LC filter combination for 19mhz signal

LeakSt20 · 25th July 2005, 11:18 PM

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))
= 17.5 nanoFarads

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 · 26th July 2005, 08:00 AM

Sorry I meant to say 19Khz not 19mhz.

Frank Berry · 26th July 2005, 08:22 AM

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

Frank Berry · 26th July 2005, 11:06 AM

Below is a plot of the filter.

LeakSt20 · 26th July 2005, 01:29 PM

Thanks very much Frank

LeakSt20 · 8th August 2005, 02:58 PM

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

25th July 2005, 11:18 PM	#1
LeakSt20 diyAudio Member Join Date: Jul 2005 Location: London	LC filter combination for 19mhz signal 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)) = 17.5 nanoFarads 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

26th July 2005, 08:22 AM	#3
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	1 mH and 70 nanoFarads will resonate the circuit at 19 kHz. __________________ Frank

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26th July 2005, 08:00 AM	#2
LeakSt20 diyAudio Member Join Date: Jul 2005 Location: London	Sorry I meant to say 19Khz not 19mhz.

26th July 2005, 01:29 PM	#5
LeakSt20 diyAudio Member Join Date: Jul 2005 Location: London	Thanks very much Frank

8th August 2005, 02:58 PM	#6
LeakSt20 diyAudio Member Join Date: Jul 2005 Location: London	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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