The Collins 30L1 has such a meter in it.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Steve Thompson
> Sent: Friday, August 11, 2006 11:25 AM
> To: amps@contesting.com
> Subject: Re: [Amps] Checking for IMD
>
>
>
> Martin AA6E wrote:
>
> > 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.
> Single Sideband Principles and Circuits includes a section on
> calculating IMD from measurements of input vs output voltage. I reckon
> this will include any effects from power supply sag.
>
> For amplifiers where the transfer characteristic is linear, then going
> into gain compression it follows through to graphs of IMD against % flat
> topping on a two tone test. You can look at this by sampling the input
> and output and comparing on a X-Y display, or make two identical
> detectors and adjust the coupling so that the voltages detected on the
> input and output are identical at low level. A meter showing the
> difference will show you when non-linearity sets in. It won't be
> automatic readout of IMD to 5 digits, but if you learn how to use it, it
> will tell you most of what you need to know with voice or test modulation.
>
> As a very rough rule of thumb, don't go beyond the point where Po/Pi has
> dropped by 20% from its low level value. Don't be surprised if this less
> output than you think you should run.
>
> Steve
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