In amateur radio, QRP operation means transmitting at reduced power levels while aiming to maximize one's effective range while doing so. The term QRP derives from the standard Q code used in radio communications, where "QRP" and "QRP?" are used to request, "Reduce power", and ask "Should I reduce power?" respectively. The opposite of QRP is QRO, or high-power operation.
Most amateurs use approximately 100 watts on HF and 50 watts on VHF/UHF, but in some parts of the world, like the US, they can use up to 1500 watts. QRP enthusiasts contend that this is not always necessary, and doing so wastes power, increases the likelihood of causing interference to nearby televisions, radios, and telephones and, for United States' amateurs, is incompatible with FCC Part 97 rule, which states that one must use "the minimum power necessary to carry out the desired communications".
There is not complete agreement on what constitutes QRP power. While most QRP enthusiasts agree that for CW, AM, FM, and data modes, the transmitter output power should be 5 watts (or less), the maximum output power for SSB (single sideband) is not always agreed upon. Some believe that the power should be no more than 10 watts peak envelope power (PEP), while others strongly hold that the power limit should be 5 watts. QRPers are known to use even less than five watts, sometimes operating with as little as 100 milliwatts or even less. Extremely low power—1 watt and below—is often referred to by hobbyists as QRPp.
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 systems and enhanced operating skills.
Some extreme QRP enthusiasts use QRSS — transmitting extremely slowly — to compensate for the decreased signal-to-noise ratio involved in QRP operation. QRSS derives from the standard Q code used in radio communications, where "QRS?" asks "Shall I send more slowly?" and "QRS" requests "Send more slowly".
Rather than directly listening to such slow transmissions, many QRSS enthusiasts record the transmission for later analysis, later decoding "by ear" while playing it back at much faster rates (time compression), or decoding "by eye" on the waterfall display of a spectrum analyzer.
QRSS enthusiasts typically use some form of Morse code, except much slower — rather than a typical 1/100 second "dit" time, QRSS transmissions may use a full second for the "dit" time, or in extreme cases, a full minute for a single "dit" time.
- Morse code with standard on-off keying
- FSCW (Morse code with frequency-shift keying), where "key up" is one frequency, "key down" is another frequency.
- DFCW or Dual Frequency CW, where "dit" is one frequency, "dah" is a different frequency, and spaces have no carrier or a third carrier frequency. With DFCW, the "dah" time is typically shortened to the same length as the "dit" time, and the short space between "dit" and "dah" in a letter is often eliminated.
Many of the larger, more powerful commercial transceivers permit the operator to lower their output level to QRP levels. Commercial transceivers specially designed to operate at or near QRP power levels have been commercially available since the late 1960s. In 1969, American manufacturer, Ten-Tec, produced the Powermite-1 (PM-1). This radio was one of Ten-Tec's first assembled transceivers. (The MR-1 was available, and it was essentially the same radio, albeit in kit form.) This radio featured modular construction (all stages of the transceiver were on individual circuit boards): the transmitter was capable of about one or two watts of RF, and the receiver was a direct-conversion unit, similar to that found in the Heathkit HW-7 and HW-8 lines. Many amateurs became quite adept at QRP'ing through their use of these early, trend-setting radios. As QRP has become more popular in recent years, radio manufacturers have introduced radios specifically intended for the QRP enthusiast. Popular US models include Elecraft KX3, K2 and K1, the Yaesu FT-817, the Icom IC-703, and the Argonaut V and the new 539 Argonaut VI from TenTec. Popular German QRP transceiver kits include the SOLF, Moskita, Sparrow, Hegau, Hohentwiel, Tramp-8 CW and others. Another popular source is Hendricks QRP Kits, which offers a variety of popular kits. HFPack enthusiasts operate QRP radios on the HF bands in portable modes, usually carrying the radios in backpacks, with whip antennas.
Some QRPers prefer to construct their equipment from kits or homebrew it from scratch.
Contests and awards 
In the USA, the November Sweepstakes, June and September VHF QSO Parties, January VHF Sweepstakes, and the ARRL International DX Contest, as well as many major international contests have designated special QRP categories. For example, during the annual ARRL's Field Day contest, making a QSO (ham-to-ham contact) using "QRP battery power" is worth five times as many points as a contact made by conventional means.
The QRP ARCI club sponsors 12 contests during the year specifically for QRP operators. QRP-ARCI Contests
Typical awards include the QRP ARCI club's "thousand-miles-per-watt" award, available to anyone presenting evidence of a qualifying contact. QRP ARCI also offers special awards for achieving the ARRL's Worked All States, Worked All Continents, and DX Century Club awards under QRP conditions. Other QRP clubs also offer similar versions of these awards, as well as general QRP operating achievement awards.
See also 
- VOACAP Analysis of a isotrope antenna for 20m band located in JO40 at 23h: comparing 1W vs. 99W output power. http://gerolfziegenhain.blogspot.de/2012/07/hf-propagation-simulation-influence-of.html
- "QRSS Knights grabber compendium"
- "QRSS and You: Using absurdly low-speed CW for "communications" (As well as other ultra-narrowband modes)"
- QRPproject! Devoted to QRP and Amateur Radio homebrewing
- http://www.arrl.org/tis/info/qrpwhtwy.html ARRL, QRP: What, Why and How
- Forum dedicated to QRP operation
- QRP WebRing Home
- QRPedia wiki
- American QRP Club
- VKQRP Club - CW Operator's QRP Club Inc.
- Four State QRP Group
- GQRP Club
- New England QRP Club
- New Jersey QRP Club
- North Georgia QRP Club
- NORTEX - North Texas QRP Club
- Flying Pigs QRP Club International
- North American QRP CW Club
- Northern California QRP Club
- QRP Amateur Radio Club International
- The Eastern PA QRP Club
- The Colorado QRP Club
- QRPer.com - a QRP website specializing in portable & field operations
- PortableQRP.com many example videos on QRP operation PortableQRP
- 5000+ Member SoftRock Low Cost Software Defined QRP Radio Kit Interest Group
- EAQRP, Website of Spanish QRP Association
- Blog del radioclub Liria, Spanish Amateur Radio club dedicated to qrp and homebrew
- Ten Tec AC-5 Antenna tuner video
- QRP Building Tips