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As a personal project, I made a very simple AM transmitter with an idea from an online tutorial, using a 1 MHz crystal oscillator (plus power source, antenna, breadboard, etc.).

However, when using an 8 inch wire for the antenna, it is only picked up over a couple feet. How would I make it transmit a longer distance (about 1-2 km)? EDIT: Not 1-2 km anymore, but maybe 50 ft. Either way, I want to understand how it is possible to extend range.

I'm kind of new to electronics and can only understand simple circuits and components like transistor or capacitor, so my online research for this question left me confused. One site mentioned that a good ground is most important for range. If this is true, how do I do this?

Also, I understand that in some countries, there are rules and regulations regarding AM broadcasting. I am doing this in a location where I confirmed that it is okay to do.

Thanks for help!

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  • \$\begingroup\$ You don't, because doing so would not be legal, false claims to the contrary. Even in a setting where licensing were simple or default, equipment would still have to meet technical standards for spectral purity, which rules out gear homebuilt by the uninformed. \$\endgroup\$
    – Chris Stratton
    Dec 28, 2018 at 5:39
  • \$\begingroup\$ @ChrisStratton Running an unlicensed or license free radio IS DEFINATELY ALLOWED if FCC Part 15 (fcc.gov/media/radio/low-power-radio-general-information) compliant. The limitation is power for the transmitter. The distance is 200ft on either the AM or FM band. This type of unlicensed AM/FM use is broadly available in many countries. \$\endgroup\$
    – Jack Creasey
    Dec 28, 2018 at 5:51
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    \$\begingroup\$ @JackCreasey - re-read the question and see the poster's actual goal. \$\endgroup\$
    – Chris Stratton
    Dec 28, 2018 at 5:54
  • \$\begingroup\$ A decent simple antenna at 1MHz is very long (150 m for a half wave solution), Look up base loaded antennas but I would not try and achieve more than the regulatory maximum distance as that is (to put it mildly) frowned upon. \$\endgroup\$
    – Peter Smith
    Dec 28, 2018 at 11:25
  • \$\begingroup\$ Aside from the legality, is the only way to transmit further using a longer antenna? What if I increase frequency? Also, I didn't realize that the limit was 200 ft (the person I asked thought it was 2 km). So, I'm not actually going to build one that transmits 1-2 km. I'm just trying to make a longer distance transmitter as a personal project (not homework) to demonstrate to my physics class. \$\endgroup\$
    – F16Falcon
    Dec 28, 2018 at 16:11

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As others have pointed out, you first need to ensure that you adhere to the relevant standards for TX power in your area, and use a legal frequency.

There are things you can do to get better range. One of them is to make a more sensitive and selective receiver. You could experiment with making a tuned loop antennae - basically a large coil with a cap, forming a tuned circuit, tuned to your transmission frequency. You use a single turn as a feed to your receiver. They are quite directional, so you want to mount it so that you can tweak the position. I've had good results with one of these for picking up UK Am broadcasts on 198kHz, from about 500km away. This should certainly increase the range of your transmission.

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