[K3CAL] RST CODE

[David Hardy]

Maybe you all knew this already, but I learned a bit from this article.  I'm condensing a copy for my ham shack.
The RST code is used by amateur radio operators, shortwave listeners, and other radio hobbyists to exchange information about the quality of a radio signal being received. The code is a three digit number, with one digit each for conveying an assessment of the signal’s readability, strength, and tone. The code was developed in the early 20th century and was in widespread use by 1912.
Readability
The R stands for “Readability”. Readability is a qualitative assessment of how easy or difficult it is to correctly copy the information being sent during the transmission. In a Morse code telegraphy transmission, readability refers to how easy or difficult it is to distinguish each of the characters in the text of the message being sent; in a voice transmission, readability refers to how easy or difficult it is for each spoken word to be understood correctly. Readability is measured on a scale of 1 to 5.

Unreadable
Barely readable, occasional words distinguishable
Readable with considerable difficulty
Readable with practically no difficulty
Perfectly readable

Strength
 
The S stands for “Strength”. Strength is an assessment of how powerful the received signal is at the receiving location. Although an accurate signal strength meter can determine a quantitative value for signal strength, in practice this portion of the RST code is a qualitative assessment, often made based on the S meter of the radio receiver at the location of signal reception. “Strength” is measured on a scale of 1 to 9.[1]

Faint signal, barely perceptible
Very weak
Weak
Fair
Fairly good
Good
Moderately strong
Strong
Very strong signals

For a quantitative assessment, quality HF receivers are calibrated so that S9 on the S-meter corresponds to a signal of 50 μV at the antenna terminal. On VHF and UHF receivers used for weak signal communications, S9 often corresponds to 5 μV at the antenna terminal.
Tone
 
The T stands for “Tone”. Tone is only used in Morse code and digital transmissions and is therefore omitted during voice operations. With modern transmitter technology, imperfections in the quality of the transmitter modulation that can be detected by humans are rare. Tone is measured on a scale of 1 to 9.

Sixty cycle a.c or less, very rough and broad
Very rough a.c., very harsh and broad
Rough a.c. tone, rectified but not filtered
Rough note, some trace of filtering
Filtered rectified a.c. but strongly ripple-modulated
Filtered tone, definite trace of ripple modulation
Near pure tone, trace of ripple modulation
Near perfect tone, slight trace of modulation
Perfect tone, no trace of ripple or modulation of any kind










Variations
 
An example RST report for a voice transmission is “59”, usually pronounced “five nine” or “five by nine”, a report that indicates a perfectly readable and very strong signal. Exceptionally strong signals are designated by the quantitative number of decibels, in excess of “S9”, displayed on the receiver’s S meter. Example: “Your signal is 30 dB over S9.”
Suffixes were historically added to indicate other signal properties, and might be sent as “599K”:

X: stable frequency (crystal control)
C: “chirp” (frequency shift when keying)
K: key clicks

Because the N character in Morse code requires less time to send than the 9, during amateur radio contests where the competing amateur radio stations are all using Morse code, the nines in the RST are typically abbreviated to N to read 5NN. In general, this practice is referred to as abbreviated or “cut” numbers.


David Hardy      
davehardy0101 at aol.com
    
KB3RAN
 
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