacher want me to apprecciate the difficulties of having such wide ranges of operation. I need to digitise this analogue measurement so that I can find RMS values, peak values and such.
 Relevant Equations:
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I'm thinking that Im going to need something like a low pass filter around 100 Hz so that low noise disturbances from a nearby PSU and such won't disturb my sampling. However, the unit will have to operate around 50 Hz sometimes. Is it possible to use a Fast Fourier Transform to filter out frequencies below 100 Hz most of the time, but then simply "disable" this when measurements dip below 100 Hz? And if so, assuming the frequency is low and say my voltage is low, what is the optimal way to filter out this gaussian noise when the noise and measurement magnitudes and frequencies are somewhat comparable but signal remains dominant.
Then in terms of my ADC, given the voltage ratio of something like 3000:1, does this just mean that I will need to adjust the number of bits to limit my quantisation error for voltage but if I want something like a max of 1% error, I have to compare this to my minimum measurement and then reevaluate as necessary? But for low voltage values I think I need to consider minimum voltage for ADC, so I may need to boost the voltage.
Apologies if anything is unclear or simply incorrect. I have only done very basic signal conditioning and processing but I want to learn more. So, if you feel redirecting me to a link on theory will be most beneficial, that is fine. Thank you.
Then in terms of my ADC, given the voltage ratio of something like 3000:1, does this just mean that I will need to adjust the number of bits to limit my quantisation error for voltage but if I want something like a max of 1% error, I have to compare this to my minimum measurement and then reevaluate as necessary? But for low voltage values I think I need to consider minimum voltage for ADC, so I may need to boost the voltage.
Apologies if anything is unclear or simply incorrect. I have only done very basic signal conditioning and processing but I want to learn more. So, if you feel redirecting me to a link on theory will be most beneficial, that is fine. Thank you.