I must say, that of all these methods PLL seems most complicated to me. The general rule is simple and comprehensive, yes, but all the good mood is gone when we get to calculations. Do you happen to remember any books or tutorials where the designing issues are well covered and/or explained?KerimF said:The key part in a PLL demodulator (or for other functions) is the low pass filter between the phase comparator and VCO input. Also the frequency range set for the VCO affects, with the LPF, the loop response.
Your project is a very good start to let you be interested in studying how to design a PLL circuit which is one of my favourites.
So far i don't have any local oscillators. 10.7 MHz seems out of range, but it looks like 455 kHz is another popular IF. If i would like to shift it to IF, is 455 kHz much worse than 10.7 MHz?biff44 said:If you plan on changing the carrier frequency, do you have a tracking local oscillator in the receiver, so that a constant IF frequency is sent to the demodulator? If so, you might choose 10.7 MHz as the IF frequency, and upconvert the received signal to there. There are plenty of 10.7 MHz FM demodulator chips/circuits that are designed for 10.7 MHz.
Im not planning to change carrier frequency later. I can select any carrier frequency from 50kHz - 2000 kHz now, but once i make a decision, i won't be able to change it. If i would use resonant circuit it would have to be tuned only once. (btw. isn't the bandwidth too wide to use resonant circuit?)biff44 said:If you do not have a tracking LO reciever (superhetrodyne), how were you planning on retuning the discrimator resonant circuit for each new carrier frequency?
Yeah, co called Carson's rule of thumbKerimF said:Note:
For sinusoidal frequency modulation, the bandwidth required to transmit or receive the FM signal is:
BW = 2*(df + fm)
The problem with references and software for PLL is that, most often they are meant to help design frequency synthesizers or dividers.KerimF said:Now it seems there are plenty of references and even free software for designing PLL.
What about active (opamp) filters or the passive ones (R+C)?chuckey said:As KerimF said the bandwidth of your signal is 72KHz, using such a low IF as 100KHz, means that you can't use any resonant LC circuits or filters because they will lead to sideband shifts and cutting (reduction in amplitude) and hence distortion on the demodulated waveform.
Frank
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