definition and usage of sio codes

"Logs, or it didn't happen"

When I log shortwave broadcast receptions, I include an SIO code in my notes (such as "SIO 353"). The SIO (strength, interference, overall) code, a simplified form of the SINPO (strength, interference, atmospheric noise, propagation conditions, overall) code, is a standard way to rate shortwave reception. Each value of the code uses a scale of 1 (worst) to 5 (best), and the highest possible SIO code is 555. SIO codes are commonly included in reception reports sent by a listener to a broadcaster.

A SINPO code includes two more components but requires the listener to break strength and interference into two categories each. Shortwave listening novices (a group in which I still belong) may not know how to do this. For the sake of simplicity, I'm starting with the SIO code.

Reception reports along with SIO or SINPO codes help broadcasters understand the success of their transmissions. Transmitter sites are sometimes operated by a different organization than the broad caster, and listeners are often hundreds or thousands of miles away from broadcasters, thanks to the wonders of ionospheric propagation. So, reception reports from the broadcast target region can be very valuable to broadcasters.

Here are the three components of SIO, along with how to determine the value for a given reception:

• Strength

This rating indicates the effectiveness of the transmission for your particular location. Factors such as transmitter location, transmitter antenna direction, transmitter strength, ionospheric condition, and atmospheric attenuation can affect the strength of a broadcast. This category can be scored by evaluating the loudness of the broadcast above the noise floor, and whether any signal fading is present.

Some stations offer propagation maps that show where particular broadcasts are expected to reach. If that information is available, it can help to set your expectations about how well you might receive a transmission.

I've heard that atmospheric attenuation is better counted against the interference score, although the cause of a weak signal is not always easy to determine. North American shortwave listeners can check the latest NOAA solar data at n3kl.org. Or you can listen to the geophysical alerts on WWV or WWVH.

• Interference

This rating tells the broadcaster if there are any problems with transmitting on a particular frequency with the intention of reaching specific locations. Rather than rate the amount of locally-generated interference you receive (which the broadcaster can't control), rate the interference on the frequency itself. Same-channel or adjacent channel interference are the reasons to subtract points for this category.

If you want to factor out local interference when determining this score, try tuning to another broadcast of comparable strength within the same meter band, ideally as close to the primary frequency as possible. This can help you determine the baseline noise level. The ideal situation would be to perform your listening in a location that is largely free from radio frequency interference.

• Overall

This is your opportunity to describe the overall quality of the broadcast in spite of the signal strength or interference. This score is likely going to be in the range between the strength and interference scores, but does not need to be a simple average of the two scores. In my experience, interference is less of a factor than the signal strength, especially when the signal is fading in and out.

Some broadcasters such as Sound of Hope and Radio Marti are victims of intentional, targeted jamming. In those cases, interference plays a major role in the overall quality of the broadcast, especially if the jamming signal is louder than the desired broadcast.

If you haven't logged SIO codes before for your shortwave receptions, I'm hoping that this article gives you enough information to start doing so. I also recommend being generous in sending your reception reports to broadcasters. You may receive something in return (QSL cards, stickers, newsletters, schedules, or other gifts), stations may respond in order to provide better transmissions, and it can help ensure continued broadcasting to your area.