# How to amplify arduino AM radio transmitter

I plan to make long distance radio transmitter, and transmit morse code with it.
I found this:

And it works very well but how can I amplify it?
I tried with transistor but it didn’t helped. What can I do to amplify it?
Thanks for any help

You cant . To get any kind of range from such a transmitter, you need an efficient antenna, and as the frequency is only 800 Khz , you cant make one.

Thanks for your reply I added antenna with 2 meters length. And what if I increase frequency?

Try increasing the frequency to around 400 Mhz , then you can make a simple antenna that will work.

Nikodem: I plan to make long distance radio transmitter, and transmit morse code with it.

I'm curious, when you said long distance, what is the distance? 100 meter? 1kM? 10KM? 100KM?

Nikodem: Thanks for your reply I added antenna with 2 meters length. And what if I increase frequency?

For 800 KHz, wavelength is 375 Meters, 1/4 wavelength will be 46.875 meters. So you antenna need 46.875 meters.

A 1/4 wave antenna has pretty low impedance if properly tuned, so if you try this, there is a good chance of destroying the output pin.

Because the output is nominally a square wave, not a sinusoid wave, you're emitting strongly at odd harmonics. That is, you'll have the desired first order signal at 800 kHz, but undesired emissions at 3*800 = 2.4 MHz, 5*800 = 4.0 MHz, 7*800 = 5.6 MHz and so forth. With low signal power and an inefficient antenna no one is going to notice or care, but if you amplify this and use an efficient antenna without proper band limiting, you're liable to tick someone off.

This is a toy circuit, don't mistake it for a proper long distance radio.

Thanks for all of reply. I understand it better right now. Long distance for me is >100km. So, the easiest way to make it is:

And how can I amplify it to get 100km range

And how can I amplify it to get 100km range

You do know that it will be illegal if you do this don't you?

You cant get 100 kms no matter what you do. As an example, a typical AM radio broadcast station which is the most common type that you pick up on a crystal set, uses a 1/4 wave vertical antenna , and a very extensive ground plane made of multiple radials buried in the ground. But the killer is the transmit power thats needed, typically anywhere from 5 KW up to 50 KW - 100 KW. You may be able to make a few milliwatts. The simplest way to play around with radio transmission and Arduinos is to buy something like one of these. http://www.miniinthebox.com/diy-433mhz-wireless-receiving-module-for-arduino-green_p411878.html You wont get anything like 100 kms, more like 100 metres, but at least you will have something that works.

Legality of it depends on the frequency. I like to use it in high altitude balloon so 100m, 1km and 10km it's to less

Legality of it depends on the frequency.

No not in any way. If you make a transmitter without a license to make one you break the law no matter what frequency it is on.

If you operate a transmitter on a frequency you are not licensed to use that is illegal.

Beware of the so called license free bands, you can only operate type approved equipment, not home made or home modified to increase the range equipment.

Not exactly Mike. It depends, some what, on location. but in most places, there are frequencies in which you can operate low power and 'homemade' transmitters. It depends upon the local laws, but most conform to international agreement, Frequency, and Power.

And how can I amplify it to get 100km range

I suggest to study up for and pass the exam for an Amateur Radio Operator's license. Then you are welcome to transmit on certain bands, with enough power to easily reach 100 km.

123Splat: in most places, there are frequencies in which you can operate low power and 'homemade' transmitters.

Some not most. For example it is illegal in the whole of Europe. The OP wants 100km range - no way that is legal where ever you are.

jremington: I suggest to study up for and pass the exam for an Amateur Radio Operator's license. Then you are welcome to transmit on certain bands, with enough power to easily reach 100 km.

Exactly - learn - get a license - then we can help. Show the level of ignorance shown by:-

And it works very well but how can I amplify it? I tried with transistor but it didn't helped.

And you are menace in the RF spectrum and we can all do without that.

I didn't know about it. I thought that on some frequencies it is legal :( I am not good at electronics so I didn't know about technical barriers Thanks for help.

Grumpy_Mike: No not in any way. If you make a transmitter without a license to make one you break the law no matter what frequency it is on.

If you operate a transmitter on a frequency you are not licensed to use that is illegal.

Beware of the so called license free bands, you can only operate type approved equipment, not home made or home modified to increase the range equipment.

Actually, Mr. Grumpy pants, if you're a licensed amateur radio operator, you're allowed to build all the transmitters you want (and use them) as long as they're not causing interference or noise on bands you're not licensed to transmit on and as long as it's on the bands you're licensed for.

Quit shooting down this persons dream and ruining their fun and curiosity. There used to be a ton of hams willing to teach curious young people how to build radios and stuff now it's just a bunch of angry old dudes that say "go buy this or that radio" among a whole other slew of things they say you need. This person is obviously asking about radio, probably with an interest in amateur radio.

Screw what these guys have to say, honestly you've got me looking at arduinos as an alternative to crystals because they're flexible and I have 3 of them. Thanks! Message me with updates and maybe we can collaborate on this. Also, don't forget crystals as an option, or if you're set on a chip, TI makes synthesizer chips that are already proven for such an application...maybe one of those could more effectively create the frequency desired and then be controlled via arduino.

@KF5EGM, if you think you can meet the standards in FCC rules, Part 97.307 (as well as the licensing criteria) then "knock yourself out".

It seems odd Ms. Chloe Stratton that you registers on this forum just to have a go at me.

Actually, Mr. Grumpy pants, if you're a licensed amateur radio operator, you're allowed to build all the transmitters you want (and use them) as long as they're not causing interference or noise on bands you're not licensed to transmit on and as long as it's on the bands you're licensed for.

Then the OP would have a license which is what I said in that quote of mine you posted.

But it is EXACTLY what we are both saying, get a license. I got my license in 1973 and I even taught a class at a local FE collage on the theory you needed to pass the exam. The U.S. ham license is less restricted than the UK one but it still has its rules. In my reply #13 I said:-

• learn - get a license - then we can help.

Most posters here on the subject of radios have no idea that it is illegal to make a transmitter to operate in the unlicensed bands. That applies to the U.S. as well. It is this fact that we are putting before them. Most are not interested in radio but just want to save money on a gadget.

Quit shooting down this persons dream and ruining their fun and curiosity.

Well:-

“If you trust in yourself. . .and believe in your dreams. . .and follow your star. . . you'll still get beaten by people who spent their time working hard and learning things and weren't so lazy.” ― Terry Pratchett, The Wee Free Men

KF5EGM:
Actually, Mr. Grumpy pants, if you’re a licensed amateur radio operator, you’re allowed to build all the transmitters you want (and use them) as long as they’re not causing interference or noise on bands you’re not licensed to transmit on and as long as it’s on the bands you’re licensed for.