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Assuming worst case,10kOhm for the
soundcard,
you had a maximum mismatch loss of
only
0,9dB,which is totally neglegible,particularly on
LF.
Sounds good!
73
Clemens
DL4RAJ
----- Original Message -----
Sent: Thursday, December 16, 2010 10:37
PM
Subject: LF: Re: Re: Re: Re: Sound Card
mic Impedance
Hi Clemens.
How about a 50 ohms in 4k out filter with
the knowlege that the sound card input Z can be anything from 4k
upwards.
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 -----
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 -----
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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