Contents
What is image suppression?
To mitigate the effects of the image spectrum, heterodyne receivers use image-reject filters. These are placed before the mixer, such that the image spectrum is suppressed before the mixer shifts it to the intermediate frequency. This is an effective solution, but there are two complications.
How can an image rejection frequency be suppressed?
To suppress the unwanted image, the tuning of the RF stage and the LO may need to “track” each other. In some cases, a narrow-band receiver can have a fixed tuned RF amplifier. In that case, only the local oscillator frequency is changed. In most cases, a receiver’s input band is wider than its IF center frequency.
How can we reject image frequency in a receiver?
6.6. Frequency translation and image frequency in a superheterodyne receiver. It is the function of the input BPF to reject the undesired image frequency. Even if there is no interfering signal on the image frequency, the noise at this frequency will get through and reduce the signal-to-noise ratio (SNR).
What is image frequency and what is image frequency rejection ratio?
The image rejection ratio, or image frequency rejection ratio, is the ratio of the intermediate-frequency (IF) signal level produced by the desired input frequency to that produced by the image frequency. The image rejection ratio is usually expressed in dB. In a good design, ratios of >60 dB are achieveable.
What is the formula of image frequency?
We insert these two frequencies into the equations and transpose the oscillator frequency: 108,5 MHz = foscillator + fIF foscillator = 108,5 MHz – f. 87,0 MHz = foscillator – fIF foscillator = 87,0 MHz + f.
Why is RF converted to if?
So a high frequency signal is converted to a lower IF for more convenient processing. The bandwidth of a filter is proportional to its center frequency. In receivers like the TRF in which the filtering is done at the incoming RF frequency, as the receiver is tuned to higher frequencies, its bandwidth increases.
What is an image rejection ratio?
Image rejection ratio. The image rejection ratio, or image frequency rejection ratio, is the ratio of the intermediate-frequency (IF) signal level produced by the desired input frequency to that produced by the image frequency. The image rejection ratio is usually expressed in dB.
What is image frequency rejection?
The image rejection ratio, or image frequency rejection ratio, is the ratio of the intermediate-frequency (IF) signal level produced by the desired input frequency to that produced by the image frequency.
What is an image reject filter?
Image rejection is typically accomplished by means of a filter that is not incorporated into an integrated circuit. In other words, image-reject filters consume PCB area and design time, and in the context of modern electronics, both of these resources are valuable and in short supply.
What is an image rejection mixer?
The Image Rejection mixer is used in specialist applications where only one mix product is needed – typically to reduce filtering. Image rejection mixers as they are sometimes known are used in a number of RF and microwave applications.