AM (Amplitude Modulation)

Information Is Modulated On The Radio Wave Amplitiude. The Frequency Stays Fixed.

AM in DIY Projects is used with cheap remote controls: ASK (Amplitide-Shift keying) is a digital adaption of AM where - in its simplest form (OOK, On-Off-Keying) - the bit 1 is represented as a signal with full amplitude, and the bit 0 is represented by the absence of a signal.

If you want to communicate with remote controls or remotely controlled devices compliant with EV1527, you need an AM sender and receiver.


Initially, Amplitude Modulation was the dominant modulation scheme when radio communication was discovered: it is simple to build, and receivers are simple to make.

Today, AM is still used for simple digital communication (ASK), with some short wave radio stations, in free CB (citizen band) radio, and as one-sided variant (SSB, single side band) by radio amateurs.

The most important use cases for AM today are aviation and simple digital data transmission (ASK modulation).


It did not take long before important disadvantages associated with AM modulation became obvious:

  • Inefficient: AM needs much energy to provide a constant carrier signal onto which the amplitudes can be modulated. Less that 18% of RF power are used to carry information. Since amplitudes swing both ways, and both positive and negative amplitudes carry the same information, 50% of bandwidth (today: scarce allocatable frequencies) is wasted.
  • Jamming and Noise: The amplitude that is carrying the information can easily be jammed by sending a jammer signal slightly offsetting the carrier frequency. Selective carrier loss over great distances can make the signal unreadable. Lightning and any other source of sparks massively interfere with AM.

Today, AM is technically obsolete and replaced by the more efficient and cheaper FM technology.


AM has a few advantages over other modulations which in part is the reason why AM is still used in some areas, i.e. for remote controls and in aviation:

  • Distance: AM can travel long distances and penetrate buildings better than FM. This is valuable both for aviation and for remote controls.
  • Capture Effect: When multiple parties talk at the same time, with AM all parties can still be heard (amplitudes just mix, and weaker stations are just a bit quieter than stronger stations). In FM, the capture effect lets only the strongest station come through.


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(content created Apr 15, 2024)