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48 Threads found on Image Frequency Rejection
Dear All, Alternatively to image rejection mixers (IRM) or image filter, many wide band radios working in HF (0 to 30 MHz) band adopt the use of a 2nd or even 3rd conversion (double or triple heterodyne conversion) claimed by some folks to supress the image frequency and adjacent interferences. May be (...)
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 (...)
Why is high Q image reject filters in heterodyne receiver are lossy compared to low Q channel select filters?. Can anyone explain in detail. Thanks in advance Rgds
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 (...)
Brief answer e.g. Channel1 freq. = 900MHz Channel2 freq. = 900.025MHz Channel step = 25Khz IF = 21.4MHz Therefore VCO = 878.6MHz ( low side injection ) or VCO = 921.4MHz ( high side injection ) ACR : The ability of receiver to avoid the influrence of adjacent channel interference. e.g. Rx rece
There are a lot considerations about the IF selection, like the image rejection, the power consumption, the VCO design.. You can fist read some IEEE paper on transceiver design to get some feeling on their choices
Hi all, Do anyone know about image filter? How to design the image filter? Do anyone can share these articles or books? I search a couple of days in Internet, but cannot find the related information. Thanks in advance!
Additionally, a usual single ended mixer doesn't suppress the input frequency. So, besides the image frequency rejection problem, the IF must also be clearly separated from the received bands, that means > 285 kHz (upper LW end) and < 520 kHz (lower MW boundary).
What is an image rejection Ratio (IRR)? and How to calculate an image rejection Ratio?
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 This Part , SAFCD450 from Murata is obsolete.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 (...)
Superheterodyne receiver is known to be able to separate the image frequency from the wanted signal. However, if the interfering sources occupy exactly the same frequency as the wanted signal, how does the receiver separate them? Thank you for your comments.
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 (...)
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 (...)
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 (...)
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 (...)
For calculating the image rejection ratio in ADS, we give two signals as system input, "original signal" and the "image signal + 10Khz ". In my receiver I am down converting my signal to 20Mhz. So for calculating IRR, What i have to do ? Shall i take peek difference of "20Mhz" and "20Mhz +10Khz" or 0Hz and 10Khz? 20
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
This could be an explanation: Tuned at 780 kHz, the preselector might fail to reduce the strong 850 kHz signal sufficiently. The mixer (or any RF amplifiers ahead of it) then would get overloaded, generating the 2nd harmonic of the latter signal -- which would be at 1700 kHz. If the local oscillator runs 455 kHz above the 780 kHz frequency, t
Try this tool to select the IF .... uWaveRF - View topic - New tool added: image frequency Calculator
Here is a nice graphical representation of image frequencies, and the reason that negative frequencies are used to make the equations easier to visualize. RF Cafe - Mixer image frequency Using a higher IF will make the image frequencies to be far away from RF, which will be muc
Does a regenerative detector suffer from image signals, like direct conversion receivers? Or it just receives and amplifies only the set frequency?
Does anyone know a good supplier for general purpose hobby radio ICs like mixers, LNAs, modulators, etc.? Maybe a supplier for amateur radio hobbiests? Digikey and others only seem to sell the specialty stuff. Specifically I'm wanting to build a circuit that will downconvert a narrow-band signal from 3MHz - 30MHz to a few tens of kilohertz (say
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
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.
Sorry if I don't give a direct answer to your question. But looking at the datasheet, with an input P1dB = 10 to 14dBm (the input level at which output is 1dB lower than calculated, due to compression), and with a conversion loss = 7dB + 1dB due to compression, you can't have as high as 7dBm at IF. Second, I am not well acquainted with noise floor
Dear LvW Can you please elaborate the method. 1) I am not able to understand what you mean by by perform two anlysis , do you mean that i should do two differnt analysis while giving normal/ usual values in the first, giving the changes values in the second analysis, then compare the results of the two?? 2) About the inp
Actually the definition of the image frequency is: f_imag = f_RF + 2*f_IF in case of high side injection (LO higher than RF) and: f_imag = f_RF - 2*f_IF in case of low side injection (LO lower than RF) In case of high side injection (LO higher than RF) a Low Pass Filter can be used as an image Filter in front of the mixer, and yes in this (...)
Dear Friends, I need a solution for downconversion, I need to reject the image for low IF frequencies (about 1 MHz IF). I could not find image rejection mixer for such a low IF frequency, and so my noise figure for my entire system increases about 3 dB. Do you have any solution? Regards
The Blocker specs are all in the LTE radio level specifications, and it looks like the tables in your post have most of the details for the blocker spec. Low IF architectures have real problems with image performance, as your image frequencies tend to be a couple of channels away. It appears that all of the commercial chipsets have moved to direct
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 (...)
Why would you want to filter at RF-Band? Are you planning to make a preselection filter with CMOS? Or is it image-rejection? Then I would use an image rejection mixer. You can filter at baseband with continous-time active filter or switched capacitor filter.
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 (...)
hello lately a friend got a small gadget that is placed between the TV antenna input and the antenna , this small gadget was able to filter certain scrambled channels to display a clear image . im assuming this is a passive filter , have anyone used this before and is it a bandpass , rejection, high pass filter??? and if there is some schemat
Depends on what you are trying to accomplish. If you are looking for only modest out of band rejection, you might be ok (like with an image reject noise figure situation). If you are looking for 60 dB of out of band rejection, then yes, the non 50 ohm source will be a problem. A pad, even just 3 dB, would help. Or you could do some (...)
Thanks a lot!!! very helpful. i think i will try to find the best specifications for the single conversion, the dual conversion or Zero IF architecture. then i can define my own reasonable specification. here is my reference receiver for dual conversion: 19-mW 2.6mm2 with 8.5dB noise figures,an on-chip variable-gian channel fitler of 20dB image
IF you have double-balanced mixer, for sure, you will have teh image rejection better thatn 18dB, otherwise, you have to use sort of filter technique
Sure switched cap filter can achieve much better accuracy but they can work at lower speeds than the speeds which Gm-C filter can reach . Further more Gm-C filters are more simple and can be easily used to used to build up complex filters (for image rejection). Furthermore, the Gm-C filters can be calibrated to get acceptable accuracy in (...)
Thanks for all the helpful replies. I have some more questions: I couldn't find any single-chip direct conversoin tuner for my frequency of interest. From your suggestions I decided to use Low-IF(Quadrature Demodulation) with the same setup as mentioned in the first post. I can use an IF of 6MHz for 2Mhz channel bandwidths. I don't want to go ov
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I don't really understand what you are doing but there are techniques for multiplying two signals and not getting the image. Search for 'image rejection mixers' or something similar. Keith
I think you should take 2nd harmonic of IF frequency lower at input of mixer. It is either mixed before the input, or happend in the mixer. You can decrease 1,2,3dB for the IF power, see what happens on the image spur.
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.
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
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.
I know that the concept of negative frequencies seems to be absurd. I have been searching for the answer for quite a long time. One answer that I mostly saw was that it was because of the Euler's theorem. But now I have another reason- Here's one real negative frequency as given in Proakis- There are two waves one is 1/8 Hz and other
Hi All, I have a question about the SSB (single-side band) modulation signal, and its circuit implementation in Radio. For example, the baseband DAC has two I/Q differential signal outputs, and then they are connected to the corresponding differential amplifiers, and to the I/Q mixer (modulator). Then is the RF port of the mixer/modulator ou
Yes, you are right. If you are trying to make a very high adjacent channel rejection receiver...a zero IF or low IF are not the best choices. Chips like the ADF7023 use a low IF frequency who's actual center frequency depends on what IF filter bandwidth you choose. That somewhat optimizes things, but you are still only going to get maybe (...)