5km fm transmitter

Ziddik · Jul 13, 2011

Hi ppl

i got a simple fm transmitter circuit from net says it can transmit signals upto 5km of range using a single 2sc1162 transistor but the transistor is not for VHF circuits! So guys is it possible using this transistor? I got a pic of the circuit and have posted it, thanx

ronsimpson · Jul 13, 2011

5km....no...maybe with a 5km antenna.

crutschow · Jul 13, 2011

Remove the k from km and you'd be much closer to reality.

colin55 · Jul 13, 2011

Use a 2N2219A or something similar

audioguru · Jul 13, 2011

The Japanese transistor is a power type that works up to 180MHz, its supply is 12V and its emitter resistor value is low so it will have a fairly high output power. It might be detected by a very sensitive radio at 5km. It is illegal because it might cause interference.
The extremely simple circuit has the antenna connected directly to the tuned circuit so the variable capacitance of something moving toward or away from the antenna will change the frequency.
The circuit does not have a voltage regulator so if it is battery powered then its frequency will change as the battery voltage runs down.
It is missing pre-emphasis (treble boost) so it will sound awfully muffled on an FM radio (they all have de-emphasis).

Ziddik · Jul 13, 2011

thanx audioguru, u r the best expert in electro, anyway i got two 2sc1162 in my junk box so i am gonna try it if it doesn't work i am gonna kick the moron's *** so hard! (the one who designed it)

thanx for replay audioguru

Ziddik · Jul 13, 2011

heya ronsimpson, can u pls send me a 5Km bipolar antenna? I appreciate ur replay lol..

Ziddik · Jul 13, 2011

hi audioguru,

is treble boosting possible using a ceramic capacitor? I have seen something on circuits using a 333nf ceramic cap

colin55 · Jul 13, 2011

You need a transistor with a high FT (max frequency) to work in this type of stage. (180MHz is quite useless)

Ziddik · Jul 13, 2011

why do i need 180Mhz then! **broken link removed** i want 88-108 mhz **broken link removed**

colin55 · Jul 13, 2011

You need about 300MHz.
The reason is this:
At 180MHz, the transistor has a gain of 1 That's how they work out the maximum frequency for the device.
To get 100mW out of the device you will have to deliver 100mW into the base.
This is not what you want to do.
You want a gain of at least 30.
You want a transistor with a cut-off frequency of about 300MHz so that as you come down the graph to 100MHz, it will have a gain of about 30.
A 180MHz transistor will only have a gain of about 5-10 at 100MHz. That’s why you need a high FT transistor.

Ziddik · Jul 13, 2011

thanx colin **broken link removed** so what kinds of transistors should i use instead of that 2sc1162?

Ziddik · Jul 14, 2011

audioguru said:
The Japanese transistor is a power type that works up to 180MHz, its supply is 12V and its emitter resistor value is low so it will have a fairly high output power. It might be detected by a very sensitive radio at 5km. It is illegal because it might cause interference.
The extremely simple circuit has the antenna connected directly to the tuned circuit so the variable capacitance of something moving toward or away from the antenna will change the frequency.
The circuit does not have a voltage regulator so if it is battery powered then its frequency will change as the battery voltage runs down.
It is missing pre-emphasis (treble boost) so it will sound awfully muffled on an FM radio (they all have de-emphasis).

i built the circuit but it doesn't work! I replaced The 3.3 ceramic capacitor with a 472, is that the problem? In which frequency it would transmit signals? I got a 87-108 mhz fm radio, and what will be the written value of a 3.3 pf ceramic capacitor(333?)? Btw i have a 2n3886 transistor in my junk box! Is there Any 2km or 1km fm transmitter circuits using it? **broken link removed** .

Ian Rogers · Jul 14, 2011

Picture's a bit OTT...

colin55 · Jul 14, 2011

3p3 is two pieces of enamelled wire 5cm long twisted together. or 2x 10p in series

colin55 · Jul 14, 2011

When you said 5km transmitter, I thought the stage was a linear amplifier.
It's an 88MHz oscillator.
Use any 2n2222 transistor and get the circuit to work with 47k base and 470R emitter resistors. Remove the other resistor. Use the Field Strenght Meter on Talking Electronics website (Under Voyager) to detect an output and then try to increase the output.
It's very difficult getting power transistors to work in this stage (practically impossible).

Ziddik · Jul 14, 2011

colin55 said:
When you said 5km transmitter, I thought the stage was a linear amplifier.
It's an 88MHz oscillator.
Use any 2n2222 transistor and get the circuit to work with 47k base and 470R emitter resistors. Remove the other resistor
It's very difficult getting power transistors to work in this stage (practically impossible).

i have already built a transmitter usin 2xBC547 for connect to my TV so i can watch tv even at midnight without disturbing anyone lol i mean i have a radio on my mobile so i can listen the transmitted voice through my headphone! Hows my idea! Feels like a movie theatre while watching a movie through my headphone! And now i want make another transmitter to cover more range, u said 'increase output' how could i do it? Can u explain it pls?

audioguru · Jul 14, 2011

A "typical" 2SC1162 transistor will oscillate at the frequency of FM radio stations. A few don't.
You need a circuit to boost high audio frequencies (pre-emphasis) which includes a capacitor but I use a metalized plastic film capacitor, not ceramic.

Ziddik · Jul 16, 2011

audioguru said:
A "typical" 2SC1162 transistor will oscillate at the frequency of FM radio stations. A few don't.
You need a circuit to boost high audio frequencies (pre-emphasis) which includes a capacitor but I use a metalized plastic film capacitor, not ceramic.

how about 2n3866? :? Is there any circuits using it for a long range?

transistor495 · Jul 16, 2011

Ziddik said:
Hi ppl

i got a simple fm transmitter circuit from net says it can transmit signals upto 5km of range using a single 2sc1162 transistor

Please post a link to this article

5km fm transmitter

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