Purpose of Monitoring

Trans World Radio has monitors who send in up-to-date information on reception conditions in our various target areas. The objective is to confirm that propagation is following in the predicted trends and to notify us of interference with our signal.

S I N P O Code

A code has been devised to produce a concise and easily understood Monitoring report. This is known as the SINPO code.

	Signal Strength	Interference	Noise	Propagation	Overall Merit
5	Excellent	Excellent	Excellent	Excellent	Excellent
4	Good	Good	Good	Good	Good
3	Fair	Fair	Fair	Fair	Fair
2	Poor	Poor	Poor	Poor	Poor
1	Just Audible	Extreme	Extreme	Extreme	Extreme

Signal Strength

Receivers equipped with a meter give a comparative indication of signal strength. When monitoring with a receiver that doesn’t have an S meter, it is advisable to use a known strong station, (such as a nearby medium wave station or the strongest shortwave station as a standard, having a grade of 5.) The main point is to be consistent. When the signal strength has been unchanged it is important to record the same grade on each report.

Interference

This is not to be confused with noise, which will be explained later. There are three kinds of interference.

When a station is operating on or near the same frequency it produces what is known as (heterodyne) interference. The mixing (or more correctly, the beating) of two radiowaves produces an audio signal. Most often this is a high pitched whistle, but it can become lower pitched when the interfering station is transmitting on nearly the same frequency.

When an adjacent station is very strong or their transmitter is poorly adjusted, audio from their signal can cause interference. This (splatter) interference is most pronounced when the offending station is playing music.

When a station is used to deliberately transmit noise, this is called (jamming). This interference often spreads across a wide portion of the band. The adverse affects created by the jammer can spread many thousands of kilometers beyond the intended target area

Noise

There are two types of noise to be considered.

Atmospheric static. This type of noise comes chiefly from thunder clouds. To a much lesser extent the sun and other celestial bodies produce noise.

Man made disturbances. These noises are produced by electrical appliances, such as electric motors, car ignition and high voltage electrical distribution lines. Generally, the sourcde of noise is Of a local nature and can vary greatly from day to day.

One point to remember is that a strong signal will cause your receiver to become less sensitive to noise.

Propagation (Fading)

This relates the stability of the strength of the received signal. Shortwave reception depends on the reflections of the radio waves from the ionosphere. Conditions are constantly varying. For a given target area the best frequency may not be the one predicted for that particular time and season. The result can be severe fading, distortion or little or no received signal.

There is normally some fading as the radio wave follows different paths to the receiver. As we approach the maximum usable frequency, fading will stop. It is undesirable to operate close to the maximum usable frequency since just the slightest change in propagation could cause the signal to disappear. “Multi-path” distortion affects the sound by canceling some audio frequencies while at the same time causing others to be dominant. The signal may also “flutter” at times creating an unnatural sound.

Overall Merit

This is related to the transmissin as a whole. That is, was it pleasant listening? Could it be easily understood? I have found it is easiest To choose the overall merit first, then I decide which of the other factors are responsible for my selection of that overall rating.