Important PLL Query

Yes, Ivan. I feel that there's a lot to learn from you. Thanks for the confirmation.

dare4444 wrote:--. Is he correct? --- Then why is he saying that? Is he confusing it with the first type comparator in CD4046? We are using the second one or PFD.

Hi,
I suppose this should continue a former discussion, which disappeared somehow. A guy argued that the concept was wrong, because the PLL could not keep full phase lock as designed. He missed, that a full phase lock is undesirable in this case. If the VCO was phase locked to the reference, the frequency modulation would be wiped out: the feedback voltage from the PLL filter would counteract the modulating voltage. Instead, you want to remove the carrier frequency drift (< 1Hz) and keep the modulation (> 20 Hz). Harry says that exactly on his pages.

VBR from Ivan

Exactly! If deviation was less than + - 75KHz then its loudness and clarity wouldn't be as good as the local FM stations or even a bit better. 

I used only one 16V zener. Best audio was obtained when loop was locked with 4.85V to 5V present on top of zener. 

I'm designing a VCO from  scratch again with a single 16V 1W zener diode biased permanently at 5V or in its linear region for distortion free audio + two back to back varactor diodes for the PLL control voltage as to not distort the RF signal and helping in spectral purity of the oscillator by keeping the varactor diodes from conducting at RF peaks. A third extra transistor preamp after oscillator and buffer section would now be added to keep the RF lightly loaded from rest of the circuit for best audio quality. 

The PLL (PFD) is no longer a mysterious entity thanks to the work of one man and his superb explanation, Harry! 

Hello Harry and Ivan, 

Still so much to learn about you. During testing I didn't measure the Kvco. Is he correct? Then I need to change the design. 

It's the same 96MHz PLL TX circuit of mine in your Transmitters section. 

Prescaler = /128

Fref = 750KHz

With the same loop filter as shown in my circuit. 

It was as loud as a commercial FM radio station during testing. Then why is he saying that? Is he confusing it with the first type comparator in CD4046? We are using the second one or PFD.