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f4cepl4nt

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  1. How would I go about analyzing a circuit such as the one below? I have a few questions to start with: 1) Do you consider the antenna an AC voltage source? 2) What is the purpose of C2? I'm assuming it's to reduce noise, but how exactly does it accomplish this? 3) If I wanted to use an NPN transistor instead of a PNP, would I just have to switch the diode and battery orientations? Along with capacitors if they are polar. 4) What is the ground symbol at the bottom of L1 connected to? Is it like the other half of the hertz antenna, or just connected to some big piece of metal, or what? One note: The capacitor on the schematic is a variable cap with a rating of 365 MMF, whatever that means. If someone could fill me in on what that means that would be cool too, because I got the schematic from a very old book
  2. Just a quick question or two.... does the sine wave output of a hartley oscillator (or colpitts or another sinusoidal output oscillator) create AC (does the output voltage go negative)? Or is it just DC with voltage moving smoothly up and down? Also, if I were to take a 1MHz signal from a square wave generator, (a 555 timer or another oscillator that just makes a pulsed DC output) , and transmit that with an EM wave; if I had a series LC filter on the receiving end would that properly pass a square wave(or at least pass a sinusoidal component of that square wave)? Thanks again...had a hard time finding info on these two questions. My guess would be that the LC filter would pass the sinusoidal component of the DC pulsed wave...and the hartley/colpitts/watever oscillator makes pulsed DC. Please inform me if these guesses are correct! =)
  3. Yeah there were a few sites in there that were kinda useful...though nothing that really explained how antennas work going WAY down to the basics. I'm still confused about how an antenna creates a current out of an EM wave hitting it...or does it? See I'm a little boggled about how antennas affect a circuit. To me, they just look like a piece of wire going nowhere, so how do they affect a circuit at all? I'll try to find a VERY basic circuit for a radio receiver, or if anyone can just throw one together and post it here that would be nice, and just give me a run down of how it works, focusing mainly on how an antenna affects the circuit. Again, nothing fancy, just the complete basics.
  4. Electronics Resources? We have a section like that? Link me please =) I just found an article section and didn't find much there on radio electronics. :) [EDIT] oh stupid me he was referring to the forums. Hey, good idea ante, thanks. Will definitely check that out.
  5. Despite the fact that I really appreciated the help you offered
  6. Hey again guys, in need of a bit of help again. In my robotics class at school (which basically turned out to be a electronics/ infrastructure physics class) we have a summative project due at the beginning of june, and I've got a great idea for the project (mine is a new security feature for a car). The only problem is, my solution relies on radio electronics to work at its best, and I'm completely clueless in that field
  7. Don't worry about it, I found out. It's about 450 uH Thanks for the help though ;D
  8. I need to build a coil with these specs: 1 inch length, .5 inch diameter, ferrite core, 30 turns of 22awg wire and 3 layers. Can anyone give me a pretty accurate measure of the inductance of that coil? This is for a capacitor charging circuit, and I've done a few calculations of my own but I figured I'd come to you guys for a little help to make sure I've got it right. I ended up with a value of 32.99mH, (.03299H) but that seems FAR too big to be accurate. Anyone with a more accurate calculation please fill me in :) Thanks again guys.
  9. Just a quick question: Lets say I have two transformers, one with a 2:1 voltage ratio and one with a 3:1 voltage ratio. If I were to hook these up so that the voltage gets increased twice, would the output voltage be 6 times as much as the input? Would the current follow the same pattern as well, being decreased by a factor of 6? Please answer these questions assuming no power loss...or give me an idea of how to estimate power loss in a transformer :) Basically I'm just wondering if it would work properly. ;D
  10. Hahahah its ok Audio, you've helped me enough over time that it compensates for that minor error thanks again ;D Oh yeah just one more thing: The output of the rectifier will still be pulsating rather than constant voltage, will that affect the charging of the capacitor? Is there any way to change that pulsating signal (From 0-~690V) to a constant voltage? Last question! Promise! ;D
  11. So the idea is plausible then =) Great. A small current of 1.8mA doesn't worry me, I have all the time in the world to charge a cap
  12. Hey guys, just doing some research into converting voltages, and I was just thinking: Would it be possible to say hook up a 9v battery to a IC555 timer, and connect the output of that timer to the primary winding of a transformer and connect the secondary winding to a high voltage capacitor? Just a thought...I've seen so many complicated charge circuits which I couldn't possibly hope to understand :o ;D Just let me know if my idea is completely idiotic or not. Hahahah Thanks
  13. Hey again everyone, just one simple question about transistors: Why do people say something like 'a transistor typically has .6V from its gate to its emitter and .2V from its collector to its emitter'?? Doesn't the voltage get determined by the rest of the circuit? Like for instance, if I put a 10K resistor connected to a transistors collector then saturate it, would there still be .2V between the collector/emitter? How about 100K? Or how about 1G? The way I'm understanding it, no matter how absurd your resistor value for that circuit, there will always be .2V from collector to emitter. (And the same goes for the base-emitter voltage, always .6V??) Thanks for helping me with this one, I probably have a few other transistor questions lingering in my mind but I'll look for those later
  14. Ok one last thing: I have a picture of a circuit here, and there is an opamp used, but there is no negative feedback to lower the output voltage Lets say the voltage across the resistor in the phototransistor branch is 1V and the voltage across the phototransistor is 11V when there is no light. That means that at the positive input on the opamp there is 11V right? The negative input on the opamp will always be 1.5V in this circuit. So then there is a 9.5V differential to be amplified. On the 358N opamp there is a gain of 100dB (which is 100, 000 times, just like audio said earlier) resulting in a 950 000V output. That can't be right, but there is no negative feedback to lower the output voltage down. Am I missing something? Or would that MOSFET just be blown to smithereens hahah :D That is my last question, I promise. Audioguru, you seem a wee bit mad at me, so I'm sorry if I'm asking stupid questions....but at least I'm being decent about it. It's not like I'm saying " Hey Guy5, wh3re ArE teh L33t 5chematICs U arE goin6 to snD me?!@?!!?11one!?" ;D
  15. Thanks for the help audio, but aren't bels arranged in a logarithmic scale? So wouldn't 60dB (6Bel) be a gain of 1 000 000 (10 to the power of 6)? You said that most opamps have a gain of around 100dB, resulting in a voltage gain of 100 000. Does that really mean the output of an opamp with it's inputs at 5V and 4V (1V total) will be 100 000V? Seem's a little bit big to me, but what do I know ;D One last question, if I were to apply a huge voltage like that (100 000V) to the gate of a MOSFET, would it destroy it? Or would it just be turned on like usual and run fine? Basically my question is, is there an upper limit to the amount of voltage you can apply to a MOSFET? Thanks again, a lot of the stuff I read about I don't fully understand until one of you guys give me a down to earth explanation of it :)
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