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In-Reply-To: <FDCC39D43D974DED978401025DB874DF@lindavideo>
References: <FDCC39D43D974DED978401025DB874DF@lindavideo>
Date: Thu, 16 Dec 2010 20:25:17 +0000
Message-ID: <AANLkTikWex1pGTvAmhyPidAHh-LbQ_XrUxHtdV=Q0Tnn@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Sound Card mic Impedance
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If its a passive L/C filter, why not do a version with unequal Zin and Zout
and take advantage of the voltage gain in going from 50ohms to, say, 500
ohms?   That will give you an apparant 10dB without trying.

AADE filter designer lets you have different termination impedances.

Andy
www.g4jnt.com




On 16 December 2010 20:06, Ken <ken.h.wright@btinternet.com> wrote:

>  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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<div>If its a=A0passive L/C filter, why not do a version with unequal Zin=
 and Zout and take advantage of the voltage gain in going from 50ohms to,=
 say, 500 ohms?=A0=A0 That will give you an apparant 10dB without trying.<=
/div>
<div>=A0</div>
<div>AADE filter designer lets you have different termination impedances.<=
/div>
<div>=A0</div>
<div>Andy</div>
<div><a href=3D"http://www.g4jnt.com/">www.g4jnt.com</a></div>
<div>=A0</div>
<div><br><br>=A0</div>
<div class=3D"gmail_quote">On 16 December 2010 20:06, Ken <span dir=3D"ltr=
">&lt;<a href=3D"mailto:ken.h.wright@btinternet.com">ken.h.wright@btintern=
et.com</a>&gt;</span> wrote:<br>
<blockquote style=3D"BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8e=
x; PADDING-LEFT: 1ex" class=3D"gmail_quote">
<div bgcolor=3D"#ffffff">
<div><font size=3D"2" face=3D"Arial">Thank you all LFs.</font></div>
<div><font size=3D"2" face=3D"Arial">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=A0 a Low Pass Filter to use with Winrad, F1, 20kHz, F2=
, 30 kHz, 100kHz -80 dB (theoretical)=A0with a characteristic impedance of=
 50 ohms, with this high input impedance=A0I can=A0locate the filter very=
 close to the sound card mic input and terminate the filter output with a=
 50 ohm resistor.=A0Hopefully this will eliminate the BC intermod I was ex=
periencing when trying to receive Chris G3XIZ the other day.</font></div>

<div>=A0</div>
<div><font size=3D"2" face=3D"Arial">73</font></div>
<div><font size=3D"2" face=3D"Arial">Ken</font></div><font color=3D"#88888=
8">
<div><font size=3D"2" face=3D"Arial">M0KHW=A0=A0 I091TV</font>=A0</div></f=
ont></div></blockquote></div><br>

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