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Working of Phase loop lock......................

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koolguy

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Hi,

In PLL the phase sensor is used how it work, as the i/p freq. is matched with Vco variable oscillator??
 
A delay line.
 
Disregard that post, apparently I wasn't paying attention when I posted it =) The Wikipedi page for phase detector covers things pretty well.
 
Hi,

mixer are used for changing freq. of a signal, as in divider circuit the freq. is divided by any n no. but how to multiple freq. in real how does it work?? please elaborate this for brtter understanding as i have seen this in my comm. course book.


Thanks.
 
i have seen this in my comm. course book.
You should read the explanation there, That will give you more details than you can get
in bits and pieces from several forum members. No one here has time to type what is equilvalent to a whole chapter in your textbook.
 
You should read the explanation there, That will give you more details than you can get
in bits and pieces from several forum members. No one here has time to type what is equilvalent to a whole chapter in your textbook.

Ok, i was Reading this Introduction to Mixers, but don't understand use of if?? please tell use of it.
 
A mixer, BLENDS two or more signals.

If you have a square-wave, and a sine-wave, you can put them through a mixer and the result will be 1 signal with the square-wave ontop of the sine-wave.
 
A mixer, BLENDS two or more signals.

If you have a square-wave, and a sine-wave, you can put them through a mixer and the result will be 1 signal with the square-wave ontop of the sine-wave.


It mixes the s/g @ what freq. if the input are @ diff. freq.??
& What does IF do??
 
Hello,

After going to long reading i have one question, why local oscillator freq. is higher than RF freq. in superheterodyne receivers??
 
It could be higher or lower, not sure why higher is more common.
 
A mixer, BLENDS two or more signals.

If you have a square-wave, and a sine-wave, you can put them through a mixer and the result will be 1 signal with the square-wave ontop of the sine-wave.
An adder would give you a square-wave riding on top of a sine-wave. A mixer is a non-linear device which performs a multiplication to give the sum and difference of the two frequencies, not just the original signals on top of each other.
 
The local oscillator frequency can be above or below the signal frequency.
The IF frequency can be above or below the oscillator frequency.

Now consider a simple AM broadcast receiver, this probably has an IF of 470khz and receives signals in the ranges 150 to 285 khz (the long wave band) and 530 to 1600khz (the medium wave band).

In the long wave case the local oscillator could tune from 320 (470-150) to 185 (470-285)khz. If you calculate this out throughout the range of frequencies, you will see that when trying to recieve 235 khz, the local oscillator is on 235 khz.
Not a good situation for a receiving an intelligible signal, the local oscillator will be much stronger than the received signal and prevent it from being heard.

Now, if the local oscillator is set to be above the signal frequency, it will run from 620 (150+470) to 755 (285+470)khz, and at no point will the local oscillator be on the same frequency as the required signal.

The same applies to the medium wave frequencies, try calculating it out.


However, if we have a fixed frequency VHF receiver tuned to 156Mhz, with an IF of 10.7Mhz, the local oscillator can be on 166.7Mhz (156+10.7) or 145.3Mhz (156-10.7).
Either frequency will work no problem.

JimB
 
Hi,

can you tell how to find local oscillator in circuit or give a fig. of it??
As we change high freq. to low freq. in this process how can the message signal will not effected??

& The IF for FM should be constant always 10.7MHz
 
Last edited:
can you tell how to find local oscillator in circuit or give a fig. of it??
Read a book or look on the internet how a superhet receiver works.
Understand the block diagram and the corresponding circuit diagram.
Study basic circuits, amplifiers and oscillators.

As we change high freq. to low freq. in this process how can the message signal will not effected??
Because the side frequencies and amplitudes with respect to the carrier are maintained through the mixing process.

The IF for FM should be constant always 10.7MHz
The IF frequecny can be whatever the circuit designer decides.
10.7Mhz is a "standard" as is 21.4Mhz, filters and transformers are commonly available for these frequencies.

JimB
 
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