Re: A few useful documents

Hi Wayne,
I'm looking at the Lab Circuits at the Pi-over, and the only
thing not shown is the amount of attenuation you are getting.
I'm assuming its the 8:25, but I've forgotten how to translate
that to dB. Is it 5dB? 10*log(25/8)? Also, how does one
go about picking values for different attenuations?
On another note, from Ray Alden's book that RatShack sells, he
provides formulas for attenuation that leaves the total load
equal to the original driver. Its a series resistor and one
parallel to the driver. I suppose it wouldn't lend itself to the
HF comp. you use. Comments? I've included the perl code if anyone
cares.

Chris

./atten.pl -8
driver Z: [8.00] ohms
Series resistor: [4.82] ohms
Parallel resistor: [5.29] ohms


#!/usr/bin/perl -w

if ( ! @ARGV ) {
$drop = -6; # dB
}
else {
$drop = shift(@ARGV);
}

$driver_Z = 8; # ohms

# split the load between the driver and the resistor
$Rp = (10 ** ($drop / 20 )) * ($driver_Z/(1 - (10 ** ($drop / 20 ))));

# calc the the combined impeadance of driver and parallel
# resistor, and subtract from original Z.

$Rs = $driver_Z - ( 1 / ( ( 1/$Rp ) + (1/$driver_Z )));

printf(" driver Z: [%3.2f] ohms\n Series resistor: [%3.2f] ohms\n Parallel resistor: [%3.2f] ohms\n",$driver_Z,$Rs,$Rp);



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