RF section
- Consists of a pre-selector and an amplifier
- Pre-selector is a broad-tuned bandpass filter with an adjustable center frequency
used to reject unwanted radio frequency and to reduce the noise bandwidth.
- RF amplifier determines the sensitivity of the receiver and a predominant factor
in determining the noise figure for the receiver.
Mixer/converter section
- Consists of a radio-frequency oscillator and a mixer.
- Choice of oscillator depends on the stability and accuracy desired.
Mixer is a nonlinear device to convert radio frequency to intermediate frequencies (i.e.
heterodyning process). The frequency conversion in the mixer stage is identical to the frequency
conversion in the modulator except that in the receiver, the frequencies are down-converted
rather that up-converted. In the mixer, RF signals are combined with the local oscillator
frequency. The local oscillator is designed such that its frequency of oscillation is always above
or below the desired RF carrier by an amount equal to the IF center frequency. Therefore the
difference of RF and oscillator frequency is always equal to the IF frequency. The adjustment for
the center frequency of the pre-selector and the local oscillator frequency are gang-tune (the two
adjustments are tied together so that single adjustment will change the center frequency of the
pre-selector and at the same time change the local oscillator). when local oscillator frequency is
tuned above the RF, we have high side injection and when local oscillator frequency is tuned
below the RF we have low side injection both Mathematically expressed as:
- Consists of a pre-selector and an amplifier
- Pre-selector is a broad-tuned bandpass filter with an adjustable center frequency
used to reject unwanted radio frequency and to reduce the noise bandwidth.
- RF amplifier determines the sensitivity of the receiver and a predominant factor
in determining the noise figure for the receiver.
Mixer/converter section
- Consists of a radio-frequency oscillator and a mixer.
- Choice of oscillator depends on the stability and accuracy desired.
Mixer is a nonlinear device to convert radio frequency to intermediate frequencies (i.e.
heterodyning process). The frequency conversion in the mixer stage is identical to the frequency
conversion in the modulator except that in the receiver, the frequencies are down-converted
rather that up-converted. In the mixer, RF signals are combined with the local oscillator
frequency. The local oscillator is designed such that its frequency of oscillation is always above
or below the desired RF carrier by an amount equal to the IF center frequency. Therefore the
difference of RF and oscillator frequency is always equal to the IF frequency. The adjustment for
the center frequency of the pre-selector and the local oscillator frequency are gang-tune (the two
adjustments are tied together so that single adjustment will change the center frequency of the
pre-selector and at the same time change the local oscillator). when local oscillator frequency is
tuned above the RF, we have high side injection and when local oscillator frequency is tuned
below the RF we have low side injection both Mathematically expressed as:
