SINPO, acronym for signal, interference, noise, propagation, and overall, is a code used to describe the quality of radio transmissions, especially in reception reports written by shortwave listeners. Each letter of the code stands for a specific factor of the signal, and each item is graded on a 1 to 5 scale (where 1 stands for very bad and 5 for very good). The code originated with the CCIR (a predecessor to the ITU-R) in 1951, and was widely used by BBC shortwave listeners to submit signal reports, with many going so far as to mail audio recordings to the BBC's offices.
The use of the SINPO code is subjective and varies from person to person. Not all shortwave listeners are conversant with the SINPO code and prefer using plain language instead.
- S (Signal strength)
- The relative strength of the transmission.
- I (Interference)
- Interference from other stations on the same or adjacent frequencies.
- N (Noise)
- The amount of atmospheric or man-made noise.
- P (Propagation)
- Whether the signal is steady or fades from time to time.
- O (Overall merit)
- An overall score for the listening experience under these conditions.
Examples of SINPO code applied
In responding to a shortwave reception, the SINPO indicates to the transmitting station the overall quality of the reception.
The SINPO code in normal use consists of the 5 rating numbers listed without the letters, as in the examples below:
54555 - This indicates a relatively clear reception, with only slight interference; however, nothing that would significantly degrade the listening experience.
33434 - This indicates a signal which is moderately strong, but has more interference, and therefore deterioration of the received signal.
Generally, a SINPO with a code number starting with a 2 or lower would not be worth reporting, unless there is no noise, interference or loss of propagation, since it would be likely the signal would be unintelligible. This does not apply to shortwave stations broadcasting on SSB, however, as there is no carrier signal to receive.
One shortwave listener (SWL) may rate a signal as 33232 while another SWL at a different location might rate it as 44333. Although the original SINPO code established technical specifications for each number (i.e., a number 3 in the P column meant a fixed number of fades per minute), these are rarely adhered to by reporters. The 'S' meter displays the relative strength of the received RF signal in decibels; however, this should not be used as the sole indication of signal strength, as no two S meters are calibrated exactly alike, and many lower-priced receivers omit the S meter altogether. References to a "SINFO" code may also be found in some literature. In this case, the 'F' stands for Fading, instead of 'P' for Propagation, but the two codes are interchangeable. It was presumed that the average listener would be more familiar with the meaning of "fading" than "propagation".
Some listeners may not be able to distinguish between the 'I' which indicates interference from adjacent stations, and the 'N' which describes natural atmospheric or man-made noise; also for some listeners, the rating for 'Propagation' may not be completely understood. Various books and periodicals maintain the original SINPO code as being the only one for DX reporters. However, many stations suggest the SIO code -- a simpler code which is used by most professional monitoring stations around the world.
- "BBC Engineering Division Monnograph, Number 43: September 1962".
- Reception Reports: Reporting Code - Writing Useful Reception Reports http://www.dxinginfo.com/dx-reception-reports-codes.html[dead link]