Fm transmitter

[karthikeid]

hi

can u modify this circuit with an electret mic and all the correction to work well because
i am looking for a smaller size transmitter  ???
the previous circuit u gave works fine too...but little big one

 

[audioguru2]

Simple circuits never work well because important things are missing.
This one also needs to have a regulated power supply because it is tuned by voltage. Without a regulated voltage the frequency will change as the battery runs down.

With a regulated power supply and a mic preamp with pre-emphasis then the circuit will not be small.

 

[karthikeid]

hi

can u post me anyone circuit here pls ???

 

[audioguru2]

hi

can u post me anyone circuit here pls ???

Electret microphone preamp circuits are on my hard drive but you can find them on Google.
Pre-emphasis circuits the same.
Voltage regulator circuits the same.
Do it.

 

[karthikeid]

hi

i have drawn the fm transmitter circuit with the preamplifier kindly provide me the operation of this circuit ???

View attachment 40709

 

[audioguru2]

You made many mistakes.
Your circuit will not work.

View attachment 40710

 

[Hero999]

Why don't you just use the circuit from the datasheet?

Always read the datasheet very carefully before implementing the circuit.

As you've realised, you need a pre-amplifier so why not just look up non-inverting amplifier on Wikipedia and change the resistor values to get the required gain?

To figure out the gain look at the datasheets for the transmitter IC and the electret mic.

 

[audioguru2]

The LM358 is too noisy (hissss) to be a mic preamp. Make a mic preamp with a low noise audio opamp like a TL071 like this:

View attachment 40711

 

[karthikeid]

thanks for the information provided i am update the complete circuit once i have build it...

 

[karthikeid]

what will be range of transmission...will this be a better transmitter ???

 

[audioguru2]

what will be range of transmission...will this be a better transmitter ???

You didn't post a better transmitter.

The MAX2606 has a low supply voltage and a low supply current so its output power is low. Its range might be a few hundred metres to a very sensitive home stereo tuner or car radio with nothing in between or across the street to a cheap clock radio.

 

[karthikeid]

how this circuit works can u explain audioguru  ???
will this be efficient??

View attachment 40819

 

[audioguru2]

how this circuit works can u explain audioguru  ???
will this be efficient??

It is a garbage circuit that causes interference on many frequencies. It will barely work as an FM transmitter because its 9th harmonic (96.3MHz) is at a very low level.

Its fundamental oscillator is at the 10.7MHz of the crystal filter. It is a squarish-wave with many harmonics and the 9th harmonic (96.3MHz) is in the FM broadcast band.

 

[karthikeid]

i am really confused what to do, i need a stable fm transmitter circuit and it must be smaller in size.... someone pls help ???

 

[audioguru2]

i am really confused what to do, i need a stable fm transmitter circuit and it must be smaller in size.... someone pls help ???

The MAX2606 FM transmitter IC comes in a small surface-mount package. It operates at a low current from a low supply voltage so its range is only about 20m.
Here is a project: http://electronicsprojects.mediadir.in/?p=1879

It is missing pre-emphasis equalization so it will sound muffled (no treble frequencies) when heard on an FM radio. View attachment 40825

 

[Hero999]

It depends on what you're doing.

How good does the transmitter need to be?

Is it just a simple listening device which only needs to be telephone quality or is for a singer's mic. which needs to sound crystal clear?

If all you want to do is build a simply listening device a simple two transistor FM transmitter will do. It doesn't need pre-emphasis or anything fancy.

If it's a singer's mic. then you need a high quality amplifier with pre-emphasis.

Either way the circuit originally posted is a bad idea because it will generate lots of interference on other radio bands.