Editing Shortwave radio (section)

==Types of modulation==
{{further|Modulation}}
[[Image:Shortwave Radio.jpg|thumb|right|[[National Panasonic]] R3000 [[Analogue electronics|analog]] shortwave [[radio receiver]], {{Circa|1965}}.<ref name=SWRad_Panasonic/>]]
Several different types of [[modulation]] are used to incorporate information in a short-wave signal.

===Audio modes===
====AM====
[[Amplitude modulation]] is the simplest type and the most commonly used for [[International broadcasting|shortwave broadcasting]]. The instantaneous amplitude of the carrier is controlled by the amplitude of the signal (speech, or music, for example). At the receiver, a simple [[Detector (radio)|detector]] recovers the desired modulation signal from the carrier.<ref name=RohdeWhitaker2000/>

====SSB====
[[Single-sideband modulation|Single-sideband]] transmission is a form of amplitude modulation but in effect filters the result of modulation. An amplitude-modulated signal has frequency components both above and below the [[carrier frequency]]. If one set of these components is eliminated as well as the residual carrier, only the remaining set is transmitted. This reduces power in the transmission, as roughly {{frac|2|3}} of the energy sent by an AM signal is in the carrier, which is not needed to recover the information contained in the signal. It also reduces signal [[Bandwidth (signal processing)|bandwidth]], enabling less than one-half the AM signal bandwidth to be used.<ref name=RohdeWhitaker2000/>

The drawback is the receiver is more complicated, since it must re-create the carrier to recover the signal. Small errors in the detection process greatly affect the pitch of the received signal. As a result, single sideband is not used for music or general broadcast. Single sideband is used for long-range voice communications by ships and aircraft, [[citizen's band]], and amateur radio operators. In amateur radio operation lower sideband (LSB) is customarily used below 10&nbsp;MHz and USB (upper sideband) above 10&nbsp;MHz, non-amateur services use USB regardless of frequency.

====VSB====
[[Vestigial sideband]] transmits the carrier and one complete sideband, but filters out most of the other sideband. It is a compromise between AM and SSB, enabling simple receivers to be used, but requires almost as much transmitter power as AM. Its main advantage is that only half the bandwidth of an AM signal is used. It is used by the Canadian standard [[time signal]] station [[CHU (radio station)|CHU]]. [[Single-sideband modulation#Vestigial sideband (VSB)|Vestigial sideband]] was used for analog television and by [[ATSC standards|ATSC]], the [[8VSB|digital TV]] system used in North America.

====NFM====
Narrow-band [[frequency modulation]] (NBFM or NFM) is used typically above 20&nbsp;MHz. Because of the larger bandwidth required, NBFM is commonly used for [[VHF]] communication. Regulations limit the bandwidth of a signal transmitted in the HF bands, and the advantages of frequency modulation are greatest if the FM signal has a wide bandwidth. NBFM is limited to short-range transmissions due to the multiphasic distortions created by the ionosphere.<ref name=Sinclair2000/>

====DRM====
[[Digital Radio Mondiale]] (DRM) is a digital modulation for use on bands below 30&nbsp;MHz. It is a digital signal, like the data modes, below, but is for transmitting audio, like the analog modes above.

===Data modes===
====CW====
[[Continuous wave]] (CW) is [[on-off keying|on-and-off keying]] of a sine-wave carrier, used for [[Morse code]] communications and [[Hellschreiber]] [[facsimile]]-based [[teleprinter]] transmissions. It is a data mode, although often listed separately.<ref name=FeldHellFAQ/> It is typically received via lower or upper SSB modes.<ref name=RohdeWhitaker2000/>

====RTTY, FAX, SSTV====
[[Radioteletype]], fax, digital, [[slow-scan television]], and other systems use forms of frequency-shift keying or audio subcarriers on a shortwave carrier. These generally require special equipment to decode, such as software on a computer equipped with a sound card.

Note that on modern computer-driven systems, digital modes are typically sent by coupling a computer's sound output to the SSB input of a radio.