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To design a very powerful long range fm transmitter

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Mg Myo Ko

New Member
I am very interested in fm transmitter.But I have not enough knowledge to construct such a fm transmitter circuit on my own really .I have no chance to buy a fm transmitter from other countries around the world because my country has no "clear money exchange system " to take relationship with on-line stores.
I have constructed short range fm transmitters and I had successs on them
But I don't satisfy with their "range" .So I searched long range transmitter circuits on internet.But I can't find what I want so far.So Could someone help with this problem?.I want to design & construct a long range fm transmitter having the transmitting distance of up to five miles around .I would use that circuit to broadcast songs as an amateur .( My country has no "hard " limitations on transmitting ) I will use that transmitter at my "countryside".So who could give me a helpful hand with this my "big dream " crazy? .
Please.RFC coils are not allowed there in my circuit design because these RFC coils could not be bought any where in my country .
With . Thanks a million,
Mg Myo Ko
 
Last edited:

Papabravo

Well-Known Member
I am very interested in fm transmitter.But I have not enough knowledge to construct such a fm transmitter circuit on my own really .I have no chance to buy a fm transmitter from other countries around the world because my country has no "clear money exchange system " to take relationship with on-line stores.
I have constructed short range fm transmitters and I had successs on them
But I don't satisfy with their "range" .So I searched long range transmitter circuits on internet.But I can't find what I want so far.So Could someone help with this problem?.I want to design & construct a long range fm transmitter having the transmitting distance of up to five miles around .I would use that circuit to broadcast songs as an amateur .( My country has no "hard " limitations on transmitting ) I will use that transmitter at my "countryside".So who could give me a helpful hand with this my "big dream " crazy? .
Please.RFC coils are not allowed there in my circuit design because these RFC coils could not be bought any where in my country .
With . Thanks a million,
Mg Myo Ko
myokoko19@gmail.com

It is pretty hard to imagine an FM transmitter with a five mile range that does not use inductors. You might want to consider removing or disguising your email address in your post. The spambots will find it an pound your inbox relentlessly. What is your country by the way?
 
Last edited:

MikeMl

Well-Known Member
Most Helpful Member
Simply put, you cannot build a high power transmitter without LC tuned circuits. Coils are easy to construct; Capacitors rated for high-frequency RF currents are a tougher problem, but could be fabricated using parallel-plates and air dielectics.

To get the range you want, you will need a transmitter capable of producing ~1 to 10W of RF output presumably at ~100mHz. To get that you will need a tube and a high voltage power supply.

Can you scrounge some old tube-type TV sets?

See if you can get access to an 1960's or 1970's "The Radio Amateur's Handbook". It has all the basic circuits, oscillator, FM modulator, RF power amplifier, Power Supplies, and antennas. The older books had a lot of tube circuits which might be easier to duplicate from parts from a TV set compared to newer books with use specialized IC and solid-state parts which you will have a hard time obtaining.
 
Last edited:

RadioRon

Well-Known Member
I want to design & construct a long range fm transmitter having the transmitting distance of up to five miles around .I would use that circuit to broadcast songs as an amateur .( My country has no "hard " limitations on transmitting ) I will use that transmitter at my "countryside".So who could give me a helpful hand with this my "big dream " crazy? .
Please.RFC coils are not allowed there in my circuit design because these RFC coils could not be bought any where in my country .

If you cannot buy any parts it is difficult to give advice on a design. If it were possible for you to get the Rohm BH1414 integrated circuit, this would be an excellent starting point for your transmitter. This IC does all the hard work of generating a good carrier with stereo modulation. Here is the data sheet:
https://www.electro-tech-online.com/custompdfs/2009/10/bh1414k.pdf
In America, this part costs about $5US.

This IC will generate a very low level of power, so it will be necessary to add amplifiers to boost your power. It will probably be possible to find circuit schematics for simple amplifiers on the net, but again, you need to explain what parts you have access to.

You will need to use many RF inductors in your circuit, but you can make these easily yourself with solid copper wire.
 

EN0

Member
I would go towards the ICs. You can theoretically have four stages for your FM transmitter. This may include the audio amp, the oscillator, the modulator, and the power amplifier. Many ICs have both the oscillator and the modulator built together. If you want that kind of distance, I would advise you to build a very effective antenna. You shouldn't be overly concerned about size constraints, you might not be able to achieve something very small. Especially with the antenna.
 

ke5frf

New Member
In reality, the range of any radio transmitter isn't so much dependant on modulation type as much as frequency. There are optimal frequency bands between 160 meters and 6 meters which can transmit a great distance given ionospheric conditions and sunspots.

FM is typically not used in lower frequency radio because of the bandwidth requirements and the available "real estate".

In your case, it sounds like you want to use the accepted "commercial" frequencies for FM radio, for which recievers are commonplace. This would typically limit transmissions to Line-of-site and a measure beyond depending on terrain, amplifier power, and antenna height,construction. You would be amazed at how much you can do with very little power. I have QSL cards using CW (morse code) communication from clear around the world using less than 1 watt.

A few suggestions that might "help", assuming you can construct a maximized transmitter...

Antenna height. If you are in a mountainous area, that tiny transmitter might surprise you at elevation. If you are doing this for fun and not a permenant set-up, you may think of a portable radio station on a mountaintop. If you have the ability to weather-proof your equipment and have sufficient battery power, and a secret location, you might have fun doing it that way with an automated transmitter.

ANTENNA. You mention 5-miles *around*, and this would be a typical omnidirectional vertical antenna, but a resonant wire dipole will give you bidirectional coverage...if you aim at population centers you will achieve some gain (which is a misnomer in a way, but in other words you concentrate the transmission and reduce loss)

LOSS...important concept. Transmission lines intoduce loss with standing waves and resistance. The better your transmission line and all of your connections, and the shorter the line, the more use of your transmitting power that will not be wasted as heat.

If you have the inclination, a YAGI style antenna (think outdoor tv antenna) has maximized gain in a single direction. The reflector dipole elements help focus transmitter power. Multi-element yagis further do this. It is the equivelant of mirrors and lenses in an optical system, only with radio waves.

The antenna needs to be a full wavelength above ground, more if you can. Given a 10 meter antenna as an example, it will work optimally at 30+ feet above the ground.

Also, some evidence shows transmitting across saltwater helps with gain, though I doubt this will apply in what you are doing.

Some or none of this info might help you, but perhaps you did learn something new or someone else.

Oh one more thing...polarization. (Most) Any antenna style can be polarized vertically or horizontally, and with short range transmitters (for which even 5 mile radius includes) it is important that the recieving station be polarized the same way, It has been a while since I played with my radios and built antennas, but 10-100 dB of loss occurs with cross-polarization.

It might be educational and fun for you to refer to the radio amateur's antenna handbook and googling "radio antenna", "dipole", "yagi", etc to get construction ideas and formulas for your frequency specifics.

Remember, a resonant antenna is by definition a function of radio frequency. A dipole is 1/2 wavelength, with 1/4 for each element to be efficient. There are off-center and multi-wavelength designs as well that give differing patterns for the transmission, but it is very hard to beat the standard 1/2 wave dipole.

And for transmission line, if you have the ability to match the impedance of your transmitters amplifier properly, parallel ladder line is very good, low loss stuff and you can construct it yourself with copper wire and popcycle sticks.

It is IMPERATIVE though, for the sake of your transmitter amplifer, that the impedance of your antenna is matched to the output impedance of the power transistor. Matching networks can be built, and that is, unfortunatley, where RLC circuits are neccessary.

However, matching can be done with the dimensions of the ladderline as well, along with methods you can employ found all over the internet.

Bad consideration is that many of these projects require at a minimum an SWR meter or an antenna analyzer to tune them to resonance.
 
Last edited:

ke5frf

New Member
I had another thought for an example of how YAGI antennas work.

Think about antennas and radio waves in similar fashion to sound speakers and audio waves. First, speaker impedance has to match the output impedance of the amplifier circuit. Often this is done with an audio transformer. This is the practical equivalent of matching a resonant antenna to a transmitter.

Now, much like antenna gain and efficiency can be maximized, so can a speaker. Audiophiles have special design techniques for the enclosure in which quality speakers are mounted.

Speaker boxes are designed in such a way that back pressures produced by the flex and contraction of the speaker diaphragm (on the backside) are reflected and REINFORCE the forward emitting sound waves coming off the working side. Without an enclosure these reverse sound waves are OUT OF PHASE and create cancellation and thus attenuate the sound. WITH the enclosure, the reverse, reflected waves are put back in phase with the forward waves and the effect is apparent gain. In reality, there is no gain here but rather prevented loss through cancellation/attenuation.

So, if you can imagine the Yagi antenna, with a reflector element as well as driven elements...the reflector achieves the same goal by reinforcing radio waves in a certain direction by reflecting them in phase with the desired forward or focused radiation. Again, in reality there is no "gain" from doing this, but loss is drastically reduced from radiated power in unwanted directions.

If you thought to use a Yagi for your transmissions, you could overcome the limitations of a directional antenna by rotating it 360 degrees with an electric motor. To clarify, the rotation wouldn't be constant (transmission lines wouldn't hold up!!! haha), but could be changed at a whim within a limited range of motor rotation to prevent transmission lines from tangling and twisting.

I hope my descriptions are adequate here for understanding.
 

EN0

Member
Quite a mouthful KE5FRF,

I'm sure he'll appreciate all that information.

I forgot about the the fact of limiting RF output power and antenna constraints. If he did use HF, his desired distance could be aggrandized and surpass what he originally expected. However, he seems to be implying about the standard FM radio bands for broadcasting and I'm not sure if 5 miles could be achievable under the FCC conditions they enforce. Well, I guess he'll just have to get his amateur radio license, eh?;) Then he could use one of those mini QRP CW HF transceivers and go across the world like you have. With 1W it seems hard to believe, but you must have been at the top of the sunspot cycle; hopefully we'll get more soon. Sunspots would improve his distance range too.
 

ke5frf

New Member
Quite a mouthful KE5FRF,

I'm sure he'll appreciate all that information.

I forgot about the the fact of limiting RF output power and antenna constraints. If he did use HF, his desired distance could be aggrandized and surpass what he originally expected. However, he seems to be implying about the standard FM radio bands for broadcasting and I'm not sure if 5 miles could be achievable under the FCC conditions they enforce. Well, I guess he'll just have to get his amateur radio license, eh?;) Then he could use one of those mini QRP CW HF transceivers and go across the world like you have. With 1W it seems hard to believe, but you must have been at the top of the sunspot cycle; hopefully we'll get more soon. Sunspots would improve his distance range too.

HA! Yes, I tend to elaborate more than neccessary sometimes, but I prefer to be thorough.

I am not sure he has to worry about the FCC, sounds like he is in an Asian country where FCC has no jurisdiction. However, international treaty is what FCC rules are based upon so being careful is advised. We don't want to encourage rogue transmissions or frequency pirating. I would always encourage ANYONE to get an amateur's license, which most every country has allowances for.

The most important point I was trying to make, however, is that the Antenna is by far the most important part of an efficient radio system.

Interesting that you brought up the QRP radio. Yes, I have a homebrew QRP transmitter that puts out about 3 watts, but the output transistor gain can be adjusted to less than 1 watt. This is actually considered QRPp (small p indicates milliwatts)

Now, I am a wire antenna enthusiast, and use a dipole hung from a tree. The 20 meter band is fabulous 365 days a year, every year...even during low sunspots. Sometimes there is a radio blackout where even that band is weak, but it is the HF operator's go-to band and great for QRP.

My 20 meter antenna is no longer in service, but it was only about 20 feet in elevation, and I had to use a tuner to match it, which introduced heat loss. My antenna was terribly inefficient but worked. I am quite certain that less than a watt ever made it out the antenna!!! I was able to make impressive contacts on 20 and 40 meters with this antenna with the tuner, however. Mostly during CONTESTS, when big stations with high gain antennas caught my signal. (antenna gain works both ways TX/RX) So in reality, their stations were doing all the work haha. But it is FUN thinking my little night light-power radio could talk around the world!

But I have a better story yet. Once I was taking a long trip in the car, and for giggles I hooked my HF tuner to my TWO METER (144 Mhz) whip antenna. I was able to tune 20 meters!!! I hooked up the little QRP rig and set up my Bengali CW key and keyer in the car. I was driving through Tennessee and made a CW contact in MAINE on 20 meters. He barely heard me with his loop antenna, but he got my callsign and greeting. I can only imagine how inefficient my setup was. maybe 100 mW getting out at most? And half of that straight up in the air! A car isn't much of a counterpoise.

And none of this was at the peak of the cycle, in fact it was just about 3 years ago when the last cycle was waning!!!

Electronics is a fun hobby, but amateur radio incorporates everything fun about it and more.

I have faded out of the hobby since I remarried and had a new baby, but I plan on setting up an inconspicuos antenna in the attic or something and at least my QRP rig in a corner of the garage soon. I can't go long without using my code skills or I'll get so rusty.
 

Mg Myo Ko

New Member
Thanks for your reply !

It is pretty hard to imagine an FM transmitter with a five mile range that does not use inductors. You might want to consider removing or disguising your email address in your post. The spambots will find it an pound your inbox relentlessly. What is your country by the way?[/QUOTE


First of all,I want to say "thanks" Papabravo ,for your time.Most of them who reply my thread are considering that I don't want inductors included in my circuit .I don't really mean like that. What I do not really want is RFC component like VK200 tosk .Those are very rare in my country .
Dear Papabravo, I really appreciate your words suggesting not to add my e-mail address in my threads .Thanks for that again! My country is Myanmar.Have you ever been to my country ,Myanmar, before,Papabravo?Looking forward your incomming suggestions for my circuit design with great hope!!
Sincerely :)
Mg Myo Ko
 

Mg Myo Ko

New Member
Really Thanks!

If you cannot buy any parts it is difficult to give advice on a design. If it were possible for you to get the Rohm BH1414 integrated circuit, this would be an excellent starting point for your transmitter. This IC does all the hard work of generating a good carrier with stereo modulation. Here is the data sheet:
https://www.electro-tech-online.com/custompdfs/2009/10/bh1414k-1.pdf
In America, this part costs about $5US.

This IC will generate a very low level of power, so it will be necessary to add amplifiers to boost your power. It will probably be possible to find circuit schematics for simple amplifiers on the net, but again, you need to explain what parts you have access to.

You will need to use many RF inductors in your circuit, but you can make these easily yourself with solid copper wire.

Dear RadioRon, Thanks for your datasheet.I'll download it and learn it.I could get most of the parts that required to design a amplifier circuit and I'll try them and post the results as threads .Keeping me with your help in my design! Thanks for lifetime,RadioRon.
 

Mg Myo Ko

New Member
Simply put, you cannot build a high power transmitter without LC tuned circuits. Coils are easy to construct; Capacitors rated for high-frequency RF currents are a tougher problem, but could be fabricated using parallel-plates and air dielectics.

To get the range you want, you will need a transmitter capable of producing ~1 to 10W of RF output presumably at ~100mHz. To get that you will need a tube and a high voltage power supply.

Can you scrounge some old tube-type TV sets?

See if you can get access to an 1960's or 1970's "The Radio Amateur's Handbook". It has all the basic circuits, oscillator, FM modulator, RF power amplifier, Power Supplies, and antennas. The older books had a lot of tube circuits which might be easier to duplicate from parts from a TV set compared to newer books with use specialized IC and solid-state parts which you will have a hard time obtaining.
I will try the book you suggest ,MikeMI. I have said that I have very little knowledge about circuit .Dear MikeMI the very first step of my design is to configure out a transmitter circuit with a output wattage as much as possible.I don't mean Inductors ,I really mean RFC coils ( so-called chokes) like this one VK200 tosk component They are very rare in my country,Myanmar .Dear MikeMI ,Can't I build a transmitters circuit using transistors and other radio components because tubes that you said are also scare and very complicate to handle ? Forwarding your warmly suggestions to my circuit design MileMI
 

Mg Myo Ko

New Member
Thanks million & millions!

In reality, the range of any radio transmitter isn't so much dependant on modulation type as much as frequency. There are optimal frequency bands between 160 meters and 6 meters which can transmit a great distance given ionospheric conditions and sunspots.

FM is typically not used in lower frequency radio because of the bandwidth requirements and the available "real estate".

In your case, it sounds like you want to use the accepted "commercial" frequencies for FM radio, for which recievers are commonplace. This would typically limit transmissions to Line-of-site and a measure beyond depending on terrain, amplifier power, and antenna height,construction. You would be amazed at how much you can do with very little power. I have QSL cards using CW (morse code) communication from clear around the world using less than 1 watt.

A few suggestions that might "help", assuming you can construct a maximized transmitter...

Antenna height. If you are in a mountainous area, that tiny transmitter might surprise you at elevation. If you are doing this for fun and not a permenant set-up, you may think of a portable radio station on a mountaintop. If you have the ability to weather-proof your equipment and have sufficient battery power, and a secret location, you might have fun doing it that way with an automated transmitter.

ANTENNA. You mention 5-miles *around*, and this would be a typical omnidirectional vertical antenna, but a resonant wire dipole will give you bidirectional coverage...if you aim at population centers you will achieve some gain (which is a misnomer in a way, but in other words you concentrate the transmission and reduce loss)

LOSS...important concept. Transmission lines intoduce loss with standing waves and resistance. The better your transmission line and all of your connections, and the shorter the line, the more use of your transmitting power that will not be wasted as heat.

If you have the inclination, a YAGI style antenna (think outdoor tv antenna) has maximized gain in a single direction. The reflector dipole elements help focus transmitter power. Multi-element yagis further do this. It is the equivelant of mirrors and lenses in an optical system, only with radio waves.

The antenna needs to be a full wavelength above ground, more if you can. Given a 10 meter antenna as an example, it will work optimally at 30+ feet above the ground.

Also, some evidence shows transmitting across saltwater helps with gain, though I doubt this will apply in what you are doing.

Some or none of this info might help you, but perhaps you did learn something new or someone else.

Oh one more thing...polarization. (Most) Any antenna style can be polarized vertically or horizontally, and with short range transmitters (for which even 5 mile radius includes) it is important that the recieving station be polarized the same way, It has been a while since I played with my radios and built antennas, but 10-100 dB of loss occurs with cross-polarization.

It might be educational and fun for you to refer to the radio amateur's antenna handbook and googling "radio antenna", "dipole", "yagi", etc to get construction ideas and formulas for your frequency specifics.

Remember, a resonant antenna is by definition a function of radio frequency. A dipole is 1/2 wavelength, with 1/4 for each element to be efficient. There are off-center and multi-wavelength designs as well that give differing patterns for the transmission, but it is very hard to beat the standard 1/2 wave dipole.

And for transmission line, if you have the ability to match the impedance of your transmitters amplifier properly, parallel ladder line is very good, low loss stuff and you can construct it yourself with copper wire and popcycle sticks.

It is IMPERATIVE though, for the sake of your transmitter amplifer, that the impedance of your antenna is matched to the output impedance of the power transistor. Matching networks can be built, and that is, unfortunatley, where RLC circuits are neccessary.

However, matching can be done with the dimensions of the ladderline as well, along with methods you can employ found all over the internet.

Bad consideration is that many of these projects require at a minimum an SWR meter or an antenna analyzer to tune them to resonance.

Thanks is more than millions for your appreciable information .Dear ke5frf ,the first step to my circuit design is to consider an oscillatory circuit whose frequency is somewhere between 88-108MHz (commercial band ) and with a output wattage as much as possible .This circuit can contain RF components such as inductors ,transistors , capacitors and so on. What I don't want is only RFC chokes (like VK200 tosk component) .The most matters is that I don't have enough knowledge to design an oscillatory circuit with stable conditions and that is the very reason that I ask for anybody 'help in this forum , After I have had a transmitter ,the antenna is in vital role and this section will cover all your discriptions you mentioned .So looking forward your valuable advice warmly and thanks again for your time really .
 
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