Frequency Demodulation with CD 4046

[chineerat]

Hello!

I am doing a project which involves frequency demodulation, I am using
the CD 4046. I have connected it in frequency demodulation
configuration. However my ouput and at any carrier frequency I am
gettting a triangular waveform at less than 20mV and at about the 10 -
100 Khz frequency.

Also my demodulated signal "rides" on that signal, therefore my signal
is noisy.

Are there any troubleshooting techniques any of you guys can give me.
THANKS!!!

 

[Luhan Monat]

chineerat wrote:

Hello!

I am doing a project which involves frequency demodulation, I am using
the CD 4046. I have connected it in frequency demodulation
configuration. However my ouput and at any carrier frequency I am
gettting a triangular waveform at less than 20mV and at about the 10 -
100 Khz frequency.

Also my demodulated signal "rides" on that signal, therefore my signal
is noisy.

Are there any troubleshooting techniques any of you guys can give me.
THANKS!!!

Hi,

It help if you posted a schematic with circuit values, frequencies, etc.

--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
http://members.cox.net/berniekm

 

[Rich Grise]

On Sun, 06 Mar 2005 19:32:11 -0800, chineerat wrote:

Hello!

I am doing a project which involves frequency demodulation, I am using
the CD 4046. I have connected it in frequency demodulation
configuration. However my ouput and at any carrier frequency I am
gettting a triangular waveform at less than 20mV and at about the 10 -
100 Khz frequency.

Also my demodulated signal "rides" on that signal, therefore my signal
is noisy.

Are there any troubleshooting techniques any of you guys can give me.
THANKS!!!

It's hunting. What you're seeing is the loop trying to lock in. One
of the guys who knows about poles and zeros can answer this in a heartbeat.

But, as Luhan Monat has said, a schematic and all the information would
be very helpful.

Good Luck!
Rich

 

[Andrew Holme]

chineerat wrote:

Hello!

I am doing a project which involves frequency demodulation, I am
using
the CD 4046. I have connected it in frequency demodulation
configuration. However my ouput and at any carrier frequency I am
gettting a triangular waveform at less than 20mV and at about the 10
-
100 Khz frequency.

Also my demodulated signal "rides" on that signal, therefore my
signal
is noisy.

Sounds like your loop is unstable. That triangular waveform is a tell
tale sign. I bet it just gets worse if you try to use a bigger loop
filter capacitor! You need to do the loop design properly. There's a
worked example in Art of Electronics.

 

[Michael Black]

chineerat (gaz_it_up@yahoo.com) writes:

Hello!

I am doing a project which involves frequency demodulation, I am using
the CD 4046. I have connected it in frequency demodulation
configuration. However my ouput and at any carrier frequency I am
gettting a triangular waveform at less than 20mV and at about the 10 -
100 Khz frequency.

Also my demodulated signal "rides" on that signal, therefore my signal
is noisy.

Are there any troubleshooting techniques any of you guys can give me.
THANKS!!!

Do you know how these work? There is a phase detector and a voltage
controlled oscillator. The phase detector compares the incoming signal
with the output of the VCO, and outputs a signal which feeds the
voltage control input of the VCO to get the VCO on that frequency.

If the input signal is just a fixed frequency, the DC output of
the phase detector will be relatively constant, minuse noise that
needs to be filtered out.

Change the input frequency, and that DC output will vary after
you get the noise filtered out.

Frequency modulate the input frequency, and that DC output will vary with
the modulation, but it is that output from the phase detector that
is the recovered modulating signal.

If the filter at the output of the phase detector is not right,
you won't be able to recover the modulating signal from the 4046.

Michael