# LC filter combination for 19mhz signal

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#### LeakSt20

Hi,

Am trying to build a stereo decoder for my Leak Troughline II tuner, using the following circuit diagram at:

http://werple.net.au/~kiewavly/Leak/stereo_dec3.gif

My problem is there is no L C combination shown on the diagram. I have worked out that if I use a

1mh inductor I can use a 17.5nf cap:

If L, is 1milliHenry, then

C = 1 / ( L* ((Fo * 2 * pi )^2))
= 1 / (0.001 *( (19000 * 2 * 3.14 )^2))

but am not sure, my maths insn't great. Also could I use a 20nf cap with 20% tolerance to get the 17.8 - 22.2 nf range I need with the 1mh inductor?

Has anyone out there created this circuit? If so what combo did you use, if you used one.

I have also heard that I could use an RC filter instead of an LC filter, and this would be easier. Any help here would be appreciated.

Thanks

LeakST20

#### LeakSt20

Sorry I meant to say 19Khz not 19mhz.

#### Frank Berry

1 mH and 70 nanoFarads will resonate the circuit at 19 kHz.

#### Frank Berry

Below is a plot of the filter.

#### Attachments

• 19 khz filter.gif
8.1 KB · Views: 112

#### LeakSt20

Thanks very much Frank

#### LeakSt20

The 1mh 70nf LC filter assumes less then 1% tolerance in order to resonate at 19Khz.

The capcitor I have has is 68nf with a tolerance of 5% (anywhere from 64nf to 71nf ) and so does the 1mh choke.

Is there any way I can gurantee 19khz, perhaps using a smaller capacitor value, trimmer etc.

I appreciate any advice you can give.

leakst20

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