How to Evaluate a Reception

In the early years of wireless telegraphy, abbreviations were created to accelerate the communication process. One of the most frequently used abbreviation types was the Q-code, represented by three letters. It was used to express with brevity and clearness a question or an answer. For example, the operator on the transmitter station sends the prefix QRT?, that means "shall I stop sending?". The corresponding answer of the operator in the receiver station was with the prefix QRT, that means "stop sending".

From the Q-code the radio amateurs have been created your own code, the so-called RST-code, an abbreviation of the main characteristics of a received signal: "Readability", "Signal Strenght" and "Tone". Each letter assumes a numeric value, that varies from '1' to '5' for R, and from '1' to '9' for S and T. The meaning of each value is indicated below. Remember that the tone is applied only for continuous wave (CW) transmissions, not being applicable for radiophony. This code is also used for evaluate utility transmissions.


`Readability`

`1`	`-`	`Unreadable.`
`2`	`-`	`Barely readable, occasional words distinguable.`
`3`	`-`	`Readable with considerable difficult.`
`4`	`-`	`Readable with practically no difficult.`
`5`	`-`	`Perfect 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`	`-`	`Moderated strong signals.`
`8`	`-`	`Strong signals.`
`9`	`-`	`Extremely strong signals.`

`Tone`

`1`	`-`	`Extremely rough hissing note.`
`2`	`-`	`Very rough a.c. note, no trace of musicality.`
`3`	`-`	`Rough low - pitched a.c. note, slightly musical.`
`4`	`-`	`Rather rough a.c. note, moderated musical.`
`5`	`-`	`Musically modulated note.`
`6`	`-`	`Modulated note, slight trace of whistle.`
`7`	`-`	`Near d.c. note, smooth ripple.`
`8`	`-`	`Good d.c. note, just a trace of ripple.`
`9`	`-`	`Purest d.c. note.`

In the beginning of the 60's, it was introducted a new code from the SFL code created by the BBC, that was called SINPO-code, composed of five estimation criteria to evaluate the reception quality. The name SINPO is the abbreviation of five words, each one representing a criterion, and varying from '1' to '5': "Signal Strenght", "Interference", "Noise", "Propagation Conditions", "Overall Merit". These criteria have its own equivalences in the Q-code, as will be seen later. The information about the reception quality when using this code is done by applying the following scale:

`scale`	`S`	`I`	`N`	`P`	`O`
`5`	`Excellent`	`Nil`	`Nil`	`Nil`	`Excellent`
`4`	`Good`	`Slight`	`Slight`	`Slight disturbance`	`Good`
`3`	`Fair`	`Moderate`	`Moderate`	`Moderately disturbed`	`Fair`
`2`	`Poor`	`Severe`	`Severe`	`Severe disturbance`	`Poor`
`1`	`Barely audible`	`Extremely strong`	`Extremely strong`	`Very poor propagation`	`Useless`

The information related to this code should be given with the word SINPO being followed by the ratings (for example: SINPO 35343). Below, a brief explanation about each criterion:

S (signal strengt): the standard for the S-value should be a local radio station. If the signal received from the shortwave station has the same volume as the local station, it is marked with '5'. If, even with the volume control turned to maximum, the shortwave station is almost not undestandable, it is marked with '1'. The S-meter contained in many communications receivers should be very useful. The corresponding Q-code is the prefix "QSA".
I (interference): the disturbances caused by other radio stations, either voluntary or involuntary. The voluntary interference in most cases has political reasons. A example is the jamming. Involuntary interference occurs when a station superimposes another. In this case, either the stations are transmitting in the same frequency (co-channel interference) or transmitting in adjacent frequencies (adjacent channel interference). If the interference exists, it should be indicated in the reception report the station that interfers and its corresponding frequency. The value '1' should be attributed to an interference which renders the program unintelligible. if there are no interferences at all, the value '5' should be given. The corresponding Q-code is the prefix "QRM".
N (noise): the noise can be natural (static) or artificial (caused by electrical or electronic equipment, transmission lines, fluorescent lamps, etc). If there is no noise, the value '5' is given; but, if there is very much noise, the value '1' is given. The corresponding Q-code is the prefix "QRN".
P (propagation perturbances): This criterion refers to the signal oscillations due to fading. If there are no oscillations, the value '5' should be given. On the other hand, if the influence of the fading increases the value attributed to P decreases, as shown below:
- '5': no fading.
- '4': less than 5 fades per minute.
- '3': from 5 to 10 fades per minute.
- '2': from 10 to 20 fades per minute.
- '1': more than 20 fades per minute.
The corresponding Q-code is the prefix "QSB".
O (overall merit): this is the overall evaluation of the transmission. Generally, it is dependent on the four criteria above. The corresponding Q-code is the prefix "QRK".

Despite of these defined criteria, the SINPO-code is very subjective. For example, a listener can evaluate a transmission as "32232", while another listener can evaluate the same transmission as "44333". In addition, a beginner listener can have difficult in rating for the criteria N and P accurately. So, some stations adopt a simplified form of the SINPO-code, the so-called SIO-code, where the criteria N and P aren't used. For example, a evaluation by using the SIO-code should be given as "SIO 333".

The SINPO-code can be indicated also as SINFO; the difference is the letter F (that means Fading), instead of the letter P.