A television minimum signal varies with model and mainly depends on the TV receiver Noise Figure (NF) and minimum Signal-to-Noise (S/N) ratio. The lower the NF and the lower the minimum S/N, the better the reception. Both NF and S/N are commonly measured on a decibels (dB) base 10 logarithmic scale (see Tech section / dB Scale).
System noise figure is a measure of the noise a receiver contributes to the signal. It is the noise power ratio between input and output. Television receivers typically have a noise figure of 10 dB, but it can be as low as 6 dB, to as high as 15 dB or more.
Minimum Signal to Noise Ratio
The Signal to Noise ratio is the difference between signal power and noise power (signal / noise). A TV receiver will typically have a minimum S/N of 30 dB, some claim as low as or lower than 20 dB. In real world conditions interference from signal multi-path, other transmissions, and nearby electronic sources, effectively increases minimum S/N to 30 dB.
|Noise Figure||10 dB||6 to 15 dB|
|Signal to Noise||30 dB||20 to 35 dB|
Background noise, also called thermal or kTB noise, is based on Boltzmann's Constant constant (k), receiver noise bandwidth (B), and temperature (T). An RF channel noise bandwidth is 6 MHz. Temperature has a very minor effect, and it's standard practice to use 290°K (62°F) or 300°K (80°F) for calculations. The receiver noise floor is -106 dBm.
Signal and noise power are measured in dBm -- decibels (dB's) above or below 1 milliwatt (see Tech section / dBm Signal Power) .
TV RECEIVER SIGNAL LEVELS
Published Minimum Signal
Published minimum signal is usually a measurement made under ideal conditions in a quite noise free RF shielded cage using a clean test signal. Some sources state minimum signal as -83 dBm.
Actual Minimum Signal
Most television require a minimum signal of -65 dBm, but it can be as low as -75 dBm to as high as -55 dBm. A minimum signal of -65 dBm is based on estimating real world noise interference from other transmissions and any near-by electrical and electronic sources.
Signals greater than -5 dBm will saturate (overwhelm) the receiver distorting the signal so it cannot be processed.
|Low S/N||< -65||---|
|Minimal||-65 to -55||0 - 17%|
|Normal||-55 to -45||17 - 33%|
|Good||-45 to -30||33 - 58%|
|Strong||-30 to -5||58 - 100%|
TV MINIMUM SIGNAL POWER
Most TV's and locations will |
require a signal of ≥ -65 dBm.
Pmin = kTB (NF) (S/N)
kTB Noise (80°F)
Estimate TV Minimum Signal
Television Minimum Signal