A tikker, alternately spelled ''ticker'', was a vibrating interrupter used in early

wireless telegraphy Wireless telegraphy or radiotelegraphy is transmission of text messages by radio waves, analogous to electrical telegraphy using cables. Before about 1910, the term ''wireless telegraphy'' was also used for other experimental technologies for ...

radio receiver In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. Th ...

s such as

crystal radio A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio. It uses only the power of the received radio signal to produce sound, needing no external power. It is named for its most imp ...

receivers in order to receive

continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or partic ...

(CW)

radiotelegraphy Wireless telegraphy or radiotelegraphy is transmission of text messages by radio waves, analogous to electrical telegraphy using cables. Before about 1910, the term ''wireless telegraphy'' was also used for other experimental technologies for t ...

signals. In the early years of the 20th century, before modern AM or FM radio transmission was developed, radio transmitters communicated information by

; the transmitter was switched off and on by the operator with a

telegraph key A telegraph key is a specialized electrical switch used by a trained operator to transmit text messages in Morse code in a telegraphy system. Keys are used in all forms of electrical telegraph systems, including landline (also called wir ...

, producing pulses of radio waves, to spell out text messages in

Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...

. Around 1905 the first

radio transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...

s began to replace the earlier spark transmitters. The Morse code signal of the spark transmitter consisted of pulses of radio waves called

damped wave Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples i ...

s which repeated at an audio rate, so they were audible as a buzz or tone in a receiver's earphones. In contrast the new continuous wave transmitters produced a signal consisting of pulses of

s, unmodulated sinusoidal

carrier wave In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has ...

s, which were inaudible in the earphones.K. G. Beauchamp,''History of telegraphy'', IET, 2001 , page 201 So to receive this new modulation method, the receiver had to produce a tone during the pulses of carrier. The "tikker", invented in 1908 by

Valdemar Poulsen Valdemar Poulsen (23 November 1869 – 23 July 1942) was a Danish engineer who made significant contributions to early radio technology. He developed a magnetic wire recorder called the telegraphone in 1898 and the first continuous wave rad ...

, was the first primitive device that did this. It consisted of a vibrating switch contact between the receiver's detector and earphone, which was repeatedly opened by an

electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in ...

. It functioned as a crude

modulator In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...

; it interrupted the signal from the detector at an audio rate, producing a buzz in the earphone whenever the carrier was present. Thus the "dots" and "dashes" of the Morse code were made audible. Around 1915 the tikker was replaced by a better means of accomplishing the same thing; the "heterodyne receiver" invented by

Reginald Fessenden Reginald Aubrey Fessenden (October 6, 1866 – July 22, 1932) was a Canadian-born inventor, who did a majority of his work in the United States and also claimed U.S. citizenship through his American-born father. During his life he received hundre ...

in 1902. In this an

electronic oscillator An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillators convert direct current (DC) from a power supply to an alternating ...

generated a radio signal at a frequency ''f''_o offset from the incoming radio wave carrier ''f''_C. This was applied to the rectifying

detector A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...

with the radio carrier. In the detector the two signals mixed, creating a heterodyne (beat) signal at the difference ''f''_C - ''f''_C between these frequencies, which was in the audio frequency range. The heterodyne provided the audible tone in the earphone whenever the carrier was present. After vacuum tube oscillators were invented in 1913 by

Alexander Meissner Alexander Meissner (in German: Alexander Meißner) (September 14, 1883 – January 3, 1958) was an Austrian engineer and physicist. He was born in Vienna and died in Berlin. His field of interest was: antenna design, amplification and detectio ...

the heterodyne receiver replaced the tikker. Today the heterodyne method is still used to receive CW signals, and the ''

beat frequency oscillator In a radio receiver, a beat frequency oscillator or BFO is a dedicated oscillator used to create an audio frequency signal from Morse code radiotelegraphy ( CW) transmissions to make them audible. The signal from the BFO is mixed with the receive ...

'' (BFO) is a standard part of all

communications receiver A communications receiver is a type of radio receiver used as a component of a radio communication link. This is in contrast to a ''broadcast receiver'' which is used to receive radio broadcasts. A communication receiver receives parts of the r ...

References

Radio technology {{radio-comm-stub