[sdiy] VCA signal analysis

Phil Macphail phil.macphail at liivatera.com
Mon Dec 9 14:23:52 CET 2013

On 9 Dec 2013, at 15:05, "cheater00 ." <cheater00 at gmail.com> wrote:
>> But definitively a notch filter.  And not that hard to make:
>> http://www.moorepage.net/Twin-T.html
> How do you measure the distortion introduced by the self-made notch filter?

By connecting the output of the notch filter to the distortion analyser. 

>> Or, as you  say, just get an audio analyser and be done with it:
>> http://www.milton.arachsys.com/nj71/index.php?menu=2&submenu=8#analysers
>> Yes, it is bigger, and not quite as good as an AP, but then if you
>> hunt around you can pick up a used one for less than the price of a
>> new MOTU 828 Mk 3, and its inputs will handle several hundred volts
>> (you can hear the relays clicking as it autoranges), and it is built
>> like a tank.  And other than the control and GPIB part, it is
>> all-analogue :)
> ...and with 70 dB dynamic range perfect for testing the fidelity of
> transatlantic phone lines :-)

With the fundamental attenuated by the notch the dynamic range is increased, it's a standard technique in test equipment.

> Cheers,
> D.
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