[Elecraft] Interface and Ham Radio Deluxe

[Joe Subich, W4TV]

> You can still reduce the audio from the soundcard program and,
> infact, this is what another bit of kit called the "PSK Meter"
> effectively does.

The problem with just using the sound card output level is that once
the slider gets down around 10 - where it will be if you are driving
an electret input without an attenuator - it is quite difficult to
adjust accurately.  Since a mic input designed to work with a dynamic
mic will be *another 20+ dB more sensitive* it is almost impossible to
adjust between "no audio" and "overdriving the mic preamp" with the
Windows mixer.

Remember, typical audio levels are:
   Sound card at maximum:  1.5 V RMS
   Electet mic:  75mV RMS (26 dB below sound card)
   Dynamic mic:   5mV RMS (26 dB less than electret, *50 dB* less
                  than maximum sound card level).


73,

    ... Joe, W4TV


On 10/13/2013 1:14 PM, Dave wrote:
> Without wanting to start another discussion like that on impedance
> verses radiation resistance recently, I did say "and I would always
> advise..."
>
> The isolation avoids earth loops, the variable resitor avoids
> overdriving, if you are taking the speaker output straight to the mic
> input then the PC speaker audio level can be used, but like Joe, I'd
> always prefer a system with a variable resistor external to the PC, but
> that's a personal preference.  You can still reduce the audio from the
> soundcard program and, infact, this is what another bit of kit called
> the "PSK Meter" effectively does.  http://www.ssiserver.com/info/pskmeter/
>
> Dave (GDJA)
>
> ----- Original Message ----- Sent: Sunday, October 13, 2013 12:01 PM
> Subject: Re: [Elecraft] Interface and Ham Radio Deluxe
>
>
>> An isolation transformer does not solve the excessive level problem.
>> For that you need an attenuator or voltage divider.  Typically one
>> would connect a 4.7K or 10K resistor in series between the sound card
>> output and the mic input and a 470 or 1000 Ohm resistor from the mic
>> input to the mic ground.  That 20dB is about right for the sound card
>> line/speaker output to an electret mic input.  Substitute 47K or 100K
>> for dynamic mic inputs or use a 500/1000 Ohm pot with the wiper to
>> the mic input instead of the fixed shunt resistor.
>
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