FIGURE 1 shows the block diagram of a superhetrodyne radio receiver. In a test a 20 uV signal was fed from the aerial into the first stage of the receiver, a radio frequency amplifier. This signal is the passed through several stages of the receiver to eventually appear at the input to the AM detector. For the AM detector to work satisfactory it requires a minimum signal level of ─3dB(mW). Calculate the required minimum gain of the fifth intermediate amplifier given the data in TABLE 1.
First we need to convert the input voltage level quoted as a voltage amplitude in uV to a power level.
V_in = 20uV = 2 10^-5V
This is equivalent to an input amplitude level in dBuV given by
V_in(dBuV) = 20Log(V_in(uV)/1uV) = 20Log(20/1)
V_in(dBuV) = 26dBuV
We can convert this to an equivalent power level in the required units of dB(mW) also written using the conversion
P_in(dB(mW) = V_in(dBuV) - 108.75dB = 26dBuV - ...
The minimum gain of intermediate amplifierin superhet radio receiver are examined.