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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 -----
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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