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 of power, and in some parts of the world like the US, can use up to 1500 watts. QRP enthusiasts contend that this isn't 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.
QRP is especially popular with CW operators and those using the newer digital modes. PSK31 is a highly efficient, narrow-band mode that is very suitable to QRP operation.
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