# Need a working long range FM Transmitter circuit

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#### bertus

Joined Apr 5, 2008
21,361
Hello,

As you might have noticed there are some HAM radio amateurs on this forum.

Bertus

Joined Feb 20, 2016
3,835
Just out of interest, many years ago, a couple of friends on mine built a radio transmitter just above the AM broadcast band. It was "safe" as no one used that space. But unfortunately for them, a harmonic fell spot on the local fire brigade frequency. As they were just teenagers, they got off pretty lightly when the authorities came calling. But they lost all their electronic equipment, radios, test gear, tape recorders.....
And they had a mark against their names.

#### recklessrog

Joined May 23, 2013
985
The point of what you seem to regard as negative responses is not that at all. There is no desire by anyone on here to stifle your learning and enjoyment of a wonderful hobby and career, but rather to offer advice as to do things in a proper manner. The way you describe going about it is akin to someone with an interest in firearms who thinks that "well I'm not going to shoot anyone if I do it out in the countryside", problem there would be, you have no control over the projectile once fired, or the public wandering into the line of fire. That may be an extreme example, but is in line with your proposal. You could cause interference to some critical communication without knowing. THAT is why there are rules and regulations to prevent that. Also, you need to show competence in making sure what you are transmitting is within the legal boundaries.
As a licenced amateur radio operator, I would encourage you to study the subject, get a licence, then experiment within the terms of the licence.
(better than getting caught, fined, and having your equipment confiscated)

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#### Audioguru

Joined Dec 20, 2007
11,249
Sribasu,
Do you know what a sine wave is and what it looks like? It is a single pure frequency with no harmonics. I simulated your very simple circuit and its output is not a pure sine wave because it is full of harmonics. The harmonics will occur on multiples of the 75MHz frequency you selected.

Do you know the spec called "capture ratio" for an FM radio? It is the small ratio of signal strength difference for one transmission to "capture" another signal that is on the same frequency or one of your many harmonic frequencies. It completely jams the other signal. AM transmitters do not do this, they cause interference where both transmissions can be heard at the same time which is why airplane communications use AM not FM.

You said you will transmit MP3 audio. But your transmitter is so simple it does not have pre-emphasis that is used by all FM radio stations and is cancelled by the de-emphasis used in all FM radios. Yours will sound muffled with no high audio frequencies.

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#### Alec_t

Joined Sep 17, 2013
12,060
Transmitting MP3 audio is likely to require a licence to stay legal. There are copyright issues to consider.

#### Janis59

Joined Aug 21, 2017
1,332
RE:""I am looking for a 10 KM range""
1) The typical 25 Watt 27 MHz vehicle system works well between 10-20 km. Compare the 0,1W of Your proposed circuit with 25W! Your circuit will provide a maximum 100 or 200 meters.
2) Only low-power solution is LPWAN like Nordic up to 1 km (https://www.nordicsemi.com/eng/Products/2.4GHz-RF/nRF2402)and LORA up to 3 km (CSS modulated), see www.link-labs.com/blog/what-is-lora. Actually I checked LORA on 3rd floor in middle of high city and receiver on walking man, what gave those 3km. Probably with slightly boosted power and higher antennas the 10km are not a just dream.

Thus, I recommend OR to buy the standard radio (I bought one last week so cheap as 15 USD) or LORA and master on that the simple booster amplifier.

Read the article here in entrance page section industrry articles about Digital Zig Bee 3.0 RF (https://www.digi.com/products/models/xb3-24z8rm). It gives a 3 km by even a microscopic antenna, thus You may which over antenna there to triple the distance.

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#### Janis59

Joined Aug 21, 2017
1,332
RE:""I understand it transmits to every direction. Can a unidirectional Antenna prevent it?""
Of course.
1) Antennas having rather narrow peaks symmetrically around vertical axis. For example, quadrat, double quadrat, tripple quadrat
2) Antennas having very narrow main lobe and few very weak back and side lobes. For example, Yagi-Uda, LogoYagi etc.
3) Antennas having round diagram around the azimuth, but having very narrow lobe about altitude. There one may look for zero fild straight up (as we have no aim to irradiate the stars) but very strong horisontal component. Such is Sli-Jim as well the slopy ground quadrat.
4) And at last antennas what are just nothing worth, but simple and cheap, namely the 1/4 wave vertical vibrator, 1/2 wave horizontal vibrator, 1/10 wave CLC antenna, changing step spirall antenna so popular at 27 MHz vehicles, naked coaxial cabling with 1/4 Wave braid got rid etc, duck-necks etc.

#### BR-549

Joined Sep 22, 2013
4,938
sribasu......sorry to bust your bubble. But you have NOT built a transmitter.......you have built an oscillator with a wire attached to it. It only demonstrates the radio principle.

You may pick it up on a close by receiver only. You will need to study many more circuits and then study antennas and wave propagation.

For 10km....one doesn't need much power....with the right frequency and antenna.

#### sribasu

Joined May 10, 2017
18
I've probably understood what you all meant, in summary.
I'll go through the Books and try to learn it the right way. May be consider applying for a HAM Operator License if I really want to make a really powerful transmitter and use it. Special thanks to @bertus you've shared some invaluable links!!

#### dante_clericuzzio

Joined Mar 28, 2016
229
There are some people on who done 5 KM they said but i am not convince for sure...but for 10 KM maybe you have to ask the expert who doing the radio antenna that can transmit up to 100 km

#### Janis59

Joined Aug 21, 2017
1,332
The typical 5 mW transmitter on 2400 MHz takes some 20-30 meters afar.
The typical 200 mW transmitter on 27 MHz takes 250 meter afar
The typical 5 Watt 160 MHz sailor station takes about 1-2 km away.
The typical 25 Watt 27 MHz trucker radio takes 10-15 km away.
The Polish Warszawa Vtura (Lato z radiem) at 1980 has 100 Megawatt power at Long Wawes, and about 1000 km was the effect.
However the Transworldradio 1 kW station from Equador is possible to hear in precise contrary side of planet, Europe at Riga city (sad their program is blablabla). Therefore theoretically, with extra good stationary antenna and right 25 m wavelength one may get trouble over the whole Planet with some 10 Watts. Thus, the length has a meaning here, not only muscles`.

#### Janis59

Joined Aug 21, 2017
1,332
RE:""May be consider applying for a HAM Operator License if I really want to make a really powerful transmitter and use it""
You ought to choose do You want to be a designer or user. Both together its rare wonder.
Hopefully You know that old anecdote about chukcha writer coming to his book opening celebration, where they ask him to read something but realize that he haven’t be learned how to read. But chukcha is bravely explaining - I am not the Reader, I am Writer.
The same way, the amateur radio - means sport of how to get the most far calls in most short time, the ham radio means to create own news releases and bad music and to hope that inspectorate will not catch You but listeners will like those garage music. And designers construct the better and better boxes full of components tho those first two and everyone is happy. The problem starts if the equilibrium is shaken....

#### GopherT

Joined Nov 23, 2012
8,012
How is it tha everyone here is so concerned that this guy, half way around the world, breaks an andministative law an you write paragraphs and paragraphs about why he shouldn't do it.

Were you guys the ones telling the high school teacher that Jimmy is having a beer party, or Johnny has a bag of hash? Or, are you the type that lets your brother-in-law drive home while he was all tuned up but have to lecture @sribasu about possibly interfering with FM radio reception in Hyderabad?

Joined Feb 20, 2016
3,835
How is it tha everyone here is so concerned that this guy, half way around the world, breaks an andministative law an you write paragraphs and paragraphs about why he shouldn't do it.

Were you guys the ones telling the high school teacher that Jimmy is having a beer party, or Johnny has a bag of hash? Or, are you the type that lets your brother-in-law drive home while he was all tuned up but have to lecture @sribasu about possibly interfering with FM radio reception in Hyderabad?
No, we are the ones that say to Jimmy, "Don't have that beer party", Johnny, "get rid of your bag of hash" and brother-inlaw, "Don't you dare drive home all tuned up. Have more respect for my sister and yourself!"

And why do we care about some body on the other side of the world? Well, some of us do have a world view.

#### nsaspook

Joined Aug 27, 2009
8,375
How is it tha everyone here is so concerned that this guy, half way around the world, breaks an andministative law an you write paragraphs and paragraphs about why he shouldn't do it.

Were you guys the ones telling the high school teacher that Jimmy is having a beer party, or Johnny has a bag of hash? Or, are you the type that lets your brother-in-law drive home while he was all tuned up but have to lecture @sribasu about possibly interfering with FM radio reception in Hyderabad?
Because radio interference from a illegal and most likely unstable transmitter can get people far away and unknown to the radio bandit injured or killed by interfering with emergency services.

#### Audioguru

Joined Dec 20, 2007
11,249
Maybe over there they have no emergency services, or maybe nobody cares if there is interference..

#### GopherT

Joined Nov 23, 2012
8,012
Because radio interference from a illegal and most likely unstable transmitter can get people far away and unknown to the radio bandit injured or killed by interfering with emergency services.
If that is your argument, you are essentially confirming that you haven't spent much time in India.

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#### nsaspook

Joined Aug 27, 2009
8,375
If that is your argument, you are essentially confirming that you haven't spent much in India.
You can do better.

#### DickCappels

Joined Aug 21, 2008
7,417