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Increasing range - matching coils for low power AM transmitters

Our Low Power Radio mailbag often gets questions about increasing range for AM transmitters by focusing on antennas - "What kind of antenna will increase my range?" "Will a long wire increase my range?" "Can a different antenna get my signal out farther?"
     Of course, you could always stretch out a half wave dipole - around 310 feet should do it at 1500 KHz or 155 feet per leg. The FCC might frown on that, as you would likely exceed the allowable field strength and you wouldn't be compliant with the alternate limit of a 3 meter (9'8") antenna :-) probably for the best, can you imagine managing a 300 foot antenna? Sheesh!
     Most low power AM broadcasters stick to the 3 meter antenna and try to improve range with an antenna matching coil.  This makes 'antenna design' very simple - get something conductive that is around ten feet long - done!  Low power AM broadcasters use copper pipe or tubing, aluminum tubing, light or heavy gauge copper wire or even the shield of a length of coax supported by plastic pipe, old TV antenna mast - anything that conducts electricity and that can be isolated from ground.  In this configuration, it's the matching coil that really makes the antenna.
     The worst mistake I made was thinking matching coils were an exact science when the exact opposite is true - matching coils can be big or small, air coil or iron powder (but never ferrite) core, horizontal, vertical, wound around a toroid or any combination of these. Once a coil is wound on its core, the inductance of the coil can be changed by tapping the coil at specific windings, by stretching or compressing the coil windings on the form or by connecting several smaller coils (even of different types) in series to add together for more inductance. Your imagination is the only limit!
     There is far too much information to share an a simple blog post, so please to be enjoying our many annotated links to readings about building antenna matching coils to increase range in low power AM broadcasting. As always, intellectual property and quoted content from the sites below are © the original authors of the linked works:
So do some reading, pick up a few simple parts and supplies and start extending the range of your low power AM transmitter using your new skills in building matching coils!

1 comment:

John Stuart said...

Great series of articles!! Very informative. Well written. BRAVO!!