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[SOLVED] Automatic Frequency Control range selection

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alexxx

alexxx

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Hi!

I would like to transmit and receive signals in the spectrum from 869.65MHz to 869.7MHz. Let's say that the tranceivers will be tuned to 869.675MHz, which is in the center of the spectrum. Now proper parameters of the tranceiver should be selected, and one of that parameter is the Automatic Frequency Control (AFC).

What is the proper value of the AFC pull-in-range?

What is this range related with? Bitrate? Frequency? Modulation?

Thanks. :)
 

if it is your project you could define anything you like. If you have to follow some standard you must read the papers. The most common technique is to divide the Rx and Tx channels. After that you know how to calculate the range. The bandwidth of each channel depended from the modulation , bitrate. Based on those parameters you have calculate the bandwidth of each channel. The result is to define the frequencies for each channel.
 
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    alexxx

    alexxx

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The AFC pull in range should compensate for the drift of the transmitters carrier frequency and the receivers local oscillator and a bit more. If the equipment is going to be manually tuned by a person who is not competent, then the pull-in range should be about 1/2 the channel width!!
frank
 
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    alexxx

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General answer is AFC needs to cover the frequency accuracy spec range of the transmitter it is receiving plus the frequency acccuracy spec range for the receiver.

For example if the transmitter has a spec of +/- 1 ppm and receiver has tolerance of +/- 20 ppm then AFC need to cover at least 21 ppm.

The process of adding AFC will often degrade the raw receiver frequency accuracy of its frequency reference circuit so the AFC range must also account for its uncertainty contribution.
 
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    alexxx

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**broken link removed**
 
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    alexxx

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Thank you guys! :smile:
 

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