Signal strength and readability report

Introduction
A readability and signal strength report is a standardized numerical report format for reporting to another radio station the strength radio signal and the readability (quality) of the voice of their transmission as received at your location and by your radio station equipment. The report consists of two digits, each ranging from 1 to 5, resulting in 25 possible combinations. The best possible signal report is five by five. 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.

The move to plain-language radio communications means this format is now considered obsolete, to be replaced by plain language radio checks, which avoid the ambiguity of which number stands for which type of report and whether a 1 is considered good or bad.

Radiotelephony report format
This reporting system is usable with, but perhaps not completely 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. 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.

CCB signal strength and readability
The 1943–1945 Combined Communications Board Publications, including CCBP 3-2, describe a slightly newer format of the U.S. Army FM 24-6 procedure:"a) A station is understood to have good readability unless otherwise notified. Strength of signals and readability will not be exchanged unless one station cannot clearly hear another station.""b) The response to 'How do you hear me?' will be a short concise report of actual reception such as 'Weak but readable,' 'Strong but distorted,' 'Loud and clear,' 'Strength Four,' etc."At least in CCBP 3-2, no additional detail is given about what the range of the numeric scale is, or the complete list of strength and readability code words are.

FM 24-6 Radiotelegraph signal report format
The 1945 U.S. Army Radio Operator's Manual, FM 24-6 defines the radiotelegraph signal report format as follows:

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."