1w fm transmitter

[azrocat]

i have this transmitter assembled and tested.
i wonder, can i remove microphone and add audio input (mp3 payer) (mono) and if yes, where can i connect it?

[titi]

Hello azrocat,

Just connect you MP3 cable shield to point 5 and MP3 signal on point 6 (at the place of the microphone).

VR1 to adjust the injected signal to not saturate the transmitter.

Best regards.

[dennis78]

This isn't 1W transmitter. Maybe 1mW.  Also, this is more am than fm trasmitter, but it works.

[pickit2]

http://www.communica.co.za/Catalog/Details/P0153863043

1W

[micropcb]

Here is another one based on a project in  the magazine Electronics for You.

http://www.electroschematics.com/5594/four-stage-fm-transmitter/

EFY link

http://www.electronicsforu.com/electronicsforu/circuitarchives/view_article.asp?sno=67&article_type=1&id=464&tt=unhot


Cheers.

[dennis78]

http://www.communica.co.za/Catalog/Details/P0153863043

1W

Yes, but single-stage RF(very simple common-base RF oscillator) with 1W output power (+ RF transistor doesn't so good characteristics)... maybe but, I am very suspicious.

Here is another one based on a project in  the magazine Electronics for You.

http://www.electroschematics.com/5594/four-stage-fm-transmitter/

EFY link

http://www.electronicsforu.com/electronicsforu/circuitarchives/view_article.asp?sno=67&article_type=1&id=464&tt=unhot


Cheers.

This is more seriously circuit and I think it can be 1W or more.

[h0nk]

Hello azrocat,

You should take a look on e*ay for "Sony Ericsson MMR-70 FM Transmitter".

http://www.ebay.com/sch/MMR-70

They are based on an Atmels ATMEGA32 and an Alps-Module and reach in testmode approx. 10 mW.
But You must be able to reprogram the ATMEGA32 to use these.

They offer stereo capability and excellent frequency stability.


Best Regards

[kayvee]

Yes, but single-stage RF(very simple common-base RF oscillator) with 1W output power (+ RF transistor doesn't so good characteristics)... maybe but, I am very suspicious.

A little bit more (but not a whole lot) on the manufacturers website of the one pickit2 linked:

http://www.smartkit.de/aid-11-FM-Transmitter-1-Watt-A-simple-but-very-powerful-FM-transmitter.html

[Droneman1982]

1W single stage, apart being completely illegal it sounds very strange to achieve in a single stage. The power dissipation of the final stage (class A amp) would require good heatsinking and will operate only at low duty cycle....

[pickit2]

this was in the quasarelectronics catalogue after being printed in I think Everyday Practical Electronics, before being made illegal after the laws were changed, to outlaw such devices.
The original was hacked to over 2W back in the day.

[PM3295]

I ran a quick ADS Harmonic Balance simulation on the smart kit transmitter assuming operation at 9 V. The maximum RF out shows to be about 20 mW, which are a long way from the 1 W claimed. Running at 12 V produced only 39 mW.

[Vineyards]

This isn't 1W transmitter. Maybe 1mW.  Also, this is more am than fm trasmitter, but it works.

Why do you think so. As far as I can see, there is a modulator stage coupled to an L/C oscillator. The value of C1  determines the basic operational frequency but TR1 also has a small capacitance between its base and emitter. The capacitance between TR1's base and emitter depend on the voltage its base receives from the modulator stage which is an audio signal  hence the frequency of the oscillation changes based on the emitter current of TR1 due to the varying input on its b.

This design is a basic one because it uses a VCO (Voltage Controlled Oscillator) however there are no provisions for voltage fluctuations on the power supply. As the voltage goes up and down the frequency will shift drastically.

[PM3295]

power suply is up to 30 V

Simulation result at 30 V supply is 22.9 dBm (~200 mW). That is about what I expected to see.

[Droneman1982]

how much power dissipation in the output stage?

[chicane]

i connect audio source to mic point, but sound from receiver is fuzzy. (with mic it was perfect)

Might be your audio source's amplitude is too high for the circuit? clipping the signal can make audio sound fuzzy. Maybe try a differnent value for VR1? Always liked crystal controlled circuits, but hey this is simple circuit, if you can keep frequency drift within what you find acceptable for your purpose.

[2N5109]

It might work depending on how much poop your MP3 player puts out.  If not enough, try repeating the amplifier stage, R4, R5, C3, C5 and TR2.  Put it in cascade with the one already there.  Also make sure the audio MP3 leads are shielded, it can be high impedance point, will pick up magnetic field strays, causing fuzz.

--2N5109

[PeterMcMonty]

simple, but it works. Maybe it's not 1W but just 200 mW or so, who cares? After all, it is for educational purposes and the range sould be within tens or hundred of meters anyway.
It is illegal in most countries, but in practice its use perhaps may be tolerated in most of them (depends on the telecom authority controls.. ).

For sure http://www.electroschematics.com/5594/four-stage-fm-transmitter/ or http://www.electronicsforu.com/electronicsforu/circuitarchives/view_article.asp?sno=67&article_type=1&id=464&tt=unhot (they are the same) is more serious one, but you need some skill to trim all the stages for maximum output, where azrocat's one is much simpler (just one trimmer to set to max output at desired frequency).

About MP3 driving, I agreed with chicane: maybe too high amplitude... microphones gives a very low signal, while MP3 may be much higher.
Also 2N5109 advices makes sense, expecially when he warns about shielding audio MP3 leads to avoid picking up noise.

[marianqt]

I remember a few years ago, i built a simple oscillator with one transistor(2n2219). I was without much experience. No output low pass filter, no oscillator pll or crystal, so no stability, with a sort of WBFM modulation... the grid 50 hz from non well filtered power supply. Antenna was a wire of 50 cm. Results: A couple of kilometers of range. So i came back at home and i disconnect the transmitter. Fortunately no one came at my home door .

[2N5109]

Probably if you use 30v you could get 1 watt out at low end of band. Oscillator efficiency can be 20-30% so you need to put in 5 watts and need heat sink. The 2N2219 in TO5 can could do that. But you need better stability and controlled deviation (<100kHz) to be serious.

-2N5109