User:Mu301/Experimental Radio

Experimental Radio is a license-free form of radio communications. It differs from amateur radio in that it uses very low power transmitters that are exempt from license requirements. The frequency bands and the transmitter power allowed for unlicensed operation vary from place to place - please check the local regulations for your area before experimenting.

Experiments
The first experiments to be described here will involve using off-the-shelf electronic test equipment as a makeshift transmitter in the Medium wave band. Later experiments will involve the construction of a commercial transmitter kit.

A radio transmitter generates a carrier wave which can then be fed to an antenna to propagate the signal. Information can be encoded on the carrier wave by turning it on and off, or by using some form of modulation. The former is often used to transmit a message using Morse code, while the latter is used to send voice transmissions.

A signal generator transmitter
A signal generator that is capable of producing high frequency signals can be used as a simple source for a carrier wave. These may be obtained on the used market at reasonable cost. It is desirable to have a generator that is capable of modulating the signal. For experiments in the Medium wave band the carrier should be in the range of 510 - 1705 kHz. In the United States it is permissible to transmit up to 1/10 Watt into a 3 meter antenna without an FCC license. Care should be taken to select a frequency which is not being used by any nearby commercial broadcast station. There are a number of online tools that can help with this, for example: AM Radio Database Query.

Example
A check of the AM Radio Database shows that there are no commercial stations near the location of the experimental transmitter that are using the frequency of 1580 kHz. The signal generator is set to produce a sine wave at this frequency and is then amplitude modulated with a 1000 Hz sine wave. The amplitude of the signal should be in the range of 1.6 - 2 Volts RMS. The output of the generator is attached to a piece of loose wire less than 3 meters long which is used as a makeshift antenna. A standard AM radio receiver is then set to the same frequency and the presence of a tone indicates reception of the signal.

Wikipedia

 * LowFER Low-Frequency Experimental Radio (also discusses MedFER and HiFer for Medium and High Frequency)
 * Microbroadcasting
 * Low-power broadcasting

Longwave Club of America

 * Longwave Home Page
 * What Is 'Part 15?'
 * Part 15 Operation broken link
 * Receiver and Antenna Files broken link

AM88 Low Power Transmitter

 * AM88 Transmitter Kit
 * AM88 Part 15 operation
 * LP AM Vertical Antenna with loading coil
 * Variometer Loading Coils For LP AM Antennas
 * Construction of a Vertical Antenna for Part 15 AM Broadcast use