[Amps] Measuring IMD

[Jim Barber]

On 11/3/2013 6:53 AM, Colin Lamb wrote:
>
> A similar linearity-detecting scheme was used in a 3-1000Z design from
> the 1970 ARRL Handbook. "The SS-70 2-KW Amplifier", pp 204-208.
>
> It used diode RF detectors in the cathode and plate circuits, a
> "balance" pot and a 50-0-50 uA front-panel meter.
>
> I have no idea how well it worked, but this thread rang a bell and I had
> to go look it up. It would be interesting to try it. If the mechanical
> meter turned out to be inadequate, a connector for an external scope
> could be added.
>
> 73,
> Jim N7CXI
>
> Instead of using a meter, an led array should work fine, since the led has much faster response.  If you rectified the input and output of an amp and fed to companion led arrays, you could do the same thing as the scope.  In fact, they have solid state scopes that would work well and occupy almost no space.
>
> 73,  Colin  K7FM
>

The old National app note for the LM3914 bar graph driver shows a 
20-segment zero-center meter that drives with a +,- 5V signal. Clamping 
zeners on the detector outputs and an op-amp for buffering would make a 
fun display.

The HAL-8877 ? ;-)

73,
Jim N7CXI