Audioguru FM Tx

[walid1]

Thank you guru it was a very good answer

What question I forgot to ask about?

thanks

 

[awash]

Audioguru C1 and C3 = 330N I got only one 330N cab I replace the other one with like 470 n or should I have make the same capacitor for both please help me to solve shortage of one 330N cap . and LM2931 is it the switch ? to break the +ve tterminal ? cose i saw the ground wire conncted with it accourding to ur diagram i got kind of confused . just littel brife like always u do fast and remarkable help .

thanks so much

 

[audioguru2]

C1 and C3 = 330N I got only one 330N cab I replace the other one with like 470 n or should I have make the same capacitor for both please help me to solve shortage of one 330N cap.

They are just audio coupling capacitors. A higher value will pass lower audio frequencies. 330nF passes frequencies down to about 40Hz, 470nF will pass audio frequencies down to 28Hz and 220nF will pass audio frequencies down to 60Hz, with the impedances of the circuit. Their values don't need to be the same. Use 100nF if you don't like deep bass.

and LM2931 is it the switch?

What switch? The LM2931 is a low-dropout 5V regulator in a small transistor plastic case. It still regulates very well when its input voltage drops to 5.5V which a 9V battery can do. An ordinary 7805 regulator needs an input voltage at least 7.5V to regulate properly, but the voltage of a 9V battery quickly drops to about 7.2V then drops slower to lower voltages.

to break the +ve tterminal ? cose i saw the ground wire conncted with it according to your diagram i got kind of confused.

The regulator has an input, an output and a ground. It is used to supply regulated 5V to the mic preamp and to the FM oscillator so that they don't change when the battery voltage runs down.
The mic preamp makes distortion or doesn't work with a different voltage and the FM oscillator's RF frequency changes with a different voltage.

 

[awash]

thanks for fast replay  and one more help again . i cound not find 2931 in my area can I use 2903 which have  8 pin and if i can use it plz tell me which pin i have to use to put in in place of 2931?

thanks again

 

[audioguru2]

The only 2903 that I know is the LM2903 dual comparator IC. It is not a low-dropout voltage regulator.
All semiconductor manufacturers make a 5V low-dropout regulator in a small plastic transistor case.

 

[walid1]

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 

 

[audioguru2]

In fact i use An ordinary 7805 regulator with a table power supply adjusted to 9v.

A 7805 works fine with an input voltage of 7.5V or more.

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

A cheap radio overloads and makes the transmitter appear at many places on the dial. My Sony Walkman FM radio does only when its antenna is switched to Distant. It does not overload when it is switched to Local. My homw stereo tuner and car radio don't overload from my FM transmitter.

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

A 2-wire electret mic connected to the 1st transistor then its output connected to your amplifier should work. Remove C4 to stop the treble boost.
The DC voltages of the 1st transistor should be something like these:View attachment 39547

 

[walid1]

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

 

[walid1]

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 

 

[audioguru2]

Hi Walid,
12V is a very high voltage for the circuit.
With 9V, Q3 has an average of 9V across it and an average of about 40mA through it. Therefore it dissipates about 9V x 40mA= 360mW.
With 12V, Q3's current will increase to about 53mA. Therefore it dissipates about 636mW. The max dissipation allowed for a 2N3904 transistor is only 625mW so it is burning out. 

 

[walid1]

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

 

[audioguru2]

Hi Walid,
Since your circuit transmits hum then maybe your wires are too long and are picking up mains hum.

It is important to have very short wires in circuits for VHF frequencies. Side by side wires have capacitance between them. Wires have inductance caused by their length. Extra capacitance and inductance messes up VHF radio circuits.

My FM transmitter is made on stripboard with each track shortened by cutting with a drill bit. My transmitter is 5cm long by 3cm wide. The wires are about 2mm long and the wires on the electret microphone are about 5mm long.
The pF capacitors are ceramic disc with very short wires, the nF capacitors are film and the uF capacitors are electrolytic.

My FM transmitter sounds perfect, can transmit all sounds heard in a room and has a range to a good FM radio with nothing in between of more than 2km.

Good luck with stopping the war in your country.

 

[awash]

The only 2903 that I know is the LM2903 dual comparator IC. It is not a low-dropout voltage regulator.
All semiconductor manufacturers make a 5V low-dropout regulator in a small plastic transistor case.

audioguru am building ur fm project but still i coundt  get LM2903 so i think it use to make the supply voltage stable when the battry getting down  ? so can i try with out LM2903 but with the new battry for instant ? and what should i do with that capacitors they are in parrallal to use LM2903 . please tell me the correction to get full working of  ur Fm with out LM2903 . thanks again

 

[audioguru2]

audioguru am building ur fm project but still i coundtView attachment 39582

 

[walid1]

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

 

[awash]

audioguru am building ur fm project but still i coundt  get LM2903 so i think it use to make the supply voltage stable when the battry getting down  ? so can i try with out LM2903 but with the new battry for instant ? and what should i do with that capacitors they are in parrallal to use LM2903 . please tell me the correction to get full working of  ur Fm with out LM2903 . thanks again

ohh ...my bad ..
Sorry audioguru i i thoght i typed  LM2931 . ( then the above post corrected instady of  LM2903 just placed LM2931 ) .
still i dont think i can get what u told me 78L05 or 7805  i will try to get one .
but is there any way to use ur Fm with out voltage regulator  ?

 

[audioguru2]

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

My FM transmitter was in the open window on the 2nd floor of my house. My house is near the top of a hill. It transmitted a few hundred meters to my cheap Sony FM Walkman radio and more than 2km to my good car radio. Other houses in between blocked the signal which went the farthest with nothing in between the transmitter and the radio.

 

[walid1]

Hi guru

I HOPE U READ IT ALL

I understand u but i intend to use this inside a building of 4 floors, i want to talk while move from place to place, may be inside the lifter ........

when i first test it with that problem mentioned above my son talk near mic inside a room while i'm going away from the building, i hear him at about 150 meter and still hear the transmitter noise at more than 300 meter, there are many things in between.


I want to spend any time to succeed, but i'm afraid from that after spending this time and still have those problems of stability; its freq moves away
and the human body affect and the clearness of the received voice

In my work I have pair of wireless (about 200 meter) with LCD and 8 channels and some functions like outoscan..... i remove its cover to take a look, one second and i quickly close it, it contains many SMD ICs and tiny parts, i feel not OK, disappointed, in fact it is one of my big dreams to build one pair with one function TX and Rx voice with good fidelity and range.

Now  I ask u some questions:
1) you said the antenna must be about 80 cm long, is it important the diameter of this wire and if it have a plastic cover or not; that is can i use a 1.5 mm wire like that used in the electrical power connections

2) to reduce human body effect why not to enclose the oscillator stage inside a metal can like tunner used in TVs

thank you audioguru

 

[audioguru2]

i intend to use this inside a building of 4 floors, i want to talk while move from place to place, may be inside the lifter .

My circuit has a low power and might be blocked by concrete and the metal in a lifer.

still have those problems of stability; its freq moves away

It is better than most other simple transmitters but it doesn't have a crystal like good transceivers.

the clearness of the received voice

My transmitter is extremely clear. But it is very sensitive. Maybe you are talking too loud or are too close to it. Make the received sound no louder than a radio station.

1) you said the antenna must be about 80 cm long, is it important the diameter of this wire and if it have a plastic cover or not; that is can i use a 1.5 mm wire like that used in the electrical power connections

Antenna wire diameter doesn't matter. Mine has a plastic cover.

2) to reduce human body effect why not to enclose the oscillator stage inside a metal can like tunner used in TVs

I didn't try a metal box but it will probably be better.

 

[sssaaa]

hi audioguru
your fm transmitter output power is 230mW or 360mW?(at 9volts)
and on what minimum mAmp at 9V your transmitter work good.