[Amps] Checking for IMD

[Bill Fuqua]

An oscillator, good mixer and a sound card running FFT should work. You 
want to mix the RF down to around 10 kHz ( center of the sound card 
frequency range) and observe sidebands around it.

You can use a sound card to also produce the two tone test signal to insert 
into the SSB exciter.

73
Bill wa4lav



At 10:43 AM 8/11/2006 -0400, Martin AA6E wrote:
>Bill,
>
>I've wondered about this, too.  The lab method is to use a high-priced
>spectrum analyzer, but couldn't you do something useful with a soundcard
>based spectrum analyzer?  You would need to have a linear detector and a
>two-tone audio source.  This would be similar to the IMD measurement you
>get with a PSK31 monitor.  The trouble is you need pretty good dynamic
>range to measure a healthy system.
>
>You could check the boxes being sold by www.cleanrf.com as described in
>the latest CQ.  They let you look at "linearity" on a scope.  My take is
>that you will only catch gross non-linearity (overdrive), but you
>wouldn't get quantitative IMD numbers with this approach.
>
>73 Martin AA6E
>
>Bill Turner wrote:
> > Is there a simple procedure one can use for checking the IMD of an
> > amplifier? Frankly, it's something I have never tested myself, instead
> > just keeping the amp tuned correctly and underdriving when using SSB.
> > I've never gotten any complaints of splatter so I think it's under
> > control. Since I do mostly RTTY and some CW it has not been an issue
> > but I would like to be able to check it.
> >
> > Any recommended reading on the issue?
> >
> > Bill, W6WRT
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