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(Chapter 3-Continued)
When interpreting specifications (also known as "specs") on tuners the most important terms include sensitivity, alternate channel selectivity, capture ratio, separation, signal-to-noise ratio, total harmonic distortion, and frequency response.
Sensitivity is the ability of the tuner to pick up weak stations (weak stations include those that are far away and those that are behind large obstacles such as mountains or high rise buildings). Sensitivity is rated as a number such as 34 dbf, which is a good figure. The lower the number the better.
Alternate channel selectivity refers to the tuner's ability to receive a desired radio station's signal while rejecting the signal of a nearby radio station. It is rated in units of decibels (db). Unlike the spec for sensitivity, the higher the number for selectivity the better. A good figure is 75 db to 80 db.
The capture ratio of the tuner is an important specification if you live in a location between two radio stations of two different cities that broadcast on the same channel. It is the ability to "capture" or receive the strongest of the two stations. The capture ratio is also important if there are many buildings between the listener and the radio station because stray radio waves bounce off the buildings and act like they're coming from another station. For the capture ratio specification, the lower the number rating the better. A reasonable figure would be about 1.0 db, which indicates that there has to be a difference in signal strength of 1 decibel between two radio stations for the tuner to pick the stronger one.
In order to have a clear understanding of the term separation, you need to know what "stereo" means. For those readers who don't have a clear idea of stereo is, it refers to sound coming from two different sources. In other words, sounds coming from one speaker are slightly different from those coming from another. That's why we perceive the sense of depth and why we can hear different instruments from each speaker. When we're listening to any component in a stereo system sound from one channel that is meant to be heard only from that channel is unintentionally mixed into sound from the other to a certain degree. Separation is simply a measure (in decibels) of how well sounds are properly isolated to their respective channels. You must be careful when reading the spec for separation, however, because the method of measuring it varies between manufactures. Manufactures often state separation using one of several frequencies (tones): 100 Hz or 100 Hertz (a relatively low tone), 1 KHz or 1 Kilohertz (a medium-pitched tone), or 10 KHz. Chances are, the higher the frequency, the lower the separation. A good figure for separation is 25 db to 30 db at 10 KHz for the FM tuner section. Higher numbers are better.
Signal-to-noise ratio refers to how well the tuner can reduce background noise with a strong radio signal. When reading this rating there are two numbers to look at: one for "mono" (short for monophonic) and "stereo". The spec is rated in units of db (decibels). Typical figures would be 70 db and 68 db for mono and stereo, respectively, which are good. Higher numbers are better because they indicate that the reception will be marred less by noise. Stereo signals are always noisier.
