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Everything posted by walid

  1. walid Hi 4-1000A I see from what you said that the mod. index is affected by: 1- the freq. of the modulating signal and 2- the amplitude of the modulating signal. if this is the case, how can the designer control or achieve the desired mod.index he want. AND is it correct if we say that controlling the modulating signal amplitude by using a variable resistor can control the mod.index thanks.
  2. No No No Audioguru you copy and paste part of that article which i can't understand. This article looks like Text books that we learned in university, these text books talk about things in the other world. I need simply to tell me like this: "this diode is like any diode have a K & A and it is measure high resistance in the two directions if we are in absolutely dark room...." My question again: What happen when IR ray strikes this diode? Is it become short circuit? Are there any differences if we connect it in reverse, that is kathode inplace of anode and vise versa. THANKS
  3. Hi ateso8634 if you have a 10k ohm 3 terminals trimmer you can use it instead of the 2 terminals one. look at the 3 terminals trimmer's terminals, they look like a triangle there is one is far and two close, connect (short) the far one with one of the remaining two then you have two terminals trimmer as you want. hope this help you.
  4. hi 4-1000A your answer is excellent but still one point: in your example you calculate a mod.index 5 i know now (after your answer) that i can control this by varying the amplitude of the modulating sig. what is the best mod.index if i construct a FM Tx what is the optimum mod.index
  5. hi prateeksikka please tell me more about the modulation index we choose if you can or point me to sopme related web page.
  6. Don't forget the diode, a rectifier diode it must be connected in parallel to the coil
  7. I hope you can solve this problems, we all need you to be with us all the time your friend Walid
  8. I read the article that explains photodiodes but it is very long and very difficult to understand. I'm too young to read this high level article. what i want is to answer my questions mentioned above please thanks
  9. No problem I talk with a designer from USA and he told me that he rarely use the oscilloscope, the understanding more important than instrument or come first. yours walid
  10. Thats what I expect from you Audioguru. it is a good answer thank you very much
  11. walid


    Hi Alun I read in some web page that we can match the final stage with the antenna using matching C-L-C If you want i give you the address
  12. No Alun, I believe that AUDIOGURU is the king of this community and he can answer any electronic question. May be he buisy (worked)
  13. No no no Alun If i removed one from some board and want to reuse it how can I identify its K &A
  14. Thank you Alun i hope somebody else tell us the remaining two
  15. If I have a photodiode on my table, how can i identify its cathode and anode using didital multimeter? tanks.
  16. In some circuits I see four 20MHz crystals in series or sometimes in parallel! What's equivalant value then?
  17. Hi AUDIOGURU Where are you................I wait your answer thanks
  18. What are these abbreviatives mean: QRP QSO NFB circuit thanks
  19. To AUDIOGURU (1) Quote [1) I built the circuit that someone complained about, it didn't work with a new 9V battery, and also didn't work when the battery was a little old.] Are you mean that when the battery become less than 9V old (2) Quote [2) I added a low-dropout voltage regulator so that the supply voltage for the audio preamp and oscillator transistors was stable until the battery was dead] Are you mean by low-dropout voltage regulator that regulator small size looks like small signal transistor or what? (3) Quote [4) It had no treble so I added proper pre-emphasis like radio stations use.] please what treble and pre-emphasis? (4) Quote [i used good-at-high-frequencies 1000pF ceramic supply bypass caps.] Are these caps polyster caps or what? (5) Quote [i was amazed that it sounded so good. When it transmitted the sound that it picked-up from my home stereo playing an FM radio station, it sounded exactly the same as that station when received on my good car radio.] It seems that you put your home stereo near the Tx MIC not connecting it internally to your Tx.
  20. To Staigen (1) Quote [i usally dont calculate coils and resonanses the way you did here, i use a nomogram for this.] I also use MATHCAD program, i made many pages to calculate any thing like LC and others, but i do what you see because there are other people read what we are writting so I put them into my account. (2) Quote [You almost always have to tweak the coil to get the right freq in a circuit like this, or you can get a adjustable coil(usally reduce Q) or, like Audioguru did, get a trimcap] I know that stretching the coil decrease L and compressing it increase L. I don't understand this "usally reduce Q". This you will have to explain a little bit moore (3) Quote [A 4) strays! They can easily lower the freq that amount] I think stray capacitances are not taken into account during calculations, and their effect can be compensated by making the cap variable or L. (4) Quote[This you will have to explain a little bit moore] you said this when I try to ask about this: I think that (not sure) only the three caps to the left with L making the LC circuit, then this group connected to the next stage (T1 and related components) through the 1nF. I know that if we agree about this the freq will be more than 133MHz and this will increase the problem, but i can't accept the three caps to the right to be a part of the LC circuit. please STAIGEN explain this for me. thanks.
  21. i want mor info about designing a VCO to Audioguru only put the analysis and calculations of you FM Tx cicuit
  22. Hehe thank you staign but still........
  23. I go to the 3W FM transmitter project which uses five RF chokes==> L2,L3,L5,L7,L9 5 6-hole Ferroxcube Wide band HF Choke (5 WDG) but i can't understand anything from this "6-hole Ferroxcube Wide band HF Choke (5 WDG)" can you explain? thanks
  24. OK OK guys it is 100uH coil and i can't purchase it, can i use a piece of ferrite rod and wound some turns on it? IF this OK what values (rod length and diameter, n turns etc)
  25. Hi Staigen Thank you very very much for this great explaination Ceq = (1/(1/20pF+1/3.9pF))+15pF+(1/(1/1nF+1/20pF+1/10pF)) as you said Ceq = (3.2636pF) +15pF+ (0.8696pF) ceq = 19.133 pF Now there are three caps to the left of L and three caps to the right of it. To calculate L i use this equation: L = 0.001 N2r2 / (228r + 254l) where L is the inductance in henrys, r is the coil radius in metres, l is the coil length in metres (>0.8r) and N is the number of turns. from: http://www.ee.surrey.ac.uk/Workshop/advice/coils/air_coils.html In FM Tx the auther give these values about the coil: phi =7.2 mm, n = 3 so r = 7.2/2 = 3.6 mm 0.8 r = 2.88 mm, so length of coil must be > 2.88 lets take it 3 mm ==> L = 0.001 (9)(1.296 E -5)/[(228 * 0.0036) + (254 * 0.003)] L = 1.1664 E-7 /[ 0.8028 + 0.762 ] L = 1.1664 E-7 /[ 1.5648 ] L = 0.7454 nH freq.= 1/[2 * pi * sqr(LC)] = 1/[2 * pi * sqr(0.7454 nH * 19.133 pF)] = 1/[2 * pi * sqr(1.42617 E -18)] = 1/[2 * pi * 1.19422 E -9] = 133.27 MHz which is out of the intended band (88 - 108 MHz) Three propabilities: 1) a mistake in my calculations 2) the assumption that the capacitance of the varicap is 20 pF is wrong 3) the coil must be larger value Still one point: I never think that the three caps to the left of the coil are in relation to the LC calculations. and still unbeleive thougy the serve to enlage the total C (parallel) and lower the freq. why not to look at these three caps with L as an independent stage that connected to the folowing (T1) through a coupling cap 1nF. I think that the auther think that way.
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