walid

hi guru What did u mean by:"has a range to a good FM radio with nothing in between of more than 2km." nothing like what thanks

hi audioguru i can not discribe exactly what going with me but i'll try hope that u understand me 1) when i tune it to some freq i noticed that it be in a wide region that is it cover from 97 to 102 MHz, strong at the center and gradually weak to other sides 2) the recieved sound is 80% hum (very strong hum) and about 20% voice, my son talking hallow hallow and i heared him as some thing (rag) inside his mouth, anyone cann't accept this voice 3)when i take the receiver away and walk i can hear that voices only 80-100 meter 4) the Tx very senseitive to any touch or any body near to it 5) when i disconnect C3 i hear pure voice like that when mic faced an amp speaker I use 220n//100nF as 330n =C3 I wait your help hoping this Tx work to use it in my walky talky thank u guru very much i want to tell u that we have electrical power only 7 hours a day since 2 monthes this is one of the reasons that make my job very slowly because ISREAL destroying the main generators which supply all GAZA strip I respect everyone in this world and cann't hate anyone but tell you only to know as a good friend for me, yours

Hi again At first i hear my self near 106 MHz but it very weak voice strong noise then few seconds later Q3 was very very hot my power supply now is 12 volt 7A small battery why Q3 is so hot thanks

Hi I do what guru told me, isolate the amp circuit and remove C4, then measure voltages at points mentioned at the above figure and i had the following results: Vcc 4.96v VB 0.74v VC 2.43v VE 0.12v AT MIC 3.14V not 2v as guru when connecting my 10 watt amp and talking near the MIC i hear my voice clear and strong ......... now i'll going to connect this first stage to the entire FM Tx to see what will happen thanks

Hi Jean-Noel Welcome to our forum 10 years ago when the electricity company suplied us only 170vac instead of 220, i had a step up transformer. One day it burned and emitt abig amount of smoke i decide to rewound it and simply did the following: got a paper and a pen to write notices open its cover and take a long look disconnect all connections and make any sign to help u in the reconstruct process unwound the wire noticing the direction of wound and the number of turns take it to shop and ask him the same wieght and diameter when i wound it by hand and because i was harry the turns were not side to side so it take more size than it must, so i reduce the number of turns by about 10% for each step finally it work and i had a very good results and i believed from that time that there is no critical Now I ask you to share with us your formulas

There are many things, ROM, RAM, ALU, buses ....etec there are a huge number of sites that talk in detail about this subject and u can easily find them using google

The circuit shown below is from: http://www.redcircuits.com/Page86.htm For me, it is easy to analys any circuit containing npn transistors, but i'm confused when come face to face with pnp type i read this in the same page: Circuit operation: The circuit is inserted between the supply and the load, therefore, until a trickle-charging current of at least 100µA is flowing towards the load, D1 and D2 will conduct. The forward voltage drop (about 1V) available across the Diodes, drives Q2 into conduction and, consequently, Q1 will be cut-off. If no appreciable load is connected across the circuit's output, Q2 will become cut-off, Q1 will conduct and the Piezo-sounder will beep. Assume that I insert this circuit between a 13.7v charger and a small 12v battery, can anyone explain what will happen at first and when the batt is fully charged. thanks

Hi In fact i use An ordinary 7805 regulator with a table power supply adjusted to 9v. when i build it the first time on [a special board for experiment that with holes] i noticed some big short circuit, but after solving this problem and assuming that all was OK smell and touch all parts for heat .... i begin to talk near the mic but nothing During the tunning process on the FM radio receiver I hear a strong noise in more than 3 places, but near 100MHz was the big noise related to the transmitter I then assume that the problem is before the oscillator, mic or the 1st amplifier i change some parts and check the connections, but still no voice recieved I have a 10 watt amplifier, i want to disconnect the FM Tx from the Q1 o/p and connect this point to my 10 watt amp to check if these stages are ok .................. i do this but no voice out of the speaker advice me thanks

Thank you guru it was a very good answer What question I forgot to ask about? thanks

Hi I know what is an amplifier, but what the meaning of HiFi thanks

Hi all my friends, and special HIIIIIIIIIIIII to audioguru Now and finally i am going to build this FM Tx , yesterday i put all the components on the table and today afternoon i'll put them together my question is if i build my own receiver using TDA7000 or TDA7088 to receive signals from that TX ... another way, I want to talk with my friend 100 meter far away, i need 2 units each contain TX and Rx If I tune Tx1 to 100MHz and Rx1 to say 80MHz, so, Tx2 to 80MHz and Rx2 to 100MHz I know that to each fundamental freq there are some harmonics, when, some day i build my first transmitter i hear myself in many places along the 88-108MHz band I am worry from that in the sme unit the sender hear himself If this occur my project will fail ans so my efforts so please tell me and advice me how to do this and what must i do thanks

I agree because this exactly what they teach us in schools guru start by this answer to force andrie to use his mind, guru is a good man with NPN Tr we connect collector to point more positive than emetter and make the tr ON by aplying a +tive voltage >= 0.7 V with PNP Tr we connect collector to point more negative than emetter and make the tr ON by aplying a -tive voltage <= -0.7 V

e) When Ic is high (look at Fig VD01 below) hfe (beta) is low, Zin is low and VBE is high (Look at Fig VD02 to see how VBE changed with IC) f) When Ic is high it will drain your batt quickly NOW I want (as u may noticed in the figures) that Ic = 2mA 2mA means Isat 4mA 4mA = 9/[RC+RE] [RC+RE] = 9/4m = 2250 RC= 10 RE ==> 11RE = 2250 ==> RE = 204.5 ohm take it 200 ohm (two 100 in series) so, RC =10 RE = 2K ohm NOTIC your Zo = RC = 2K, so Zin2 must = 20k at least to not affect Av1 STEP 2 For symmetrical swing up and down, VCE = VCC/2 = 4.5V Remain 4.5V from the 9V batt, these 4.5V divided between RC and RE according to their values 4.5/11 = 0.41v, so, V(RE) = 0.41V and V(RC) = 4.5 - 0.41 = 4.09V The number 11 arise from the fact that RC contribute by 10 and RE contribute by 1, total=11 STEP 3 At Ic = 2mA, beta = 200 so, IB = 2m/200 = 10 uA Id (the current pass through R1 and R2 with no transistor connected) = 10 IB = 100uA Id = VCC/[R1+R2] = 9/[R1+R2] ==> [R1+R2] = 90 K We calculate VE as = 0.41v and from the curve VBE = 0.64 SO, VB = 1.05V I(R2) = Id - IB = 90 uA ==> R2 = VB/V(R2) = 1.05/90 u =11666.7 ohm take it 12 K ohm R1 = 90 -12 = 78K , connect 68K in series with 10K STEP 4 Zin = R1//R2//[hfe*(re+RE)] re = 26 mV/IC = 13 ohm so, Zin = 10.4K // 42.6K = 8.4K (fairly low i'll discuss this later) the o/p voltage can swing from [VCC] up to [VC- Isat*RE] down, that is it will swing from 9V to (4.91 - 4m*200)= 4.11v this swinging ac signal is carried on a VC dc voltage The max upper peak of this signal which represent the negative part of the i/p ac signal, = VCC - VC = 9 - 4.91 = 4.09 V The max lower peak of this signal which represent the positive part of the i/p ac signal, = 4.11 V Note the symmetric it is very close to 100%, thanks to Mr AUDIOGURU for every thing. To increase Zin, u have to lower IC and recalculate the other values. Later I'll continue my discussion about: bypassing the whole RE bypassing part of RE choosing the caps value between stages discussing a real designs and show if this is good or bad ... I hope guru read this and put his golden comments thank u all WALID

hi all Hi audioguru... my big teacher I'll show you here what guru taught me in the last 5 pages, then we'll continue to reach a high level... hope so WHAT I WANT (1) design a preamp (voltage divider unbypassed) (2) using the famous PN2222A transistor whose datasheets are attached below (3) I need a voltage gain of 10 for low distortion. (4) I have a 9v batt as a power supply (VCC). CALCULATIONS and ANALYSIS STEP 1 Av (the voltage gain) = RC/RE = 10, so RC=10 RE and V(RC) = 10 V(RE) Before u choose RC and RE values u must consider the following: a) the value of RC = o/p impedance (Zo) b) If this stage have a load like a second stage follow it then the total Zo= RC//Zin2 C) Zin2 must be >= 10 RC to not load down the 1st stage and decrease its Av d) IC = IE = Isat/2 , where Isat is the saturation current and we choose its half to be at the center fore symmetrical swing of the o/p signal Isat = VCC/[RC+RE]

Hi I back again to this very important subject first thank you audioguru you do a good work to make me understand i print this 5-pages subject after editting it in WORD and finally have 19 A4 pages i take it with me every where reading them. it is hard to read directly from the computer screen, i need to underline the important and new aspects and compare bwn some replies When I finish it I'll either put a detailed design or continue asking question and god help guru walid

OK Mr audioguru I may understand the general aspect of what u said but can u give me an example about this especially on your FM transmitter circuit. where the subcircuit or the parts that do the pre-emphasis also in the receiver where it be placed in the whole circuit thank u audioguru

i understand that it require a separate FM receiver i use this link but i have not any results but in this http://www.alldatasheet.com/ i faound many i'm not understand this statement thank you

(1) I read carefully the CM8870 datasheets but I can't conclude that it can receive the FM signal directly or it must be connected to a separated FM receiver please tell me (2) I hardly got the datasheets of CM8870/70C, but i really have CM8870PI Is there any difference? thanx

This is also my problem, how to relate what you study with the practicle projects if u can't you waste five years in a universty all text books, net and persons talk about every thing but not about what you want i hope someone help u and me

also my car does it without my attention, but i discuss for theory and then for using this theory as a designer, i told you that i live to learn To indulis thank you very much

Please send a copy to me at

yes, its a 3 cells Lead-acid batt

I'm sorry, lets forget what i said before and start again .... the emergency neon lamp has a rechargable 6v rectangular batt if i want to charge it using 7.5 to 9 volt power supply and want to stop the charging process when the batt is fully charged using a voltage comparator at what voltage i must stop thank you Hi Mr Muhammad Abu Bakar, in fact i want to learn about batt charging and how the designer make a decesion in chossing his components and not to measure temperature and ave time yours walid

ok ok ok i want to tell you that i recharge unrechagable batteries for years and reuse them it is never explode i have not faced any problem with them and after recharge them the last long time specially in remote control and sound toys i want that info to stop the charge process whe it must stop can you help me?

audioguru i go to where you point me but nothing my question is very simple forget that it is charger assume that u connect a fully charged 3v batt to a 5v ps and measure the voltage across this connection what is your reading? thank you