3. The expression Pn2/G indicates the relative noise contribution and gain of an amplifier. This expression is
the equivalent noise temperature of the receiver (Te).
4. The first step in arriving at Te is to determine the noise figure. The noise figure of a receiver is obtained by
measuring the noise power. Once the noise figure has been obtained, conversion to equivalent noise
temperature may be performed.
5. The equivalent noise temperature is obtained by rearranging the noise figure expression.
F = 1 + Pn2
GPn1
Pn1 (F -1) = Pn2 = Te (equivalent noise temperature)
G
290(F - 1) = Te (in degrees Kelvin)
LEARNING EVENT 11: FACTOR METHOD OF DETERMINING NOISE CONTRIBUTION
1. A simplified method of determining the relative noise contribution of a receiver is in current use. This
method is known as the Y factor method. This method does not use complex devices or calculations.
2. The Y factor method provides a means of determining the relative noisiness of a receiver on a day-to-day
basis. The Y factor of a receiver cannot be compared with the Y factor of another type of receiver without
introducing constants and subsequent calculations.
3. The Y factor of a receiver is defined as the receiver's noise power output with a matched source (290€ K)
input divided by the noise power output without the noise source supplied.
Y = Pn2 + Pn1 when
Pn1 = matched source noise power,
Pn2
and
Pn2 = receiver noise
4. The Y factor may be expressed in terms of a ratio or in decibels. It is usually expressed in term of decibels.
To express the Y factor in decibels, use the formula-
Y = 10 log
Pn2 + Pn1
DB
Pn2
3-9
SS0031
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