audioguru fm transmitter

[awash]

Thanks again Audioguru please coudnt get this “15:1 attenuator with 2 (mono) or 3 (stereo to mono) resistors" could you show me the picture and I will try to find from my old junks. 
Or
I got some circuit on the net to change Dynamic microphone to electret microphone
Do u think it works perfect? And I don

View attachment 39384

 

[audioguru2]

The transmitter needs only 10mV of audio from an electret microphone. The output from a dynamic microphone is a little less, so it needs a preamp to increase its level.
The output from your CD player is about 150mV so needs an attenuator (voltage reducer) to reduce the 150mV to 10mV.
Two resistors in series make an attenuator. Two resistors connected together convert stereo to mono then a 3rd resistor makes them an attenuator.
R1 in the project powers the electret microphone and will need to be removed.
Here is an attenuator:

View attachment 39385

 

[sssaaa]

Increase your battery's voltage to 9V and the range will be much farther. Also, decrease the value of the 470 ohm resistor to 220 ohms.

The antenna should be about 80cm long, in the same direction as the radio's antenna. The radio should also have an 80cm long whip or 160cm long folded dipole antenna or rabbit's ears and be very sensitive.

The difference between using 12pF instead of 10pF is nothing.

hi audioguru
i want to know that what will be the out put power of this circuit in  mW  when we do these changes.
thanks..

 

[audioguru2]

hi audioguru
i want to know that what will be the out put power of this circuit in

 

[Silicon]

yeap that wasp circuit gived about 20m range for me too,and it consumed wery little.. in fact the only thing i was happy about that circuit is frequiency stability,the voice sensitive was wery bad,it really would be suitable only for hand-held microphone... 20m in the same room(not tru walls)unsensitive mic so u wont get oscillation with U radio... hey it's not a bug...o and btw when i count tank circuit to work at about 100mhz and calculating tank circuit only with tank circuit capacitor/tuned capacitor values i found my wasp work at about 60Mhz...

yes my post is about that yellow circuit given somewhere around in this topic

bla bla try too kill Uself

 

[audioguru2]

when i count tank circuit to work at about 100mhz and calculating tank circuit only with tank circuit capacitor/tuned capacitor values i found my wasp work at about 60Mhz...

It is inaccurate to calculate LC values for a tank that operates at VHF or above.
How much is the stray capacitance across the coil, trimmer capacitor or other parts connected to them?
How much is the capacitance inside the transistor?
How much is the inductance of each piece of pcb track or wiring?
How tightly wound is the coil?
Etc?

 

[Silicon]

in recent post U had said that  capacitances,i dont remember exactly but it was calculated as i said not counting other values i said that for others to know,at lowest frequiency windings were tight,anyway o dont care about that transmiiter anymore becoz i sold it and buy ..em... U know and Im think i had learned enough from that transmitter. o btw does chip voltage stabilizator consumes any power itself?(i'm not about voltage drop trough it)

 

[audioguru2]

does chip voltage stabilizator consumes any power itself?

Of course it does. Look in its datasheet. It is typically 2mA with the 10mA load of the circuit. You can buy lower power voltage regulators if you need them.

 

[sssaaa]

If Q3 is operating in class-C then the output power is more.

I connected R8 to ground instead of to the positive supply but I didnot get good results, then I connected R8 to positive then the circuit gave good output.
why the circuit hadnot given more output when i operate Q3 in class-C?

 

[audioguru2]

The oscillator signal is small, it comes from the oscillator's emitter.
When Q3 is a class-A amplifier then it is biased and ready to amplify it.
When Q3 is a class-C amplifier then the input signal must have an amplitude of at least 0.7V before it amplifies it.
I didn't try it but Q3 might be a good class-C amplifier if its input is larger from the oscillator's collector. Then a reversed diode across the base-emitter of Q3 would be needed to stop the coupling capacitor from charging.

 

[sssaaa]

from which technique the RF cops will get any transmitter?
some one tell me that they use Radar ?
is it Right?
if any one "ON"(start)any illegal transmitter they will caught him in minutes or it takes time?

 

[sssaaa]

And one more question with thanks.
i use trimmer but they are little big. i want to use like urs.
i have scrap of some clocks in which clock i will find them?

 

[audioguru2]

from which technique the RF cops will get any transmitter?
some one tell me that they use Radar ?

Radar won't work.
RF cops are alerted by people complaining about radio or TV interference. The RF cops use their van with a directional antenna on top and their receivers to find the transmitter causing the interference. The interference will occur if your transmitter operates at the same frequency as a radio or TV station or if its harmonics do.

if any one "ON"(start)any illegal transmitter they will caught him in minutes or it takes time?

If they are listenng for the interference with their van and at the same time you are continuously transmitting the interference then they will catch you.

i use trimmer but they are little big. i want to use like urs.

Mine are nice and small, from a local electronic parts store. Digikey also has them.

 

[sssaaa]

this is the only(directional antenna) technique, or other military or other secret sevices use different  techniques and equipments.
i m asking you these things because in my country there is no good law for these things for example if some one make tansmitter for hobby, educational or leaning that how it works and transmit & if they (police or RF cops) catch him they dont listen or understand any argument they dont see who is he student or learner, they catch them and put in jail for many years there is no law for students

 

[audioguru2]

Here in Canada, the RF cops don't put anybody in jail and they don't chop off heads like the cops do in some crazy countries. They would explain about interference and ask that the unlicenced transmitter be turned off. Just a warning the 1st time.
The 2nd time they would probably take away the transmitter and the owner would need to go to court to explain about it.

 

[sssaaa]

The RF cops use their van with a directional antenna on top and their receivers to find the transmitter causing the interference

this is the only(directional antenna) technique, or other military or other secret sevices use different  techniques and equipments?

 

[audioguru2]

I don't know what the military or secret police do. Maybe they shoot people or cut off the heads of people who transmit without a licence. ;D

 

[abcpet]

to mr. Audioguru,
I want to build this, but I have some questions about it ( how the schematic compares to the picture)

I see 14 capacitors in the schematic, but I seemed to only counted 13 capacitors in the picture of the completed picture

I see some bigger power? precision? resistors on the picture. What power rating, etc should they be?

What do the 2 vari-caps do?
I'm also really unsure about what capacitors to use.


Thanks really much

 

[audioguru2]

I see 14 capacitors in the schematic, but I seemed to only counted 13 capacitors in the picture of the completed picture

C2 and R6 are on the bottom of the circuit board. I didn't make a new circuit board but I modified the mod3 circuit into the final mod 4 circuit instead.

I see some bigger power? precision? resistors on the picture. What power rating, etc should they be?

All resistors are 1/4W, 5% carbon film. My 220 ohm resistor is longer because it is about 40 years old.

What do the 2 vari-caps do?

I used two 5pF to 35pF trimmer capacitors. C6 tunes the RF oscillator to the frequency you want to use and C13 peaks the output at that frequency.

I'm also really unsure about what capacitors to use.

The uF capacitors in my schematic are electrolytic, nF capacitors are metalized poly film and pF capacitors are ceramic disc.

 

[abcpet]

"metalized poly film"
could I just use standard film/foil cap?
wouldn't film/foil also be better