Motorboating
Encyclopedia
Motorboating is one of many problems that can afflict radio transmitters and similar devices. Radio transmitters are vulnerable to unwanted feedback; one possible symptom of unwanted feedback are rapid changes in power output, which repeats about 20 to 20,000 times per second; this is called motorboating because when the radio transmission is received, it resembles the sound of a motorboat engine.
problem where Radio frequency
(RF) from a device leaves through one route and then re-enters the unit through another conduit where it causes an increase in the level of the RF generated by the unit. When this RF output climbs above a given level a catastrophic
change occurs which causes the RF power output to drop rapidly. This causes a series of audio
frequency pulses to be generated, in an AM
system these can be heard clearly as a sound which is like the engine of a motorboat.
In general, as the intended RF power
output of the device is increased the possibility of motorboating is increased. If motorboating is occurring in a system then the rate of the low frequency oscillation
will increase.
into the system then the output will be a function of the RF input.
If the RF leaks into the device which generates the RF it can alter the RF power output, it might cause an increase in the RF power level, which in turn leads to an increase of the effect which causes the effect increasing the RF output to increase. This, if unchecked, will lead to a greater and greater increase in power output.
Assuming that the device does not fail due to this power surge
, then it is likely that the system will reach a state where it is either insensitive to any further increase in RF input (then the power increase will cease), or a sudden catastrophic change will occur to state where the RF power output is smaller. The second of these cases can lead to an oscillation.
s which link the supply wires to the RF
ground (case) are missing then it is possible for RF to enter the radio set through the supply wires. This then causes the motorboating to occur.
Technical description
Motorboating is a term for a self-inflicted EMCElectromagnetic compatibility
Electromagnetic compatibility is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such energy may induce...
problem where Radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
(RF) from a device leaves through one route and then re-enters the unit through another conduit where it causes an increase in the level of the RF generated by the unit. When this RF output climbs above a given level a catastrophic
Catastrophe theory
In mathematics, catastrophe theory is a branch of bifurcation theory in the study of dynamical systems; it is also a particular special case of more general singularity theory in geometry....
change occurs which causes the RF power output to drop rapidly. This causes a series of audio
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
frequency pulses to be generated, in an AM
AM broadcasting
AM broadcasting is the process of radio broadcasting using amplitude modulation. AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is carried out in the medium wave band world wide, and on long wave and short wave...
system these can be heard clearly as a sound which is like the engine of a motorboat.
In general, as the intended RF power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
output of the device is increased the possibility of motorboating is increased. If motorboating is occurring in a system then the rate of the low frequency oscillation
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
will increase.
Theory
If an electronic device is considered as a black box whose output is related to a series of inputs by a mathematical function, then if one of the inputs to the device is leaking RFRadio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
into the system then the output will be a function of the RF input.
If the RF leaks into the device which generates the RF it can alter the RF power output, it might cause an increase in the RF power level, which in turn leads to an increase of the effect which causes the effect increasing the RF output to increase. This, if unchecked, will lead to a greater and greater increase in power output.
Assuming that the device does not fail due to this power surge
Voltage spike
In electrical engineering, spikes are fast, short duration electrical transients in voltage , current , or transferred energy in an electrical circuit....
, then it is likely that the system will reach a state where it is either insensitive to any further increase in RF input (then the power increase will cease), or a sudden catastrophic change will occur to state where the RF power output is smaller. The second of these cases can lead to an oscillation.
Example
Imagine a 27 MHz CB radioset connected to an external 12 volt DC supply, if the decoupling capacitorCapacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s which link the supply wires to the RF
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
ground (case) are missing then it is possible for RF to enter the radio set through the supply wires. This then causes the motorboating to occur.