problem in oscillator part

[maxparveen]

hello everybody. i need your help here .
i am making a fm transmitter of range 1 km .schematic is attached .now problm is that it only amplifies the input signal   not do modulation.  i think problem in osilator.
can u tell me how to make proper coils since i m using copper wire which i have bought from a motor winding shop.and for capacitor i m using trimmer (0-50)pf . please help me out .u can send me another tested schematic also whose range is about 1.5 to 2 km.  i have no license problem here :-\

 

[audioguru2]

Hi Max,
The text in that very old project tells you exactly how to make it.
It operates at a very high radio frequency where capacitance between two wires is too high and wires are inductors. It won't work if it is made on a breadboard.
It must be made with very short wires on a pcb or on stripboard with extra track length removed.
Here is one that works beside one that doesn't work:

 

[maxparveen]

hello and thanks audioguru for guidline.
  now i ll prepare it  on pcb.but can u tell me my coils are ok or not about which i have asked earlier.and u r saying it is an old circuit so please suggest a new circuit for fm transmitter ranging 1.5-2 km.i ll try that old circuit also but prefer the new one  provided by u.it will be really helpful.

 

[audioguru2]

I used American parts for my FM transmitter. Can you get American parts in your country?
This is the schematic with parts numbers for my FM transmitter:

 

[maxparveen]

hello audio guru


i can only get very commonly used american IC s  here .
i ll prepare that transmitter in one week and tell u the results.  u havent told me about coils i have prepared with enameled copper wire  used in motor winding .are they going to be work properly...rest of parts except lm2931 are available of good quality so tell me substitute for that .. i have my own LCR Q METER TO TELL THE EXACT VALUES FOR COIL  BUT PLEASE tell me how to mak these  perfect
also tell me the range for that transmitter(value for C4  to get maximum range)  here there is no licencing problems for students like me .and i have not to use the transmission for music.i need this to send some DTMF s and encoded digital signal... .  i ll also use same for monitering my room in absence....so please  guid me to make a good fm transmittter since i have to make several projects based on it.

regards.

 

[audioguru2]

RF circuits at high frequencies must be made with very short wires to reduce capacitance between parts. Also long wires have too much series inductance for high frequencies. I used stripboard and other people have made a pcb.

All semiconductor manufacturers make a low dropout 5V regulator like the LM2931 that I used. It allows the battery voltage to drop down to 5.4V before it drops out of regulating. An ordinary 7805 drops out when its input voltage is less than about 7.5V which is a fairly new 9V battery.

I used 1mm enamelled wire to make my coils. Don't measure their inductance, just make yours the same.

The value of C4 is determined by the amount of pre-emphasis (audio treble boost) that is used by FM radio stations in your country and your FM radios have de-emphasis that matches it. Phone an FM radio station to ask if theirs is American or European.

The range of my FM transmitter across an empty river valley to a very sensitive FM tuner is more than 2km. Its range to my Sony Walkman FM radio is about 300m. Its range to the garbage FM radio from The Dollar Store is across the street.