[AMPS] 2 tone intermod test

[measures]

> John,
>
>I have not been paying much attention to this discussion but I did have 
>this thought about generating and measurment of two tone using a computer 
>with a sound card. 
>
>There are a lot of people using sound cards these days. They seem to be 
>doing marvelous things with them.
>
>It seems to me that a sound card could generate the two tones (or more) 
>quite easily and I beleive with a very good fidelity (low harmonics etc,). 
>This could provide a test signal into a transmitter/amplifier that is 
>being evaluated.

And you still would not have a simulation that matched the actual 
situation.  The only alternate generator is an Afican gray parrot. 
>
>Another receiver might be used for the reception of the transmitter under 
>test and it's audio (with no agc and some calibration) 

or the use of a 1db step-attentenuator method

>used to demodulate 
>the transmitted signal with the audio output going to the input of a sound 
>card/computer. The sound card would detect the two tones and even tune the 
>receiver (most ham transceivers these days have computer control) to sweep 
>the frequency to measure the two primary tones and the intermod products 
>to provide a performance measurement of the transmitter under test. 
>
>The test receiver might use a narrow band filter and tune for the sum and 
>difference products. I obvious am no expert on this but it seem 
>interesting. Has this been done? Where are the holes in this idea and what 
>might be done to plug them?

The adjacent channels test for measuring total IMD requires knowledge of 
the skirt selectivity of the test Rx to assure that it is tuned just 
beyone the fundamental window.  The optimum place to measure products 
from a LSB signal is roughly 3.8KHz up.  The optimum place to measure a 
USB signal is approx. 3.8 KHz down.  

cheers, Harry

-  Rich..., 805.386.3734, www.vcnet.com/measures.  


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