Hi Jim,
To quote: "If the test is designed to show response of the receiver to a lot of strong signals such as are present in a contesting or DX pileup environment, or as are present in a multi-transmitter site, the signal level should be consistent with that environment, NOT with the design of the receiver." My explanation of the optimum noise loading point was intended to clarify the test procedure. As it happens, the optimum noise loading point for an ADC is also the clipping point, which is the limiting case for a direct-sampling receiver with an ADC at RF. I state clearly in my test reports for direct-sampling SDR's that I am testing NPR just below the clip point. This hard limit dictates the maximum aggregate signal power at which the receiver can still be expected to demodulate signals correctly (assuming no attenuation is inserted ahead of the ADC). I cannot perform the test above ADC clipping, as it will then yield no usable results. In practice, some attenuation can often be inserted to extend the upper power limit of the ADC, especially on the lower HF bands where the band noise level is usually several dB above the receiver's noise floor. I have applied noise loading levels as high as -1 to 0 dBm when testing some direct-sampling SDR receivers. This is equivalent to approx. 1000 contiguous SSB voice channels, all transmitting simultaneously at S9 + 40 dB each. In the final analysis, it is up to the radio buyer to decide whether or not a direct-sampling SDR can handle his chosen operating environment. 73, Adam VA7OJ/AB4OJ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
