Editing QRP operation (section)

== Practice ==
[[File:QRP HF Coverage 1W vs 99W.png|thumb|[[VOACAP]] simulation of propagation against distance, comparing effective radiations of 1 watt (top) and 99&nbsp;watts (bottom).]]
The practice of operating with low power was popularized as early as 1924, with a variety of reports, editorials and articles published in U.S. amateur radio magazines and journals that encouraged amateurs to lower power output, both for purposes of experimentation, and for improving operating conditions by reducing interference.<ref name="HistoryOfQRP">
{{cite book
 |last=Weiss |first=Adrian
 |year=1987
 |title=History of QRP in the U.S., 1924-1960
 |location=Vermillion, SD
 |publisher=Milliwatt Books
 |isbn=978-0-9614139-1-0 |ol=2411449M
}}
</ref>

Although not universally agreed upon, the ARRL makes a recommendation for QRP power limits. Most amateur organizations agree that for [[Morse code|CW]], [[Amplitude modulation|AM]], [[Frequency modulation|FM]], and [[data]] [[Modulation|modes]], the [[transmitter]] [[transmitter power output|output power]] should be 5 [[watt]]s (or less).<ref>
{{cite book
 |last=Rutledge |first=David |author-link=David Rutledge (engineer)
 |year=1999
 |title=The Electronics of Radio
 |publisher=Cambridge University Press
 |page=312
 |isbn=978-1-107-39366-0
 |url=https://books.google.com/books?id=ccQLAQAAQBAJ&q=QRP&pg=PA312
 |via=Google Books
}}
</ref> The maximum output power for [[single-sideband modulation|SSB]] (single sideband) is sometimes agreed to be no more than 10&nbsp;Watts [[peak envelope power]] (PEP), while some organisations opine that the power limit should be 5&nbsp;Watts. QRPers are known to regularly use less than 5&nbsp;Watts, sometimes operating with as little as 100&nbsp;milliwatts or even less. Extremely low power — 1&nbsp;Watt and below — is often referred to by hobbyists as "QRPP".<ref name=Wells/><ref name=Arland2007/><ref name=Dobbs2012/><ref name=DeMaw1991/>

Communicating using QRP can be difficult since the QRPer must face the same challenges of [[radio propagation]] faced by amateurs using higher power levels, but with the inherent disadvantages associated with having a weaker signal on the receiving end, all other things being equal. QRP aficionados try to make up for this through more efficient [[antenna (radio)|antenna]] systems and enhanced operating skills.<ref name=DeMaw1991>
{{cite book
 |first=Doug |last=DeMaw
 |year=1991
 |title=W1FB's QRP Notebook
 |publisher=[[American Radio Relay League]]
 |isbn=978-0-87259-365-7
 |url=https://books.google.com/books?id=hPBINAAACAAJ
 |via=Google Books
}}
</ref><ref name="Silver2018" />

=== Weak signal modes ===
QRP enthusiasts may use special modes that employ technology and software designed to enhance reception of the relatively weak transmitted signals resulting from low power levels.<ref name=WSM/>

'''QRSS''': Very slow speed Morse code 
:QRSS uses very slow speed [[continuous wave|CW]] (Morse code) to compensate for the decreased [[signal-to-noise ratio]] involved in QRP operation.<ref name=WSM/>{{efn|''QRSS'' is an exaggerated version of '''QRS''', the standard [[Q code]] used in radio communications. "'''QRS?'''" asks "''Shall I send more slowly?''".<ref name=Marchant>
{{cite book
 |last=Marchant |first=William Henry
 |year=1914
 |title=Wireless Telegraphy: A handbook for the use of operators and students
 |publisher=Whittaker
 |page=[https://archive.org/details/wirelesstelegra00marcgoog/page/n236 220]
 |url=https://archive.org/details/wirelesstelegra00marcgoog
 |via=Archive.org
}}
</ref>}} QRSS enthusiasts may record a transmission for later analysis, sometimes decoding "by ear" while playing it back at much faster speeds, or decoding "by eye" on the waterfall display of a spectrum analyzer.<ref name=DennisonFielding2007>
{{cite book
 |first1=Mike |last1=Dennison
 |first2=John |last2=Fielding
 |year=2007
 |title=Radio Communication Handbook
 |publisher=[[Radio Society of Great Britain]] (RSGB)
 |isbn=978-1-905086-33-7
 |url=https://books.google.com/books?id=f6AeAQAAIAAJ
 |via=Google Books
}}
</ref><ref>
{{cite web
 |title=Grabber compendium
 |department=QRSS Knights
 |website=digilander.libero.it
 |publisher=I2NDT
 |place=Bergamo, IT
 |url=http://digilander.libero.it/i2ndt/grabber/grabber-compendium.htm
}}
</ref>

'''Coherent CW''': Critically-timed Morse code transmission
:Coherent CW uses transmitters that clock-out signals calibrated to a precise rate, allowing receivers to employ extremely narrowband filtering to increase readability.<ref name=WSM/>

'''[[WSJT (amateur radio software)|WSJT]]''': Weak Signal – Joe Taylor
:WSJT is a software system that utilizes several separate modes, each optimized for a different signal path; these include [[Meteor burst communications|meteor scatter]], [[troposcatter]], and [[Earth–Moon–Earth communication|EME communications]]. WSJT was named after [[Joseph Hooton Taylor Jr.|Dr. J.H. Taylor]] to acknowledge his work in developing weak signal communication modes for radio.<ref name=WSM/>{{efn|Dr. [[Joseph Hooton Taylor Jr.]] is an astrophysicist who won the [[Nobel Prize in Physics]] in 1993 for discovery of a new type of [[pulsar]] which is useful for the study of [[General Relativity]] by [[radio astronomy]]. He is an [[amateur radio]] operator (currently K1JT), and has generously contributed his technical expertise to the development of successful transmission of weak signals over otherwise rarely usable propagation paths.}}

'''[[WSPR (amateur radio software)|WSPR]]''':  Weak Signal  –  Propagation Reporter
:WSPR is a software suite and computer network used to monitor propagation paths for optimal communication conditions.<ref name=WSM>
{{cite web
 |title=Weak signal modes
 |website=ARRL.org
 |publisher=[[American Radio Relay League]]
 |url=http://www.arrl.org/weak-signal-modes
 |access-date=24 November 2019
}}
</ref>