Examcrazy Logo
MBA in India CAT How to Prepare for Exams Technical Freshers Jobs
  Follow us|  twitter  Orkut  facebook
Electronics II Tutorials
   Overview Analog Wireless Communcation
   Resistors, Capacitors, RC Networks
   Diodes, Amplitute Modulation, Diode Detection
   RL Circuits, Inductive Kicks, Diode Snubbers
   RC filters. Series resonance and quality factor, Matching, Soldering
   Ladder filters Butterworth and Chebyshev filters Filter tables ADS
   Bandpass ladder filters Quartz crystals
   Impedance inverter
   Ideal Transformers
   Transformer shunt inductance
   BJT-Large signal models
   Transistor switches. Voltage regulators
   Transistor switches. Voltage regulators
   Common emitter amplifier. Max. efficiency of class A amps. Transformer coupled loads
   Available power. Distortion. Emitter degeneration. Miller effect
   Emitter follower and differential amplifiers
   JFET Source follower amplifier
   Oscillators. Clapp oscillator. VFO startup
   Variable frequency oscillator. Gain limiting
   Receiver incremental tuning. Crystal oscillators
   Mixers. Gilbert cell
   Superheterodyne receivers. Spurious responses of mixers
   Decreasing channel bandwidth by using CW
   Audio amplifiers
   JFETs as variable resistors
   Automatic gain control
   Noise, SNR, MDS, noise power density and NEP
   Nyquist noise formula. Cascading noisy components. Noise figure
   Receiver intermodulation and dynamic range
Other Electronics 1 Tutorials
   Diode Tutorials
   BJT Tutorials
   MOSFET Tutorials
   Applied Electromagnetics Tutorials
Free Electronics Tutorials
   Diode Tutorials
   BJT Tutorials
   MOSFET Tutorials
   Electronics II Tutorials
   Applied Electromagnetics Tutorials
   Microwave Tutorials
GATE preparation tips
   GATE Books & How to prepare
   Objective Solving Tricks
   Other GATE links
   IES exam preparation
   All about DRDO-SET
More Engineering Links
   Directory of coaching Institutes
   Govt engg college rankings
   Private engg college rankings
   Admission notifications for Mtech/PhD
   All Engineering Colleges in India
Superheterodyne Receivers Spurious Responses of Mixers

Superheterodyne Receivers Spurious Responses of Mixers
Recall from that a direct conversion receiver has the following simplified system diagram:

The frequencies internal to the direct conversion receiver are:

From the last lecture, we can now understand that while f+ and fare the intended output signals, other frequency components will also be present at the mixer output due to HO harmonics produced in the mixing process. As we’ll see shortly, these HO harmonics are not the same as “spurious responses of the receiver”, known as “spurs.” The superheterodyne receiver does not have the same troubles with image frequencies as the direct conversion receiver does:

The frequencies internal to the superheterodyne receiver are:
Stage 1:

Stage 2:

in the text, the NorCal 40A system diagram is:

Spurious Responses of Receivers (Spurs)
In addition to the image frequencies, there are additional spurious output responses from the receiver (called “spurs”) caused by signals mixing with higher harmonics of the LO. By definition, a spur is an unintended output signal from a receiver. For example, the VFO and BFO images shown in the diagrams on page 2 are spurs.
Recall that in the Gilbert cell, the LO (or more precisely a square wave at the LO frequency) multiplies the RF signal in the time domain.
This process will inevitably produce spurs due to the presence of HO harmonics produced by mixing. Let’s consider these HO spurs from the RF mixer. In this case:

We ask: What RF frequencies can mix (i.e., multiply) with the third harmonic of the LO (VFO) to produce an output at the frequency fif? Mathematically, we are asking:
f3 ? =3flo +fif
or rearranging,
f3 ? =3flo ?fif
If a received antenna signal is present at this frequency f3? , we will hear it at the same time we hear the intended signal at frfNot good. So once again, we need to filter this spur out.The other third harmonic spur is located at the frequency
So, spurs at f3 ? and f3 ? are in fact the “image frequencies” of the third harmonic of the LO. To verify that these two frequencies can generate spurious responses from the receiver, consider the following:
• For f 3?–

So indeed, we see a signal at f3 ? would generate a spurious signal at fiffrom the RF mixer.
• For 3 f ?–

Again, we see that a signal at f3 ? would generate a spurious signal at fif from the RF mixer. There are also possible spurs from higher-order mixer products:

and so on.
How many and which spurs are potentially troublesome for a receiver depend on the specific construction of the receiver (its IF, RF, VFO, etc.)Let’s look closely at the NorCal 40A and identify the troublesome spurs.
1. VFO image:
Fi = fif ? flo = 4.9 ? 2.1= 2.8 MHz

2. Third VFO harmonic spurs:
(This spur is in the AM radio frequency band.)

The RF Filter does a good job of filtering out both of these third harmonic spurs. However, f 3? can be very strong and consequently heard on occasion.
3. Fifth VFO harmonic spurs:
f5? =5flo ?fif =5?2.1 ?4.9 =5.6MHz
f5? =5flo +fif =5.2.1+ 4.9=15.4MHz

Of all the spurs, it turns out that f5 ? is the one closest to the intended RF signal. It causes the largest spurious response in the NorCal 40A since it is difficult to filter out while at the same time continuing to receive the intended RF signal. In Prob. 28, you will work to locate two of the strongest spurs in the NorCal 40A, both of which are related to the RF Mixer. These are the image frequency fi of the RF Mixer and the fifth VFO-harmonic spur f5 ? of the RF Mixer.
Later in Prob. 29, you will locate and measure the dB reduction of f3 ? from the RF Mixer. However, you will be measuring the output voltage from the Product Detector. Consequently, what you are actually measuring is how much of this RF Mixer spur “bleeds through” the Product Detector.

Discuss about MOSFET here
Discussion Board for MOSFET
You can discuss all your issues on MOSFET here
Thread / Thread Starter Last Post Replies Views
fourier transform
plz send me the notes for fourier transforms its very urgent.

Posted By :-
Aug 31, 12:14:03 PM 0 68766
Fourier Transform
Sir I want tutorial on Fourier Transform.........

Posted By :-
Jul 15, 3:24:49 PM 0 72255
fourier transform
sir i want tutorial on fourier transform

Posted By :-
Jul 11, 10:08:19 AM 0 68027
match filter
heloo sir ,i want a tutorial for match filter.plz send it as soon as possible it is very urgent.

Posted By :-
Jun 4, 2:25:18 AM 0 89718
Electic circuits
I want lecture notes for single phase ac & 3phase ac circuits

Posted By :-
May 21, 11:32:46 AM 1 115811
electro statics
what is the work done to move a charge? derive an expression for assembling a configuration of point charges

Posted By :-
May 12, 8:28:18 AM 0 68196
electromagnetic waves
i want lcr circiut teorems derivations

Posted By :-
May 12, 8:23:58 AM 0 66957
i want oscillator frequency derivations for all. plz let me know from where i can get that

Posted By :-
May 4, 5:21:01 PM 0 68464
Equivalent circuit Models
I've got a question in one of my revision papers,

Explain the advantages of representing a transistor by means of an equivalent circuit circuit model

The only thing i can remember is that you can take complex circuits and break them down into simpler circuits which are easier to understand,

Is this the only advantage or do you have any more?

Please help!

Posted By :-
Apr 12, 6:33:57 PM 2 148016
temperature Vs reverse satuation current
I want to know the variation of reverse saturation current with the increase in temperature for both germanium and silicon diodes

Posted By :-
Jan 28, 7:17:23 PM 0 74085
communication system
analog and digital communication system, fiber optic communication, telecommunication technique and application, mobile communication

Posted By :-
Dec 17, 10:38:27 AM 0 80387

Posted By :-
Dec 14, 3:29:22 PM 0 80782
coaching in ies in indore
what about coaching

Posted By :-
Dec 7, 5:27:52 PM 0 85027

To start your new thread you must login here.
New user signup at ExamCrazy.com Exam Crazy
To reply/post a comment you need to login, Use your user name and password to login if you are already registered else register here

(Members Login)

  About us | Privacy Policy | Terms and Conditions | Contact us | Email: support@Examcrazy.com  
Copyright © 2014 Extreme Testing House, India. All rights reserved.  662