Explanation of the Sinfo - Sio code

As soon as reception reports started flowing into radio stations, some kind of internationally recognized codes were introduced. These were needed not only to standardize report writing, but to be able to compare one report with another. The first, and most popular was the SINPO code, in which each letter stands for a specific item, and each is rated from 1 to 5. Full details are given below.

S-Signal

I-Interference

N- Natural Noise

P-Propagation Conditions

Overall merit

5-Excellent

5-None

5-None

5-Excellent

5-Excellent

4-Good

4-Slight

4-Slight

4-Slight disturbance

4-Good

3-Fair

3-Moderate

 3-Moderate

3-Moderately disturbed

3-Fair

2-Poor

2-Severe

2-Severe

2-Severe disturbance

2-Poor

1-Barely Audible

 1-Extremely strong

1-Extremely strong

1-Very poor propagation

1-Useless

Whilst the above may look impressive as well as concise, it will soon become evident that the SINPO code is very subjective. Somebody may rate a signal as 33232 whilst someone else might rate it as 44333. Likewise, although the original SINPO code did lay down technical specifications for each number (i.e. a number 3 in the P column meant a fixed number of fades per minute) these are hardly ever adhered to by reporters. Nor is it advisable to use the so called 'Signal Strength' meter to judge signal strength. No 'S' meter on a communications receiver under US $600 in price is anything more than a tuning indicator. The 'S' meter reading is usually dependent on the setting of the RF gain control, so use your ears, not the needle, to judge signal strength. You may also find references to the "SINFO" code in some literature. In this case the 'F' stands for Fading, instead of 'P' for Propagation, but the two codes are essentially the same.

It is also clear that many listeners cannot distinguish between the 'I' which stands for man-made interference, the 'N' which stands for natural atmospheric noise, and the rating for 'Propagation' is not often understood. There are some books and periodicals that maintain the SINPO code as being the only one for DX reporters. However, from a station's point of view we suggest the following, simpler, code which is used by most professional monitoring stations around the world.

The SIO Code

S-Signal Strength

I- Interference
(of any type)

O-Overall merit

5-Excellent

5-No interference

5-Excellent

4-Good

4-Nil or very slight

4-Good

3-Fair

3-Moderate

3-Fair

2-Poor

2-Heavy

2-Poor

1-Useless

1-Extreme

 1-Unusable!

You can see that the SIO code is based on the SINPO code, but in a simpler form. The use of the SIO code, as opposed to the SINPO code, does not give the station the impression that you are an inferior reporter.

 

The Backward Secret to the SIO code!
Most books that cover the subject of reception report writing have a very simple method of evaluating a signal. First, they say, judge the signal strength, then look at the level of interference. Finally, fill in the 'O' column by taking the average of the two numbers, and rounding down to the nearest whole number. So if the 'S' was 3, and the 'I' was 4, the 'O' rating would automatically be '3'. This is very misleading!

Instead, you should work backwards. First evaluate the overall rating of the signal. Is it 'listenable' or difficult to hear? Give it either 1, 2, 3, 4 or 5. Now examine the reasons for your 'O' rating. The signal may be weak (i.e. a 2) but if there is no interference on the signal, you simply have to turn up the volume control to enjoy the program. Thus an SIO rating of 244 is not impossible.

Likewise a signal of 442 is possible. This might occur if the signal was strong, there was no interference, but the audio being broadcast was heavily distorted due to a fault in the transmitter. Listen around on the bands, and you will find a wide variation in the audio quality being broadcast. Being critical may alert a station to a problem. It is often very difficult to judge when measurements are made at the transmitter site.

If you give an 'Interference' rating of either 1, 2 or 3 in your report, then you should explain why (as our example does in the 'Technical Remarks' column). If there is interference on the received signal, note the following details:

  1. Is the interference signal of the same frequency (so-called co-channel?). If it is, then as you move the tuning knob, the signal you want, and the interfering signal, will be tuned out together. If, however, the interference get stronger as you tune either up or down the band, the interference is probably coming from an adjacent frequency. It helps to indicate whether the interference is coming from a station on a higher or lower frequency than the one you are interested in. For example, if you are listening on 9895 kHz and a station on 9890 kHz is causing interference, the interference is from a station which is lower in frequency. In the interference station is a jamming signal (a buzzing sound designed to deliberately interfere with an international broadcaster) then this should be noted too. Fortunately, jamming levels on shortwave have dropped considerably in the last few years, except in Asia and the Middle East.
  2. Local weather conditions do not generally affect shortwave broadcasts, with the exception of local thunder storms in your area. These may cause loud 'crashes' which spoil reception. If this affects your 'I' (Interference) rating, then note elsewhere that this was due to local thunderstorms.