[Elecraft] K3 to IC-7800 Comparison?

[Wes (N7WS)]

Seems to me that he's just trying to explain himself.

On 9/15/2015 6:04 AM, Jim Bolit wrote:
> 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
>
>
>