[Elecraft] K3 to IC-7800 Comparison?

[Jim Bolit]

Adam,
You are digging a deeper hole...........
JimW6AIM

.

-------- Original message --------
From: Adam Farson <farson at shaw.ca>
Date: 9/14/2015  6:48 PM  (GMT-06:00)
To: jim at audiosystemsgroup.com
Cc: Elecraft List <elecraft at mailman.qth.net>
Subject: [Elecraft] K3 to IC-7800 Comparison?

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



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