Picture response, also known as Image Response Rejection Ratio (IMRR), measures the effectiveness of a radio’s electronics in rejecting unwanted signals. It is important for minimizing interference and maintaining quality radio communications. IMRR varies with frequency and can be managed by choosing frequencies that do not interfere with intermediate frequencies. It is measured on both radio transmitters and receivers and can be compensated for by using more intermediate frequencies.
Picture response is a measure in decibels of how well the radio electronics components are working. Provides a ratio of the signals that need to pass through the radio receiver to unwanted signals. An image of a signal is generated as a result and should be rejected to minimize interference. Also called Image Response Rejection Ratio (IMRR), Image Response measures the characteristics of the signal before the Intermediate Frequency (IF) is amplified. The phenomenon is most often applied to superheterodyne radios, which use an oscillator to create two frequencies from an incoming signal; a sum and a difference of frequency.
An unwanted signal can be removed by including the appropriate circuit in a radio receiver. The circuit removes signals at a particular frequency. The other channels of the radio signal are left alone. To be effective, the nature of the image response is that the separate signals must be equal to the intermediate frequency or be twice the frequency. Otherwise, interference and pitch shift associated with receiver tuning will reduce the quality of radio communications.
The Image Response Ratio defines the level of IMRR a radio has. To get a measure of it, the desired signals and their associated image must be defined at the particular frequency on which the radio operates. Image response typically varies with frequency, and the difference between signals as a percentage is smaller as frequency increases.
Image frequency management can become complicated when antenna signals interfere with intermediate frequencies. This interference is known as an IF breakthrough. To combat this, frequencies that do not have these tendencies are usually chosen.
A radio with insufficient picture response ratio for a radio communication application will have too much interference. It will appear to have more signals than it does, which are components of the non-rejected signals. Interfering signals are not the actual frequencies your radio is tuned to, but act to reduce the quality of radio transmissions and sounds heard by radio operators and listeners.
Image response is a characteristic measured on both radio transmitters and receivers operating on the superheterodyne principle. In some cases, more intermediate frequencies are used to compensate for IMRR problems in the system. The IMRR also measures how well the radio oscillator is stabilized, including within 21st century frequency synthesizer technology and software-defined radios in computer applications.
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