Very good. I've been researching and this is the best I've come across. The app I want is to have laser beam interrupted by a swinging pendulum. That feeds into an Arduino to get times of swings. The output being binary One thing I picked up on is your comment on stray lights. That's given me the idea of a filter of the right colour on the detection side. 1. Are there reasons to use a combination op amp and comparator chip? 2. Is there hysteresis in the circuit? 3. If there's bounce on the output I presume I can use a low pass filter?
I initially thought it would be due to the trace parasitic inductance from the 15V supply to the collector of the transistor which formed an LC oscillator with the collector-emitter parasitic capacitance. If all else would have failed I'd have added a ferrite bead around the pin of the base.
Is there any way to make these filters have a sharper curve? There are some strong VDL2 blips on 136.7 MHz that overload the SDR, Meteor LRPT is much more affected as each time these blips appear the meteor demodulation loses sync. Or is there a way to make a notch filter with a similar design?
I don't really understand how the concept of ensuring that the series equivalent resistance being smaller than the internal resistance of the crystal degrades the high Q of the crystal? Why does that condition need to be met??
Note: one doesn't absolutely need precision resistors - 1 trimpot used in the feedback loop of the rectifier opamp *or* one trimpot to adjust the input weights into the inverting adder is enough to balance out any error in the other resistor pair.
I don’t think the explanation of the mixing in the beginning is really accurate. It’s rather mathematically involved specially in an analog environment.
Your analogy starting around ~1:25 is one that would have confused me back when I was in school. Mainly the fact that you're using a digital device to describe analog behavior, and if when I was new to the topic it may not have been obvious why or where your analogy breaks down(Or I might not recognize it as an analogy and take it very literally), or even that you really intended to discuss analog signals and not digital. Just my 2 cents.
Wow. I've been using this exact configuration for crystal oscillators for decades without ever really understanding it, & this is the first explanation I've ever seen that's ever made sense to me. Thank you so much!
This video just started playing out of nowhere while i was replying to comments. I wansnt even watching anything to begin with. It’s wild because it’s exactly what I needed to know. Im building a radio. Right now im trying to amplify 4mhz active crystal and its not working. The crystal by itself is louder than adding a transistor or fet. I didn’t play around too much with bias and I didn’t do any filtering. I used an antenna and resistor or i used a transformer and antenna, I even just shorted it with antenna. I figure it should at least be louder than the crystal even if poorly implemented but maybe not. Another round of testing today. Maybe the chips im using can’t handle 4mhz but I didnt think that was particularly fast for a run of the mill semiconductor pulled from old monitors. Today ill try making my own oscillator I guess. Also would help if i had my 50mhz scope.
