[Test-Equipment] Using an HP 331A Distortion Meter

[Barry]

Thanks for the replies.  I thought the meter/analyzer has a high-impedance input so terminating the input into whatever impedance it needs to see is the primary consideration.

I was thinking of this more in the RF sense where the output of the generator needs to be terminated properly AND needs to match the input circuit (e.g. antenna, etc.) but that's not the case here with the high-impedance input.

Thanks again,
Barry - N4BUQ

----- Original Message -----
> From: "David DiGiacomo" <david at davmar.org>
> To: "Barry" <n4buq at knology.net>
> Cc: "Test Equipment" <test-equipment at mailman.qth.net>
> Sent: Tuesday, September 2, 2014 3:13:40 PM
> Subject: Re: [Test-Equipment] Using an HP 331A Distortion Meter
> 
> On Tue, Sep 2, 2014 at 2:07 PM, Barry <n4buq at knology.net> wrote:
> > I'm a bit new to using a distortion meter and have a basic question.  When
> > connecting the device I want to test to the meter's input, I assume it is
> > necessary to terminate the generator properly (e.g. into a 600-ohm
> > resistor, etc.) and that's so that the generator sees the proper load.
> >
> > What's confusing me a bit about this I may use this to measure distortion
> > for a 600-ohm-terminated signal as well as connecting it to the 8-ohm load
> > for the PA output.
> >
> > Does the meter not really care what impedance it sees on the input?  It
> > just seems odd that I would feed it a 600-ohm load in one case and an
> > 8-ohm load in another.
> 
> 
> The distortion analyzer has a high impedance input, so it doesn't care
> what the source impedance is, as long as it's not too high.
> 
> However, the distortion of the source will vary depending on how it is
> loaded, so you should connect the load that is relevant to your
> application (or if you are testing against a specification, the load
> that is specified as a test condition).
>