[Amps] Checking for IMD

[Martin AA6E]

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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