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LF: Re: Re: Re: Re: Sound Card mic Impedance

To: <[email protected]>
Subject: LF: Re: Re: Re: Re: Sound Card mic Impedance
From: "Ken" <[email protected]>
Date: Thu, 16 Dec 2010 21:40:28 -0000
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Hi Clemens.
Dont forget I am trying to attenuate an unwanted incoming antenna rf voltage.
 
73.
Ken.
M0KHW 
----- Original Message -----
Sent: Thursday, December 16, 2010 9:29 PM
Subject: LF: Re: Re: Re: Sound Card mic Impedance

The 50-Ohm-termination at the output of the LP filter represents a
50-Ohm-*source* which is looking into the input impedance of the soundcard.
Hence the gross (power-)mismatch (SWR 80).
For such high impedances at vlf (=audio) frequencies
voltage matching would be much more efficient.
 
73
Clemens
DL4RAJ
 
 
----- Original Message -----
From: Ken
Sent: Thursday, December 16, 2010 10:04 PM
Subject: LF: Re: Re: Sound Card mic Impedance

Hi Clements.
Are you sure, shunting a 50 ohm resistor with 4k ohms reduces it down to 49.38 ohms or am I missing something?.
73.
Ken
M0KHW 
----- Original Message -----
Sent: Thursday, December 16, 2010 8:40 PM
Subject: LF: Re: Sound Card mic Impedance

Ken,
 
>I am doing  a Low Pass Filter to use with Winrad, F1, 20kHz, F2, 30 kHz, 100kHz -80 dB (theoretical) with a >characteristic impedance of 50 ohms, with this high input impedance I can locate the filter very close to the sound >card mic input and terminate the filter output with a 50 ohm resistor.
 
Assuming 4kOhm input impedance of the soundcard this will cause a mismatch loss
of around 13dB (95% loss) which may or may not cause concern depending of the signal level of
your antenna.
 
 
73
Clemens
DL4RAJ
----- Original Message -----
From: Ken
Sent: Thursday, December 16, 2010 9:06 PM
Subject: LF: Sound Card mic Impedance

Thank you all LFs.
Thank you for all the info that you sent me, it looks they can be anything from 4k ohms upwards, this is ok for me, I am doing  a Low Pass Filter to use with Winrad, F1, 20kHz, F2, 30 kHz, 100kHz -80 dB (theoretical) with a characteristic impedance of 50 ohms, with this high input impedance I can locate the filter very close to the sound card mic input and terminate the filter output with a 50 ohm resistor. Hopefully this will eliminate the BC intermod I was experiencing when trying to receive Chris G3XIZ the other day.
 
73
Ken
M0KHW   I091TV 
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