Electronics-Lab.com Community # walid

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## Posts posted by walid

1. ### How to distinguish between FM and AM transmitter circuits

Thank you Hero999, you helped me

To build an FM transmitter which doesn't produce much AM, you need to use a varactor diode as part of the tuned circuit, rather than altering the bias point of the base.

Like this circuit? Another question:
Why the transmitter frequency change when the battery goes down, despite that the calculation of LC tank frequency does not doesn't take the value of the battery into account?
thank you alot
2. ### How to distinguish between FM and AM transmitter circuits

hi
please look at the following circuit, the author claim it is AM transmitter: it is from: http://www.zen22142.zen.co.uk/Circuits/rf/amtx.htm

it is look exactly FM Transmitter, the only difference is in the values of capacitors and coils!!!
Is there another difference I did not watch?
Are both circuits were the same?
thanks alot.

3. ### Is it a hartely oscillator??

The hartely oscillator has many drawbacks as do ther other simple oscillators. It could have to do with the resonant frequency of the LC and the ability to get high enough gain.

It may also have to do with any change in load conditions that could prevent or stop oscillation.

what if we use a buffer circuit between?

thank you KevinIV
4. ### LC tank circuit frequency

Hi
when you build a FM transmitter with  LC tank circuit the frequency is:

f = 1/(2 pi square root LC)
why then when battary goes down the frequency is altered in the receiver?

thanks

5. ### Is it a hartely oscillator??

Like this:

i understand you the reciever sense the carriar if ther is a cariar it do somthing like moving forward if no carriar do somthing else.

thank you guru

6. ### Is it a hartely oscillator??

Thank you guru it is good and fast answer
Now you this is only an oscillator niether AM nor FM
what you think it used for?
thank you guru

7. ### Is it a hartely oscillator??

Is this circuit using a hartely osc.? 1- is the emitter resistor affect the frequency of oscillation?
2- this is a transmitter circuit, is it FM or AM and why?

thank you very much.

VC or VCE?

9. ### question about symetrical swing

Hi
when i want to design a preamplifier using BJT and need to have a maximum symetrical voltage swing at the output, then two conditions must be satisfied:
1- VCE = 0.5 VCC
2- I (saturation) = 2 IC

Is there other conditions must be taken into acount?

I wait

Hello
When one design  preamplifier using BJT voltage-divider unbupassed Emitter config, one want max symetrical signal swing at the collector. To do this, VCE = 0.5 VCC &
I (saturation) = 2 IC = VCC/(RC+RE)
If I want a voltage gain = A, then

A= RC/(RE+re), where re = 0.026/IE, so

RC = A(RE+re) --------------(eq.1)

as said before, for max symetrical signal swing at the collector,

2 IC = VCC/(RC+RE)  ==>

RC = (VCC/2IC) - RE  ------(eq.2)

From (eq.1) & (eq.2) we get:

A(RE+re)= (VCC/2IC) - RE, solvig for RE yields:

RE = {VCC/2(1+A)IC} - (A/A+1)re

question #1: Is there any error in either equations or concepts

12. ### a cap vlue????

Rs in series with Zin

13. ### a cap vlue????

Whick R
Rs , Zin or both
if both, in parallel or sereise??
thank you

14. ### a cap vlue????

Hello
I built an audio amplifier that has an input impedance of 12k ohm my source signal was 1 mV and internal resistance Rs=1.2K ohm what the suitable value of the  capacitor that must be inserted between?
thanks alot.

15. ### How does this simple circuit operate?

Thank you hero999 it helped me

16. ### How does this simple circuit operate?

Hi
this is the circuit thanks

17. ### reshaping a signal

Hi
I need a circuit that  when the upper signal is in, get the out signal at the output
thank you if the phoito is not appear. the input sirnal is a dc positive pulses and the needed output is dc contenuous

Hello

Q1)
If the received signal frequency = 100 MHz, then the local oscillator equal 110.7 or 89.3 MHz?
thanks

19. ### question about Low Pass Filter

The 4.7nF capacitor creates a lowpass filter with the unknown value of the source resistance.
The 10k resistor and 6.8nF capacitor create another lowpass filter.

If the cutoff frequency of both filters is the same then their total is -6dB because each filter is -3dB.

If the cutoff frequency of both filters is  not the same? is it sitll -6dB
thanks
20. ### Transistor collector current

A transistor needs to have a high collector current (and a high base current which reduces its input impedance) and a low resistance collector resistor when it is in class-A and it needs to drive a low resistance load.

Are you mean like emitter follower?
What about a voltage divider configuration preamp. is there a situation here that we want a high IC current?
I stay, think long time about it, choosing small current (IC) give us a high Zin a long batt life and a transistor works in light duty, why not choose a very small current like 0.1 mA or even 10 uA, i know that big resistors will be used but this is no broblem!
thanks alot.
21. ### Transistor collector current

Hello everyone
We all know that Input Impedance decreased when we choose a high collector current, and that is ok
I want to ask: When one choose high current?
thank you

22. ### electronics

Hi
If you read the discussion in the following link will return you the great benefit
http://www.electronics-lab.com/forum/index.php?topic=4705.0

23. ### Electrolytic Capacitor

Thank you guru
I really miss you

24. ### Electrolytic Capacitor

Hi
Why an Electrolytic Capacitor explode when connected in reverse mannar?
thank you

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