Okay thank you. I don't know well what values you want; I took what was
advised in the motorola application note
loop damping factor = 0,707
VCO gain = 25 132 741 rad/V
VCO center frequency = 77 MHz
PLL supply voltage = 5V
etc.

The values of the components of the filter are given in a previous post.


"zindazenda" a écrit dans le message de news:
...
and your filter values Damien?
i use those pll chips myself in various tx's..6.25khz to 100khz steps and
have no problems so will dig out the values for 6.25khz for you tonight to
compare.(using LF351/(6) (i think) as filter.
also pll built on double sided pcb (1w exciter.)
no seperate screening apart from vco coil,vco regulated with 78L08,( which
also supplies the 145152) noise is not a problem.sounds like as you
suspect
really bad vco overshoot.

Woohoo ! I finally found, I had used 92 ohms resistors instead of 92 Kohms
resistors... how inattentive I am sometimes ;-) But it isn't yet perfect,
I've took a picture of the oscilloscope, showing the output signal that is
fed into the VCO (http://www.mcarsweb.com/_divers/oscillo.jpg the vertical
scale is enlarged). It is slightly varying, at a frequency of about 187 KHz.
I don't know if I should change the filter values, or add a additional small
filter, with a resistor and a capacitor between the output and the ground.
What do you think about that ?

Damien

Woohoo ! I finally found, I had used 92 ohms resistors instead of 92 Kohms
resistors... how inattentive I am sometimes ;-) But it isn't yet perfect,
I've took a picture of the oscilloscope, showing the output signal that is
fed into the VCO (http://www.mcarsweb.com/_divers/oscillo.jpg the vertical
scale is enlarged). It is slightly varying, at a frequency of about 187 KHz.
I don't know if I should change the filter values, or add a additional small
filter, with a resistor and a capacitor between the output and the ground.
What do you think about that ?

Damien

Well, you're not locked. Did you measure the gain of theVCO? In other words,
did you disconnect the tuning diode from the PLL and then plot the VCO's
output frequency versus tuning voltage? You need this data to accurately
calculate the loop components. Another item to look for is the Vcc supplu
rails to the PLL and VCO. These need to be clean. Did you do a good job of
de-coupling the supply to the PLL?

Regards,

KD0QO

"Damien Teney" wrote in message
...
Hello all,
I 've built PLL in order to command the VCO of a VHF receiver.
Unfortunately
it doesn't work very well: the VCO output is on average equal the same as
the frequency programmed in the PLL, but it is constantly varying a bit
around it. I guess the problem comes from the output filter, but I've
re-calculated it and it should be okay. Where could the problem come from
??

FYI, the PLL is build from a schematic of the Motorola application note
980

(http://www.mcarsweb.com/_divers/sche...cation-note_98
0.gif).

Thank you in advance for your answers ;-)

Well, you're not locked. Did you measure the gain of theVCO? In other words,
did you disconnect the tuning diode from the PLL and then plot the VCO's
output frequency versus tuning voltage? You need this data to accurately
calculate the loop components. Another item to look for is the Vcc supplu
rails to the PLL and VCO. These need to be clean. Did you do a good job of
de-coupling the supply to the PLL?

Regards,

KD0QO

"Damien Teney" wrote in message
...
Hello all,
I 've built PLL in order to command the VCO of a VHF receiver.
Unfortunately
it doesn't work very well: the VCO output is on average equal the same as
the frequency programmed in the PLL, but it is constantly varying a bit
around it. I guess the problem comes from the output filter, but I've
re-calculated it and it should be okay. Where could the problem come from
??

FYI, the PLL is build from a schematic of the Motorola application note
980

(http://www.mcarsweb.com/_divers/sche...cation-note_98
0.gif).

Thank you in advance for your answers ;-)