Five by five
Five by five is the best of 25 possible subjective responses used to describe the quality of communications, specifically the signal-to-noise ratio. As receiving stations move away from an analog radio transmitting site, the signal strength decreases gradually, causing the relative noise level to increase. The signal becomes increasingly difficult to understand until it can no longer be heard as anything other than static.:38
Five-by-five is the best possible Readability and Signal Strength Report previously used by some radio services.
The term has its origins in the Q code used for commercial radiotelegraph communication, and later adopted by other radio services, especially amateur radio. The first number is the answer to the question "How do you receive me?" (Q code QRK), typically answered with "I am receiving (1–5)" where 1 is unreadable and 5 is perfect. The second number is the answer to the question "What is the strength of my signals?" (Q code QSA), typically answered with "The strength of your signals is ... (1 to 5).". "5 by 5" was the answer to the QRK/QSA questions to indicate the best quality signal. "5 by 5" being the best quality was applied to other things by analogy.
The U.S. Army Radio Operator's Manual, FM 24-6 (1945 version) defines the report format as follows:
|2||Readable now and then||Weak.|
|3||Readable but with difficulty||Fairly good.|
|5||Perfectly readable||Very good.|
FM 24-6 further states, "Readability and signal strength reports indicate the desired method of transmission and should be used in that sense. Readability and signal strength reports are not exchanged unless "3" or less, lack of any report being assumed to indicate satisfactory communications."
The report example given uses military call signs and the obsolete Q Code of QJS for readability instead of the current QRK:
|MB6||3MY V MB6 QJS 3 K|
|3MY||MB6 V 3MY INT QJS K|
|MB6||3MY V MB6 QJS 4 AR|
|MB6||S7P V MB6 INT QJS INT QSA K|
|S7P||MB6 V S7P QJS 3 QSA 3 AR|
The modern equivalent of that manual is ACP131(F), which includes these entries:
|Signal||Question||Answer, Advice, or Order|
|QRK||What is the intelligibility of my signals (or those of...)?||The intelligibility of your signals (or those of...) is...
|QSA||What is the strength of my signals (or those of...)?||The strength of your signals (or those of...) is...
In voice procedure (the techniques used to facilitate spoken communication over two-way radios) a transmitting station may request a report on the subjective quality of signal they are broadcasting. In the military of the North Atlantic Treaty Organization (NATO) countries, and other organizations, the signal quality is reported on two scales: the first is for signal strength, and the second for signal clarity or "readability." Both these scales range from one to five, where one is the worst and five is the best. The listening station reports these numbers separated with the word "by". "Five by five" therefore means a signal that has excellent strength and perfect clarity — the most understandable signal possible.
"Five by five" (occasionally written "'5 by 5", "five-by-five", "5 × 5", "5-by-5" or even just "Fives"), by extension, has come to mean "I understand you perfectly" in situations other than radio communication. Further shortened forms are "five by", "fivers" and "fifers". Post-World War II, the phrase "loud and clear" entered common usage with a similar meaning.
The term is arguably derived from the signal quality rating systems such as shortwave's SINPO code[dubious ] or amateur radio's RST code. Given that this slang spans not only generations but also a spectrum of communications technologies (spark-gap transmitters, shortwave, radio telephone, citizen's band (CB) radio, cellular among others) and organizations (hobbyist, commercial, military), there are many interpretations in popular misuse.
This reporting system is not appropriate for rating digital signal quality. This is because digital signals have fairly consistent quality as the receiver moves away from the transmitter until reaching a threshold distance. At this threshold point, sometimes called the "digital cliff," the signal quality takes a severe drop and is lost.:38 This difference in reception reduces attempts to ascertain subjective signal quality to simply asking, "Can you hear me now?" or similar. (The only possible response is "yes"; otherwise, there is just dead air.) This sudden signal drop was also one of the primary arguments of analog proponents against moving to digital systems. However, the "five bars" displayed on many cell phones does directly correlate to the signal strength rating.
- Steven Stoker Beyond Aberdeen: A Bluejacket Diary 0595337112 2004 "Five by Five—Loud and clear (based on a system of indicating a radio's signal strength on a one to five scale)."
- Imel, Kathy J.; Hart, James W. (January 2003). "Understanding Wireless Communications in Public Safety" (PDF). FCC.gov. The National Law Enforcement and Corrections Technology Center–Rocky Mountain. Retrieved September 19, 2015.
- "ACP 131(F) - Communications Instructions Operating Signals, April 2009" (PDF). Archived from the original (PDF) on September 6, 2012.
- Ham Radio RST Signal Reporting System for CW Operation, by Charlie Bautsch, W5AM
- FM 24-6 Radio Operators Manual, US Army 1945, p17-18