another FM transmitter project

Ziddik · Jul 22, 2011

How can RF cops find you? Is there any special tool for it like Tracker transmitter?

audioguru · Jul 22, 2011

Ziddik said:
How can RF cops find you? Is there any special tool for it like Tracker transmitter?

I got caught by the RF cops when I was a teenager in my first apartment. I made a fan from an old electric motor and the propeller from a large model airplane. The motor sparked badly and caused interference to hundreds of radios and TVs. The RF cops were very nice but took away my fan. The neighbours who complained bought a new fan for me.

On one of these websites another guy near me made my FM transmitter then he saw the RF cops driving down his street in their van with the rotating antenna on top. Maybe they were looking for me?

Ziddik · Jul 22, 2011

oh man, **broken link removed** ur fm transmitter must be powerful then lol and there are only 2 active radio stations
at my area becauz i am so far away from overcrowded towns and apartments and my house stays in the middle of a very vast place surrounded by rivers and large trees thus i think i can use a powerful transmitter, moreover there are no RF cops or Rf offices here so i dont have any troubles for using a transmitter, btw can i replace the last 2n3904 transistor of ur circuit using 2n3866? what kinds of modifications will i need on the circuit to replace it? (guess.. the value of base ressitor?)

audioguru · Jul 22, 2011

I have about 30 very strong local FM stations and about 20 that are all around me a little farther away in surrounding cities. It is difficult to find a vacant frequency. Since you live on Mars then there will not be much interference.

If you change the output transistor then the new transistor must be properly biased so it works the same as my 2N3904 transistor. If you want a stronger output then the new transistor will need a stronger input maybe from an additional driver transistor.

Ziddik · Jul 22, 2011

hi audioguru

i powered ur transmitter circuit using a 3.7v mobilephone battery so how much k-ohm can be the value of biasing resistor of 2n3866? A nokia 3.7v battery has high current so it will work perfectly

Ziddik · Jul 22, 2011

30 radio stations on a 87-108mhz radio must be an annoyance and trouble to ur RF related works.. I would interfere all those stations if i was there in canada **broken link removed**

audioguru · Jul 22, 2011

Ziddik said:
hi audioguru

i powered ur transmitter circuit using a 3.7v mobilephone battery so how much k-ohm can be the value of biasing resistor of 2n3866? A nokia 3.7v battery has high current so it will work perfectly

You don't understand that most transistors have the same voltage gain. The old 2N3866 is in an old metal case so a clipped-on heatsink can keep it cool. Since it has the same voltage gain as a tiny 2N3904 transistor then for more output power its needs more input power. It needs a driver transistor to provide it with more input power.

My transmitter uses a 9V battery. If only 3.7V is used then its output power is very low. It would need a re-design to work properly with a supply of only 3.7V.

Nepaliman · Mar 24, 2012

audioguru said:
My FM transmitter is fairly low power so a BC547 will work the same as my 2N3904.

"How many long it could be reach" does not make sense in English. Maybe you are asking how far away it can be received which we call "its range"?

I tested it across a large river valley with nothing in between. It was more than 2km to my expensive very sensitive FM stereo and my very sensitive car radio, it was about 300m to a cheap portable Sony Walkman FM stereo radio and it was across the street to a cheap FM radio from The Dollar Store (it uses a TDA7088 FM radio IC). The Dollar Store sells very cheap Chinese and Indian junk). In my neighbourhood houses and trees reduced the range a lot.

The transmitter antenna was 80cm long and hanged vertically out an upstairs window. My FM stereo and car radio antennas were also long and arranged vertically. My Sony Walkman radio uses its earphones cord as the antenna (not good) and the radio from The Dollar Store has a whip antenna that is much too short at about only 12cm (it picks up only strong local stations but is also overloaded by many of them).

Many cheap FM radios are overloaded by strong local stations so the range will be reduced a lot. My cheap Sony Walkman radio has a local-distant switch that attenuates the antenna input when switched to local. When overloaded a station appears at many points across the dial.
When my transmitter is close to a cheap radio then it appears at many points across the entire dial.

Guru, which is that circuit? Plz show me or give me URL plz

audioguru · Mar 24, 2012

This is my FM transmitter circuit. I built it on stripboard and I cut the strips with a drill bit. The strips form half of a pcb.

Nepaliman · Mar 26, 2012

audioguru said:
This is my FM transmitter circuit. I built it on stripboard and I cut the strips with a drill bit. The strips form half of a pcb.

Dear guru,
Is L1 and L2 by 10 turn of 1mm wire on 3mm former in your this FM? Is 1mm means 20 SWG?
There are some question, trying to know from a year, please...guru:
1) Oscillator and RF amplifier separated circuit (like your) gives more RF power and long range too?
2) Is it possible to make different another RF buffer stage using 3904 for great range? Please guru, design or show me a circuit like this.
3) I heard that S8050 gives more RF output power better than 3904, is it true?

Thank you a lot.

audioguru · Mar 26, 2012

Nepaliman said:
Dear guru,
Is L1 and L2 by 10 turn of 1mm wire on 3mm former in your this FM? Is 1mm means 20 SWG?

1mm wire is thick. It might be 14SWG. They have 9 turns. It has enamel insulation.

1) Oscillator and RF amplifier separated circuit (like your) gives more RF power and long range too?

The RF amplifier separates the oscillator from the antenna so things moving toward and away from the antenna do not change the oscillator's frequency.
The RF amplifier has plenty of power for a distant range.

2) Is it possible to make different another RF buffer stage using 3904 for great range? Please guru, design or show me a circuit like this.

A buffer will not work unless the supply voltage is increased and a higher power RF amplifier transistor is used.

3) I heard that S8050 gives more RF output power better than 3904, is it true?

The Chinese datasheets give no spec's for use at VHF radio frequencies.
Weitron in Taiwan make an S8050 NPN transistor. Wing Shing in China make an S8050 PNP transistor. Which one is correct?

Nepaliman · Mar 26, 2012

I've built a Fm transmitter using single transistor bf494. If i powered it with 12v, 45 amp. battery, will my transmitter damage due to high ampere or not?? Thus, a instruement which can be operated at 12 voltage at low ampere, but if i connect this instruement with any 12 voltage high ampere battery, WHAT WILL BE???

Nepaliman · Mar 27, 2012

audioguru said:
The Chinese datasheets give no spec's for use at VHF radio frequencies.
Weitron in Taiwan make an S8050 NPN transistor. Wing Shing in China make an S8050 PNP transistor. Which one is correct?

I think that is s8050 is NPN. Please check this FM transmitter circuit of s8050
https://ziddique.wordpress.com/2011/12/28/simplest-fm-transmitter/

Can it transmit more than 1km? Is it reliable circuit? Please check the circuit and tell me true please! Is both s8050 PNP and NPN in same size? How to know which is NPN?

audioguru · Mar 27, 2012

Nepaliman said:
I think that is s8050 is NPN. Please check this FM transmitter circuit of s8050
https://ziddique.wordpress.com/2011/12/28/simplest-fm-transmitter/

Can it transmit more than 1km? Is it reliable circuit? Please check the circuit and tell me true please! Is both s8050 PNP and NPN in same size? How to know which is NPN?

Use a S8050 NPN transistor made by Weitron of Taiwan. I think Wing Shing of China has a translation problem with their datasheet.
Both transistors look the same.

It is easy to use a multimeter diode test see if an emitter-base or collector-base is NP or PN.

Ziddik is a member of this website or another electronics chat site.
His notes say its range is 1km when powered from 12V, not 3V. I have never seen a Chinese S8050 transistor.
He doesn't say the sensitivity of his FM radio but it must be very high. A cheap poor quality FM radio might receive the signal across the street or in the next room.

It is SIMPLE so it is not reliable:
1) Its antenna connects directly to the tuned LC of the oscillator so its frequency changes when something moves toward or away from the antenna.
2) It does not have a voltage regulator so its frequency changes as the battery voltage runs down.
3) It sounds awful with no high audio frequencies. Like an AM radio, a telephone or your stereo with its treble tone control turned all the way down.
4) It is mono, not stereo.
5) It might cause interference with FM radio stations, police, ambulance, aircraft communications and guidance or TV. Then you will have BIG trouble from the RF cops. They might chop your head off or shoot you or both.

On Ziddik's website he shows a photo of a Canakit R171 FM transmitter kit that is not available anymore. It might have been the same simple lousy circuit as his.

Nepaliman · Mar 27, 2012

audioguru said:
This is my FM transmitter circuit. I built it on stripboard and I cut the strips with a drill bit. The strips form half of a pcb.

i an going to build this, so make of clear please.
1) in your circuit diagram, there are 3 transistor but in real built transmitter figure, there are 4 transistors and other additional devices. What is that? Which is this another one transistor?
2) tell me exactely how much gauge in 1mm?
3) are L1 and L2 in 3 mm former?
4) Can i wind aluminium insulated wire instead of copper wire?
5) How to wind coil correctly? When i wind coil, it stretches immediately.

Nepaliman · Mar 27, 2012

audioguru said:
This is my FM transmitter circuit. I built it on stripboard and I cut the strips with a drill bit. The strips form half of a pcb.

i am going to build this, so make me clear please.
1) in your circuit diagram, there are 3 transistor but in real built transmitter figure, there are 4 transistors and other additional devices. What is that? Which is this another one transistor?
2) tell me exactely how much gauge in 1mm?
3) are L1 and L2 in 3 mm former?
4) Can i wind aluminium insulated wire instead of copper wire?
5) How to wind coil correctly? When i wind coil, it stretches immediately.

audioguru · Mar 28, 2012

Nepaliman said:
1) in your circuit diagram, there are 3 transistor but in real built transmitter figure, there are 4 transistors and other additional devices. What is that? Which is this another one transistor?

It is the LM2931A 5.0 which is a 5V low-dropout voltage regulator in the same small plastic case as the transistors. There are many 5V low-dropout voltage regulators available today.

[/quote]2) tell me exactely how much gauge in 1mm?[/quote]
Look in Google.

3) are L1 and L2 in 3 mm former?

I wound them on a 3mm diameter drill bit.

4) Can i wind aluminium insulated wire instead of copper wire?

Can you solder to aluminum? I can't.
I used short pieces of thick copper enamelled wire from the crossover coil in a speaker enclosure. It had lots of this wire.

5) How to wind coil correctly? When i wind coil, it stretches immediately.

My wire is solid copper wire that is stiff and stays coiled. Maybe you are using stranded wire that is flexible.

Nepaliman · Mar 29, 2012

ASKING TO YOU AGAIN:
I've built a Fm transmitter
using single transistor
bf494. If i powered it with
12v, 45 amp. battery, will
my transmitter damage
due to high ampere or
not?? Thus, a instruement
which can be operated at
12 voltage at low ampere,
but if i connect this
instruement with any 12
voltage high ampere
battery, WHAT WILL BE???

audioguru · Mar 30, 2012

Nepaliman said:
ASKING TO YOU AGAIN:
I've built a Fm transmitter
using single transistor
bf494. If i powered it with
12v, 45 amp. battery, will
my transmitter damage
due to high ampere or
not??

You did not post your detailed schematic so we cannot calculate its maximum collector current.
Didn't you see its maximum allowed collector current on its datasheet?
Didn't you see its maximum allowed heating?
Can't you calculate yours?

Nepaliman · Apr 3, 2012

If so, may i supply from 12 v, 45 amp. large battery to your 3904's transmitter? I have no idea to do such equation.

another FM transmitter project

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