telephone transmitter again not working??

[aimans]

made this fm telephone transmitter and it doesnt work. :'(
cant pick-up anyhtin on the radio, can anyone explain to  me why? ???

replaced Q1 with BC547, and Q2 with KN2222, rest all components unchanged.

 

[mvs sarma]

Hi.
check the PIN out data for the replaced components-- whether this aspect istaken care while soldering them?

what are the voltages measuredt at the respectiveTransistors?

 

[audioguru2]

I think the parts are too far apart on your PCB which causes high stray capacitance and inductance.

The project has a PCB that is much smaller than yours. Why not make it exactly the same?

 

[aimans]

i soldered the replacements with the correct PINs i kept that in mind had their datasheets while soldering them. i also didnot use "tinned copper" wire as the site told[i thought that it will not make a lot of difference] ami correct??

I think the parts are too far apart on your PCB which causes high stray capacitance and inductance.

The project has a PCB that is much smaller than yours. Why not make it exactly the same?

sure i will make it like the original nice and small, i made mine in a hurry,

 

[audioguru2]

Two coils have their turns tight together and their wire must be enamel insulated. The other coil has its turns spread apart so it doesn't need insulation. Tinned wire is easier to solder but the circuit doesn't need tinned wire.

 

[aimans]

Two coils have their turns tight together and their wire must be enamel insulated. The other coil has its turns spread apart so it doesn't need insulation. Tinned wire is easier to solder but the circuit doesn't need tinned wire.

exactly, i thought of the same thing and did not worry much about the tinned copper coil,

 

[aimans]

yes i made it agian and failed again in this fm transmitter, this time i corrected most of my previuos KNOWN mistakes but nothin on the radio. just cannot figure out why, my friends say i need someone to teach me!

this time i replaced Q2(2N3563) with BC547 and the other transistor is the same, didn't have 5.6pF so replaced it with 5.8pF, i dont think that is the problem though.

i calculated the inductance of the coils according to the instructions given, and they wre not at all close to those mentioned in the instructions[at the bottom of the page http://www.uoguelph.ca/~antoon/circ/FMTelTx/telephon.html ], so i just made the coils as it was given  and not the values given,

can someone help me in this thing i am very frustated with this phone transmitter, i tried them about 10 times but to no avail, someone please help me out here,

 

[audioguru2]

The pins layout on European transistors like the BC547 are reversed from American transistors like all the ones shown.

5.6pF is a standard value. 5.8pF is not. The circuit will work with a capacitor value from 4.7pF to 10pF.

 

[aimans]

The pins layout on European transistors like the BC547 are reversed from American transistors like all the ones shown.

yeah even i noticed them in the datasheets, i'll reverse the connections and try, but what if it doesnt work again?????

 

[aimans]

sorry, the thing is still not working, reversed the pin connections, i dont know what is wrong, please help me, someone, if anyone /?
has time i can even post my circuit to someone interesed so that you can help me out when you have time?????????

 

[audioguru2]

Sorry,
Your pics are too fuzzy to see anything wrong with your project.
I designesd and made my FM transmitter (the second one I have ever made) and it works perfectly:

 

[aimans]

thanks a lot for the circuit, i will surely try it adn let you know, i hope it works as i am not sure whether LM2931 is available here, and then later try the phone transmitter, and i will try to post a better pic as i am at takin pictures

i dont know if this is a stupid question or not but i'll ask as i have already asked naive ones before: is there any way your circuit can be converted into a phone transmitter? :

 

[audioguru2]

The radio frequency of the telephone FM transmitter depends on the supply voltage from the telephone line and the current of the phone you are using with it.
My FM transmitter has a known radio frequenvy because its oscillator has a 5V voltage regulator.

Everty phone line has a different voltage so you won't know what RF frequency it transmits on.
That is probably what your problem is.

 

[aimans]

\
Everty phone line has a different voltage so you won't know what RF frequency it transmits on.
That is probably what your problem is.

hmmmm, that is very interesting, is there a way i can stabilise the voltage using an LM317, or that wont help?

 

[audioguru2]

The telephone transmitter is modulated by the fluctuations in the telephone line. If you stabilize the voltage then it won't be modulated.

Maybe it can have a voltage regulator then the RF oscillator could be fed through a 620 ohm resistor and have the audio from the telephone line capacitor-coupled to it.
But the telephone line's voltage might not be high enough for the telephone and this transmitter drawing current plus some overhead voltage for the regulator and series resistor.

 

[aimans]

But the telephone line's voltage might not be high enough for the telephone and this transmitter drawing current plus some overhead voltage for the regulator and series resistor.

this means that it cannot be done successfully, not a problem,

i will measure the different p.d's around the phone line and post 'em here, and then the circuit can be modified accordingly, is this possible?

 

[audioguru2]

If you are far from the telephone exchange then your off-hook voltage will be low enough to operate a single telephone. If the phone draws a high current and you are far from the exchange then your voltage will be too low to also power the bug transmitter.

How can you modify your telephone company??

 

[aimans]

If you are far from the telephone exchange then your off-hook voltage will be low enough to operate a single telephone. If the phone draws a high current and you are far from the exchange then your voltage will be too low to also power the bug transmitter.

if that is the case then i can use a 9V battery to power the transmitter while connected to the phone line,

what do you think about this battery thing, will it work?

 

[audioguru2]

If you power the telephone transmitter from a battery then it will either stop the phone from ringing or it will be destroyed by the high ringing voltage.