# Finding the Demodulator value

Discussion in 'The Projects Forum' started by goldfish300, Nov 29, 2009.

1. ### goldfish300 Thread Starter Member

Mar 12, 2009
12
0
hey

i would like to as a question about some kind of issue about finding the value "x" that is shown the fig below , well the value of the Freq. should be 96Khz which is the value i need to reach and this is by passing some stages to reach only the value of the freq. =96Khz (thats mean removing all the previous Freq. and voltages and only keeping the last value of Freq =96Khz in order to have the analogue graph . so i'll post what stages i must pass in order to reach that point that iv tried but still can't figure out . if someone know plz help as soon as u can .

here is the pic of the circuit that i attached in the post for those who can help me

and the stages that must pass through this circuit must look like that

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2. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
Your post makes no sense to me.

3. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
Actually, it makes sense to me.

You have 4 signals being summed:
50Hz 220v
10kHz, 10v
20KHz, 5v
X kHz, 10v
One way to approach it would be to use three very narrow band-reject filters in series; one for 50Hz, one for 10kHz, and one for 20kHz.
Another way would be to subtract the known frequencies in subsequent sum modules, eg: instead of summing the signal with 50Hz 220v the second time, sum it with 50Hz -220v, which should be 180º out of phase with the original 50Hz 220v.

Oops, OK, I posted without really looking at the 2nd part of the question very hard.

The 1st high-pass filter can get rid of most of the low-frequency stuff.

I don't know what you mean by a high-pass filter with same frequency carrier. Are you trying to say an IF section?

An LC tank acts as an open circuit to it's resonant frequency, and as a short to ground to frequencies other than resonant.

I guess this is homework, but you don't know where to start, right?

Last edited: Nov 30, 2009
4. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
One of the things that confused me was the title.