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Simple & Powerful FM Transmitter(only one transistor)

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zlatkoMM

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Re: Simple & Powerful FM Transmitter(only one transistor

If you want simple FM transmitter try this one:
 

    ajex

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Re: Simple & Powerful FM Transmitter(only one transistor

zlatkoMM said:
If you want simple FM transmitter try this one:
The pre-emphasis provided by R1 and C2 is cancelled by the lowpass filter of R2 and C4 and C5.
To make it a little better:
1) Change R1 to 27k and change C2 to 2nF.
2) Remove R2 and C4.
3) Change C5 to 330pF.

The values are for the 50us equalization used in Europe, Australia and New Zealand.
 
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ajex

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Re: Simple & Powerful FM Transmitter(only one transistor

zlatkoMM said:
If you want simple FM transmitter try this one:

Thanks brother, how make L2 coil? can we use IF ferrite core (in FM radio)for making this coil. If u have please give a PCB for this circuit and can you tell me what is the distance that we can use to transmit..

Added after 3 minutes:

Audioguru said:
zlatkoMM said:
If you want simple FM transmitter try this one:

The values are for the 50us equalization used in Europe, Australia and New Zealand.

what is the mean of this, please explain it simply..
thanks..
 

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Re: Simple & Powerful FM Transmitter(only one transistor

ajex said:
zlatkoMM said:
how make L2 coil? can we use IF ferrite core (in FM radio)for making this coil.
The IF transformers in FM radios have a ferrite core and work at only 10.7MHz.
But the tuning coils in FM radios have air cores so that they can work at 100MHz.

can you tell me what is the distance that we can use to transmit.[/b]
These simple circuits do not have much power. FM radios have a wide selection of quality from cheap ones that might pickup a simple FM transmitter across the street to hi-fi and car radios that are extremely sensitive and can pickup a simple FM transmitter that is 2km (nothing in between) away.
My fairly low power FM transmitter has a range over a huge river valley of 2km.


"The values are for the 50us equalization used in Europe, Australia and New Zealand."

what is the mean of this, please explain it simply..
thanks..
America started broadcasting FM first. They boost the high audio frequencies (pre-emphasis) then the radio cuts the high audio frequencies (de-emphasis) so that the audio is perfect but hiss from the radio transmission is reduced. It is 75us.
It was a very long time ago when the high audio frequencies were fairly low level because microphones and recorders were poor.

Europe began broacasting FM later when microphones and recorders were better and they discovered that high audio frequencies were boosted too much by the Americans so they reduced the amount of boost to 50us. Australia and new Zealand made the same change as Europe.

So American and European radios have different EQs. But many simple FM transmitter circuits do not have any pre-emphasis so the de-emphasis circuit is all FM radios causes their sound to be muffled.
 

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If the transmitter had 200 mW RF power, it would take more than 35 mA and exceed BF199 Icm of 25 mA. Seriously, 50 to 100 mW can be expected.

Unfortunately, it has no output filter and will produce harmonics up to the UHF band.

P.S.: PSPICE says, it has about 95 mW at 300 ohm load, but only 30 mW at 50 ohm. Harmonics are around -20 dBc.:cry:
Supply current is about 40 mA and Q2 peak current around 50 mA.
 

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Re: Simple & Powerful FM Transmitter(only one transistor

how make L2 coil? can we use IF ferrite core (in FM radio)for making this coil.

The IF transformers in FM radios have a ferrite core and work at only 10.7MHz.
But the tuning coils in FM radios have air cores so that they can work at 100MHz.

No here telling to make it with ferrite core with one turns.. confused..!
 

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There are hundreds of FM transmitter projects on the internet. All of them use RF coils that have air cores. Just 5 turns to 9 turns is all they are.

Why do you want to be different and then maybe your circuit won't work?
 

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Re: Simple & Powerful FM Transmitter(only one transistor

Audioguru said:
There are hundreds of FM transmitter projects on the internet. All of them use RF coils that have air cores. Just 5 turns to 9 turns is all they are.

Why do you want to be different and then maybe your circuit won't work?

I tried to bulid above transmitter with air coil and with small ferrite road, but it doesnt work, I didn't use PCB for build it(used veroboard) is it happen to not working..? should I use a PCB for this circuit..?
 

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Re: Simple & Powerful FM Transmitter(only one transistor

I built my FM transmitter on a compact Veroboard layout with air-core coils and it works perfectly. Yours won't work if L1 has a ferrite core. Only the RF choke L2 uses a ferrite core.
 

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ajex

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Re: Simple & Powerful FM Transmitter(only one transistor

Audioguru said:
I built my FM transmitter on a compact Veroboard layout with air-core coils and it works perfectly. Yours won't work if L1 has a ferrite core. Only the RF choke L2 uses a ferrite core.

wow nice one, I want buil it soon, Audioguru I have a question with this, y u didn't use regulated supply for output stage..?? have special reason for that??
 

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The low-dropout 5V regulator (I= 9V input and O= 5V output) powers the oscillator to prevent its frequency from changing as the battery runs down, and powers the preamp so that its biasing doesn't change as the battery runs down.
The low-dropout regulator works perfectly until the battery drops to less than 5.5V. An ordinary 7805 or 78L05 fails when its voltage drops to less than 7V and a 9V battery quickly drops to less.

The output needs all the voltage it can get for good range. It transmits farther than 2km across a big river valley to my very sensitive home stereo and to my very sensitive car radio, 300m to my cheap Sony walkman radio and across the street to a clock radio or a cheap radio from The Dollar Store.
 
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zlatkoMM

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Re: Simple & Powerful FM Transmitter(only one transistor

First of all TX200 is not my design i just found schema on internet.
And i dont know how powerfull is it?
But one thing is interesting.
Look carefully how is designed oscilator part!
One advantage of using TX200 instead Audioguru design is better oscilator.
This way enable much stable output frequency deviation then Audioguru
design( im not 100% sure).
Then design of TX200 is much simple then AudioG design.
First coil is like says in text 3.5 turn on 5mm diameter air core coil.
Ferit stick with 5 mm you can use to adjust frequency of oscilator.
L2 is just ferit RF choke.

Added after 6 minutes:

2) Remove R2 and C4.
3) Change C5 to 330pF.
Dont remove C4 - use better 470pF
Change C5 to 10nF[/quote]
 

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Re: Simple & Powerful FM Transmitter(only one transistor

zlatkoMM said:
Look carefully how is designed oscilator part!
One advantage of using TX200 instead Audioguru design is better oscilator.
This way enable much stable output frequency deviation then Audioguru
design( im not 100% sure).
It has exactly the same oscillator circuit as mine. Except it has an emitter bypass capacitor. It is also modulated exactly the same as mine producing AM and FM.

Then design of TX200 is much simple then AudioG design.
But it sounds bad because its pre-emphasis (treble frequencies boost) is cancelled by the lowpass filter of R2, C4 and C5.
Since its RF amplifier is not tuned then its output will be full of harmonics which cause TV and communications interference.

Dont remove C4 - use better 470pF
The base of the transistor needs a small capacitance to ground so that the oscillator works as a common-base circuit. C5 couples the base to ground. C4 is not needed.

Change C5 to 10nF
Then all the high audio frequencies will be gone.
The high frequencies are supposed to have pre-emphasis provided by R1 and C2. A 330pf capacitor has a reactance of only 4.9 ohms at 100MHz and is fine to couple the base of the oscillator transistor to ground. 10nF is much too high.
 

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By using a LC tank, Audioguru's design has can be expected to generate less harmonics.
But a pirate radio doesn't care for regulations anyway.
 

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Re: Simple & Powerful FM Transmitter(only one transistor

Thanks for all who helped me to improve my knowledge. :D sometimes can't understand what you telling, but I got lots of experience in this Thread.. thanks very much for all....
 

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Re: Simple & Powerful FM Transmitter(only one transistor

Hi ajex
From where did you find the transistor. Im from Sri lanka too.
 

ajex

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Re: Simple & Powerful FM Transmitter(only one transistor

nalinda.com said:
Hi ajex
From where did you find the transistor. Im from Sri lanka too.

hello machan..
I got it from Ruwanwella citylight recordbar in 2yrs ago. you can buy it anywhere coz it is a very common transistor. also you can use 2N3553 or BFY50 transistor.

if you near to colombo you can buy it here > Unitec trading, 1st cross street. tel- 0114736590

if you near to maharagama check it here >> Kelum Electronics,highLevel Road,Maharagama. tel - 0112843102
 

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Re: Simple & Powerful FM Transmitter(only one transistor

Hello,
Thanks, it is a very common circuit, can be improved to make the freq stable and cut harmonics.
But the prob is you cant get quality devices in sri lanka. for an example you can get 2n3553 for 50 rupees but the qulaity is bad, it cant match the performance of original authentic manufacturer's that are expensive. even some cans are corroded, i dont know from where these 1st cross street people are getting those.
Thanks..
 

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Re: Simple & Powerful FM Transmitter(only one transistor

You can build this very frequency stable FM transmiter:
 

    ajex

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ajex

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Re: Simple & Powerful FM Transmitter(only one transistor

zlatkoMM said:
You can build this very frequency stable FM transmiter:
thz vry much.. :D
 

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