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19 Threads found on Image Frequency Rejection
There are two reasons: 1. For Real IF or High IF the image frequency have tigther rejection requirements for most systems. So you need additional filtering in RF 2. The integrated channel filter operate at much lower frequency for Zero IF. Otherwise it must use also an external IF filter. So both are finally cost/space (...)
In a multiple conversion receiver each mixer (or mixing process) would have its own image frequency, whatever is the 1st, the 2nd, or the 3rd in the chain. An image filter placed in the front of a mixer will suppress the image signal AND the image noise. Usually the 1st mixer use at its input (RF input) an (...)
To design this image filter, very important is the frequency spacing between RF and LO signal, which is the IF frequency. If the IF frequency is very low compared to RF frequency, would be a challenge to design an image reject filter with 40dB rejection.
A high first IF makes it easier to get good image rejection but is more difficult to get narrow bandwidth. A dual conversion receiver starts with a high first IF then converts it down to a lower frequency where it's bandwidth can be more easily tailored. Brian.
MOve to RF design Forum. A radio such as this needs to tune BPF of RF channel with ganged LO so that image rejection is applied. 11.5MHz LO will mic 12MHz and 11MHz into 0.5MHz. so RF experts prefer to mix such a broad spectrum into 2 stage conversion unless you have good RF ganged tuneable filter. Wide tuner radios are much different. What sensit
Do not confuse Sideband Suppression with image rejection. Direct Conversion Receivers doesn't have an image frequency. In an IQ receiver, ideally the I and Q channels of the radio signal carry orthogonal, non-interfering, channels of information. Mismatch (imbalance) in the Gain or Phase of the I and Q channels results in (...)
I am not sure these arguments are entirely correct. The image is 2xIF from the desired frequency for one thing. For the FM band of 88-108MHz the image is not even in the band (which may be why an IF >10MHz was chosen). Also, there is some front end selectivity to provide image rejection. Keith
Usually, the first IF in a double heterodyne receiver is selected according to image rejection requirements and available input filter specifications. ADC parameters may matter in a digital receiver. All in all, there's too little information.
Hello there, I have designed a 450-458MHz saw filter into my pager as a means of image frequency rejection and also as a means of preventing the Local Oscillator reaching the Antennae. This Part , SAFCD450 from Murata is obsolete. Does anyone have any other ideas where I should be looking for a replacement or can anyone recommend any (...)
Thanks for the help, Another question: Can an image rejection Mixer also be used as an Single Sideband Upconverter if there are no filters and the frequency ranges are right ? Also, if I have a situation like this: I want to downconvert a signal from RF = 20 GHz to IF = 1 GHz. The LO is supposed to be at 21 GHz. I am cert
In general an image filter is a standard Band Pass Filter. Because the duty of the image filter is not only to filter the image frequency and also reducing the image noise, the bandwidth of this filter shall be equal with the RX bandwidth. The out of band rejection of the (...)
In low-IF, I/Q mismatch causes the degradation of the image rejection. Since the adjacent channel is the image frequency in low-if receiver if 1/2 bandwidth is choosen as low-if frequency, if I/Q mismatch(SSB, gain/phase imbalance in quadrature mixer) is -30dB and the adjacent channel is +30dB higher than (...)
You are avoiding two problems. image response has two aspects. One is the selectivity of the system before the mixer. The second is the presence of high power signals that may be at the image frequency. The usual advice for image rejection is to have the IF at least 10-20% of the RF. The more (...)
You can certainly do this, but it's not really practical. To get a fully modulated signal, you need to have the DAC output at an IF frequency. Now you are faced with dealing with image rejection in your transmit chain, which makes the design more complicated. To increase the DAC output frequency high enough to make the (...)
PXF analysis is intended to give an indication of different gain vs product indexes, while PSS is the most accurate one. For example you can use PXF to see if there is image rejection or if you want to know how large can be an unwanted output frequency out of the non linear circuit under evaluation. With PSS you ussually perform all (...)
Are you sure your IF frequency is high enough? With an IF of 28MHz, your image band is within your desired band. For instance, if the desired is 16.700GHz, then the LO is 16.728GHz, but the image is 16.756GHz which is still in band. You will have to have very good image rejection to supress this, not (...)
Hi, It may depend on how far the image frequency is from the needed frequency: the closer the image to the receive frequency the more demanding it becomes to meet image rejection vs receive pass band frequency, isn't it? Please be more specific on the (...)
Hi all, let's say I have an heterodyne front-end. The first mixer will bring both the signal and noise at image freq on the IF freq. This will lead to a ~3dB NF degradation and thus an image rejection filter is required (for other reasons also...). Next comes an IQ demodulator which rejects the image (...)
If the RF input is a real signal then using a complex mixer with I and Q you get a complex IF output with both frequency ranges. Then you could apply a image rejection filter. It is called polyphase filter. It could reject the unwanted image to some degree. If you have a complex RF and a complex LO you mix down to IF a (...)