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# Image Rejection Ratio (IRR)

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#### Kartik.Sulakhe

##### Newbie level 3
What is an Image Rejection Ratio (IRR)?
and How to calculate an Image Rejection Ratio?

Say you use IF1=RF-LO1, then set LO2=RF+IF1, so IF2=LO2-RF=(RF+IF1)-RF.
The difference between IF1 and IF2 is IRR.

Correct me if I'm wrong
In order to calculate an IRR, This was given to me,

A superhetrodyne receiver with an IF of 3.1 MHz is tuned to receive a carrier of 78 MHz and the radio frequency tuning stage has a Q-factor of 100. What is the Image Rejection Ratio (IRR)? Can anyone solve it for clarification?
Given,
|Vo/Vi| = 1/Sqrt [1+Q2(wo/w - w/wo)2] ----------------------- [1]

Last edited:

Hi, Kartik,

what is Q denotes? And what is the source of your equation?

Thanks.

IRR is a basically the ratio of Image Frequency Power to the Signal Power, i.e, Pim/Psig
IRR is calculated inorder to measure the amount of Amplitude and Phase mismatch in a quadrature architecture which degrades the performance of the system
IRR is basically measured in case of Hartley and Weaver image reject downconverters where in the image frequencies are rejected beyond 35dB. The mismatch can reduce the amount of rejection.

tony_lth

Points: 2