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RST Explained

RST stands for Readability, Signal Strength and Tone. On CW all three codes are used for a report such as 599 which means perfectly readable, extremely strong, and perfect tone. On phone only the first two codes are used. A report might be 55 meaning perfectly readable, fairly good signals. In operation the signal strength is often taken from a reading on the S-meter.

The RST System



2--Barely readable, occasional words distinguishable.
3--Readable with considerable difficulty.
4--Readable with practically no difficulty.
5--Perfectly readable.

Signal Strength


1--Faint signals, barely perceptible.
2--Very weak signals.
3--Weak signals.
4--Fair signals.
5--Fairly good signals.
6--Good signals.
7--Moderately strong signals.
8--Strong signals.
9--Extremely strong signals.



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