G8B02 If a receiver mixes a 13.800 MHz VFO with a 14.255 MHz received signal to produce a 455 kHz intermediate frequency (IF) signal, what type of interference will a 13.345 MHz signal produce in the receiver?
A. Quadrature noise
B. Image response
C. Mixer interference
D. Intermediate interference
- The mixer stage in a receiver combines the input signal with an oscillator signal to produce the sum and the difference of the two signals. Filters or mixer design will select the desired new signal. known as the intermediate frequency (IF) signal. In this case the input signal is 14.255 MHz and the oscillator signal is 13.800 MHz. The sum of these two signals is 28.055 MHz andthe difference, which is used as the intermediate frequency, is 0.455 MHz or 455 kHz. These signals are then passed through a filter to eliminate the unwanted frequencies leaving only the desired intermediate frequency of 455 kHz.A signal at 13.455 MHz, when subtracted from the 13.800 MHz oscillator signal will also produce the 455 kHz intermediate frequency. (See Figure G8-7) When an undesired input signal also produces
- a signal at the intermediate frequency, the resulting interference is called image response interference. One way to reduce image response interference is to use an input filter that allows signals in the desired receive frequency range to pass through, but blocks signals outside of that range.