Jump to content
Electronics-Lab.com Community


  • Posts

  • Joined

  • Last visited


Everything posted by walid

  1. Hi the folloing fig is the front end of a simple AM radio reciver It contains the AM ferrite antenna and two variable caps, one connected // to the primary coil of the antenna and the other // to the primary coil of the red (local oscillator) transformer. AM sig freq from 530 KHZ to about 1600 KHz is tuned and go to the base of the transistor through 20n cap. the local osc connected to the emitter through 10n cap. its freq is always higher than the AM sig by 455 KHz. the o/p of this mixer at the transistor collector is 4 signals: the two signals and sum and the difference. That was a simple summary of circuit. My question is that i need a simplified explanation of the work of this mixer? thank you very much
  2. First I used the dictionary for translation so please forgive that there were some errors in language OK, I'm engineer in communication and control, 5 years in university after high school , Despite this, I feel myself as if I'm small and stupid pupil when discuss [glow=red,2,300]GURU[/glow]. I know many of Engineers, and dealt with through the hundreds of forums, and even in this forum did not find a better than [glow=red,2,300]GURU[/glow]. Obtaining a degree in engineering is required, but not enough. The world needs a genius like [glow=red,2,300]GURU[/glow], does not need papers written in it a certificate in engineering. Why take advantage of the engineer does not understand anything and does not have something to offer to society. For all these reasons, I find that even [glow=red,2,300]GURU[/glow] right to criticize any person manner it/he deems appropriate when [glow=red,2,300]GURU[/glow] says that, I believe this because [glow=red,2,300]GURU[/glow] said that. Do not think I crazy or naive, in the community that I live in, we have a saying heritage states : [glow=red,2,300]"Who taught me a characters I was a slave to him " [/glow] Only [glow=red,2,300]GURU[/glow] taught me milions of characters and was patient on my often mindless questions. In the end, I say to all that [glow=red,2,300]GURU[/glow] precious wealth of scientific I hope to preserve and benefit from him Ask God to extend his life And live happily with his family. thank you [glow=red,2,300]GURU[/glow] thank you MP Thanks to all Forum members
  3. Hi I believe that Mr. [glow=red,2,300]AUDIOGURU[/glow] is a big R&D Engineer, and he is the best one i meet in a forum OK i'm not so good in electronics, but I can distinguish between person and person, and I know from the answer the person's abilities. Therefore, I ask everyone to deal with Mr. AUDIOGURU courtesy and respect because he deserves it thanks
  4. thank you guru Summary of what guru said: (1)Pre-emphasis: a process is being carried out at a transmitter to boost high audio frequencies (2)De-emphasis: a process is being carried out at a reception side to cut the treble audio frequencies back down to normal and cut hiss at the same time. (3)Why do they boost the treble audio frequencies at the transmitter? If a transmitter doesn't boost the treble audio frequencies then a radio will cut them and it will sound bad, like a stereo with its treble control turned all the way down. I have a few questions: (1)Why remained an American used the same pattern despite the tremendous progress of technology? (2)Why they need to boost then cut, if they didn't cut at the reciever they haven't to boost at Tx? (3) (a) 2.1kHz: Is it from MATHCAD curve or from your design and calculations? (b) RC = 75us: RE * C4 = 470 * 150n = 70.5us? © 3.2kHz (1khz (RC= 50us) : RC = 50us is ok but what are these two frequencies? (4) Our region (Israel-Palestine) is closer to Europe. If I did my calculations to design the first stage pre amp And went to the selection of this C4 value, then I have to use (RE * C4 = 50us)? (5) The following Fig is drawn using a cwCAD III I want to watch the freq response But I do not know how to do it, can u please tell me. I want that to compare between Math calc and swCAD results. (6) You told me once: How the freq response be flat if we know: Xc4 decrease when freq increase XC4// RE is also decrease with f so Av increase linearly with f ?! thank you audioguru
  5. Hi GURU From the above values of C1 and C3 and the corresponding values of the freq they can pass, I deduce that u assumed or calculated the i/p impedance of the first stage and the second stage to be 12K. For the 2nd stage: you did these calculations: So u concluded that Zin = 21.6K RC filter freq at that Zin = 1/(2 pi R C) = 22 Hz and not 40 as u said> For the First stage u concluded that the i/p Z is about 10K and so the cutoff freq = 33Hz and not 40 NOTE: I am not looking for mistakes to say that this is a mistake, I feel the forest when I find a contradiction. I studying this discussion often without any comment and every time I understand more things Thank u guru for everything u teached me
  6. Finally, after a long discussion with Mr. Audioguru, i discover that the frequency response is a relation (curve) of freq vs voltage gain (Av). The following Fig is the 1st stage of guru's FM Tx: Av = RC/re, this is assumed at very high freq that makes Xc4 = 0 so shortened the RE But at audio freq (30Hz to 15KHz), Xc4 changes from about 35k at 30Hz to about 70 ohm at 15KHz. So, RE (=470 ohm) can not be considered as shorted by C4 at all freqs RE//XC4 range from 61 ohm at 15kHz to 464 ohm at 30 ohm Av = Rc/(re+[RE//XC4]) changes with freq I wrote a MATHCAD commands to look at this effect of C4, her is it: And her is the results: the strange thing is that the freq response is look like this: with some knees (3dB) my curve has not a knee From my MATHCAD curve, I can see that C4 bossts the hi freq signals more low freq signal please comment and explain this difference for me http://NOTE: I'm sorry i made MATHCAD for C4 = 100n and discuss for C4=150n It'll take long time to correct this and to upload the new fig thanks
  7. I think but not sure the following: You know that C = e0 (A / d) where A is the area of the capacitor plates, and d is the distance between them. e0 is the permittivity of free space (8.85X10-12) a) Vo is still as lt is cause the relation did not affected by batt voltage. the capacitance of a capacitor will is a fix value when it is manufactured> b) capacitance, C: as d increase C decrease by the same factor (10 times) cause the relation is inversly proporetional the following link ia a calculator to see by yourself http://micro.magnet.fsu.edu/electromag/java/capacitance/ c) electric field, E: V = Ed = (F/q)*d = Fd/q= W/q, since q (the charge) is at the demonator then E increased 10 times d) electric flux density, D: I don't know may be later I can found somthing e) charge, Q: from the relation (Q = CV ) we see Q is directly proportinal to C, so Q is decreased 10 times as C f) charge density: is decreased 10 times as Q g) energy stored, U: W =
  8. Hi I read carefully Kevin Weddle's reply an Audioguru's reply, but sorry i can't understand anything, i don't know why. Also I can't ask questions because i don't know about what to ask! Despite that will ask : how 20v and the supply voltage is only9v????
  9. Thank you guru, I think that this is a big subject it is better to focus now on topics simple and and when finished turn to the more difficult topics. I want to tell you that a great honor for me to debate with you, you great wealth of scientific.
  10. (1)I know that it is a common-base amplifier because of C5 connected between base and GND and at FM freq it short that base to GND. But I did not know about the transistor's alpha, can u please tell me something about it? (2)I attach your FM Tx, I look at Q3, it is a 2N3904 transistor and it deal with 100MHz signal to amplify it. How it can do this with only hfe =6 at 100MHz? thank you guru, I wish that I'm not disturbing you by these frequently questions.
  11. Please I want further clarification on this point, I hope to support that with examples and illustrations thanks
  12. Hi I understand how FM, AM and PM modulation takes place If allowed to give us an idea of IR modulation thanks
  13. thank you guru from what you said, if the o/p impedance of the first stage = 9K and the i/p impedance of the next stage = 1k and the signal is 1V only (1/10) of that signal reach to the next stage that is 0.1 volt. If so, the word dowenload be inappropriate because I understand that the characteristics of the first stage change!
  14. Hi I'll back to the first design; C_E without CE. I think in the past that increasing the value of Ic have better property to get higher o/p power, and I was prefering -according to this- to design circuits with higher Ic values GURU explained that this was a mistake and from my discussions with him I found that the disadvantages of this selection: 1-consumption of the battery rapidly 2- more Ic = less hfe 3-i/p impedance to less with more Ic This leads to download the previous stage My questions : (1) Are there any other disadvantages? (2) when I have to choose higher values for Ic?
  15. hi Today, I sat thinking at this point, what happens when the i/p impedance for the subsequent stage is less than the o/p impedance of the past stage? Please clarify the idea Thank you
  16. Hi Ft is the freq at which beta (hfe) = approx 1 for 2N3904 transistor I found that at 300MHz, hfe = 1 frome the same datasheets i found the following curve: look at the red curve at 300MHz, hfe = 5 dB 20 log (hfe) = 5 hfe = 1.8 Now at FM freq (say 100 MHz) and from the red curve, hfe = 15dB that is hfe = 5.6 (very low) In the past, when I was looking for a FT, and I find it = 300MHz, I think that hfe would be a big value at FM freq = 100 MHz but it seems that the curve will be worth only about 6 My question: Is this enough when using this transistors as oscillator at 100MHz? gURU use that transistor in his FM TX. thanks
  17. Hi guru I can use SWCAD III to see the freq responce of a C-E transistor amplifier circuit, But I want to know how are calculated or how is expected during the design process Can you please explain to me thanks
  18. thank you guru it is a complete answer
  19. Thank you guru I understand you The author said that the voltage drop on a red led is 1.6v Is this standard value I measure it , it was 2v and sometimes 2.2 volt thanks
  20. Hi I feel I am alone with this question. But in any case, I built the circuit and worked excellently. The question remains puzzled me is the importance of R1 (=470 ohm) when i tried to remove it, the red led is illuminate It remains as to whether or not there is a salt solution can anyone explain to me the function of this R1 thanks
  21. Now I have a Specific question which is: comparing the folloing figure: with this figure (salt0001): Noting that the voltage at pin 1 (Vo) = (e2-e1)(R2/R1) I note that e1 = 1.8 V e2 must be Slightly lower than e1, say e2 = 1.7V so Vo = (1.7-1.8)(220K/10K) = - 2.2 V If the solution resistance is increased, then e2 will be lower, say, 1.5 V so Vo = (1.5-1.8)(220K/10K) = - 6.6 V In all cases the o/p Vo will = 0 V because we supply LM324 with a single power supply. Either the equation (Vo) = (e2-e1)(R2/R1) is wrong and must be (Vo) = (e1-e2)(R2/R1) Or the design is wrong?????
  22. I am sorry I forgot to thank elix for his interest and involvement Thank you very much
  23. Hi dear guru you are absulutely true You are wonderful, you are the better man i have dealt with him in the electronics you our great teacher, thank you very much Yes, using two supply bypass capacitors at the 555 fixed the problem Whatever I said I will not be able to express my deep gratitude to you
  24. Hi guru Yes I forgot to attach the schematic of the "person detector" that drives the LED The schematic is attached below from: http://www.electronic-circuits-diagrams.com/alarmsimages/alarmsckt19.shtml As u see, it is a Tx and Rx I used one IR LED and not two I put the two units in front of each other and not beside as the designer said My module is on until some one pass so I replace the NPN transistor by PNP one I did not use a relay, the emitter of PNP connected directly +9V and collector connected to a RED LED through a 680 ohm resistor The main o/p is taken from the collector point to the pic Now, I am not interested in pic (microcontroller) When I walk in between the two units and stop for a moment (This possibility can happen in practice ) the LED (and so the o/p) is Intermittent lighting glows irregular What can I do to change this o/p to be one short 5v pulse Thank you guru very much
  • Create New...