[Amps] IMD test question

[Larry Benko]

Bill,

I have made amp IMD measurements with the circuit shown at 
http://www.w0qe.com/Technical_Topics/imd_testing_of_amplifiers.html 
which can measure any amp currently made.

As I'm sure you are aware there are not any exciters made today with IMD 
in the -60dBc range.  This is why I did the test with 2 exciters.  Also 
you need to check the final input to the amp to be sure that any IMD is 
due to the amp and not the driving circuitry. An amp which has an 
impedance which varies throughout the RF cycle (any non class A amp) can 
cause the exciter to produce IMD which may improve or reduce the IMD of 
the amp.  The circuit I use can drive a 2 3CX800 amp with IMD levels 
-70dBC so that the amp IMD is easy to see.  Also theory and tests I have 
done say that the IMD doesn't change for carrier separations of 1kHz 
thru 100kHz.  In your case you might want to use 10kHz based on the 
receiver you are using.

Have fun.

73,
Larry, W0QE

On 8/1/2012 2:15 PM, Bill, W6WRT wrote:
> Is there a way for a homebrewer to accurately measure IMD without expensive
> equipment? I'm thinking of doing two-tones at full power into a dummy load while
> listening on a second RX nearby. How does one accurately analyze what one hears?
>
> 73, Bill W6WRT
>   
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