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# walid

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1. ## 10kHz FM modulation

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. ## IR photodiode

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. ## Re: what is trimmer

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. ## 10kHz FM modulation

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. ## 10kHz FM modulation

hi prateeksikka please tell me more about the modulation index we choose if you can or point me to sopme related web page.
6. ## relays - SPST, SPDT, DPST, DPDT?

Don't forget the diode, a rectifier diode it must be connected in parallel to the coil
7. ## MIC coupling capacitor

I hope you can solve this problems, we all need you to be with us all the time your friend Walid
8. ## IR photodiode

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. ## A chock coil

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. ## 100 uH coil

Thats what I expect from you Audioguru. it is a good answer thank you very much
11. ## Antenna

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. ## MIC coupling capacitor

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. ## Photodiode terminals

No no no Alun If i removed one from some board and want to reuse it how can I identify its K &A
14. ## What are these abbreviatives mean

Thank you Alun i hope somebody else tell us the remaining two
15. ## Photodiode terminals

If I have a photodiode on my table, how can i identify its cathode and anode using didital multimeter? tanks.
16. ## crystals in series or parallel

In some circuits I see four 20MHz crystals in series or sometimes in parallel! What's equivalant value then?

18. ## What are these abbreviatives mean

What are these abbreviatives mean: QRP QSO NFB circuit thanks

21. ## Voltage control oscillator VCO

i want mor info about designing a VCO to Audioguru only put the analysis and calculations of you FM Tx cicuit
22. ## Voltage control oscillator VCO

Hehe thank you staign but still........
23. ## 100 uH coil

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. ## 100 uH coil

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. ## Voltage control oscillator VCO

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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