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Having read the datasheet of LM7171, I have 7 suggestions: 0) is your scope fast enough (500MHz) to look for oscillations of the OpAmp 1) operate the OpAmp from 10Volts; its not characterized at onl …

Having thought through the direct downconversion issues, the primary challenge is the dynamic range needed to accept massive energy alongside the weak FM signals. simulate this circuit – Schema …

What is the SNR Signal Noise Ratio? For perfect synchronization, with I and Q mixers, filtered with "boxcar" sin(x)/x filters that match to NRZ (on, off) data, then only ONE sample per symbol will s …

For 0/180, if you track the carrier (RF, IF) phase, you'll only need a single-phase local-phase reference. For +60/-60, for optimal BER you'll need inphase and quadrature, so you set up matched filte …

Take that signal, run thru a limiter, and multiply the two signals in a mixer, with low-pass-output filtering.

You might achieve more sensitivity by operating a diode with 1uA or 10uA of bias current. A 1 MegOhm resistor from +9 volts will do this. For reduced capacity, use a small leaded resistor?? You need a …

If you have a large ratio between the highest frequency of the information, and the carrier frequency, then you might set the RC time constant at the geometric_mean midpoint between the carrier period …

You want MEMORY of the prior frequency information, in the Loop Filter. Give the loop filter 10uSecond timeconstant, so you begin to learn what depends upon what.

The input clamp protects the downstream amplifiers, in the case when the keyfob is too close to the transmitter. Dynamic range of these keyfob 125KHz data links is 100,000X in voltage (100dB). Regar …

You also asked about an Envelope Detector using only transistors. I assume the 2 transistors have similar VBE at the same current. The pot allows some adjustment for threshold. If you cannot set Vout …

Once you have the various I+Q samples, you need to execute an FFT. Plus other "cleanup" steps. The Wikipedia page states 20MegaSamples/second for 4 us, thus 80 samples. Round up to 128 samples. If I …

GMSK has 4 symbols, 2 involving frequency changes, and 2 with frequency held constant. Because the GMSK is (ideally) constant amplitude, the vectors move only around the outside (circumference) of th …

I implemented a synchronous demodulator on silicon. Why not? Used a PLL to track the incoming phase and frequency. The PLL ran at 4X incoming carrier, ensuring a 4-phase JohnsonCounter provided precis …

Try this simulate this circuit – Schematic created using CircuitLab

You've given no specification for modulation bandwidth versus carrier. The finest way to extract AM modulation is the synchronous detector using a mixer to combine the AM-signal and a fixed-amplitude …