As measurements become more precise, it becomes more and more important
to recognize what Bill is pointing out. A slight difference in test
setup can result in a different result. These measurements are done at
the sub-microvolt level and it does not take much to create a difference.
Test equipment must be calibrated, and the calibration tolerance should
be known. Traceable calibration is one thing, but the tolerance limits
of that calibration are also important - not all calibration labs are equal.
Even with calibrated equipment and the same test setup, two different
equipment operators may yield two different results. As an example,
consider an instrument having a display for readout (like an
oscilloscope), the trace has a finite width, and one operator may place
the cursor on the midpoint of a trace width while another may place it
at one edge yielding two different values - how much they differ depends
on the resolution used, brightness of the trace, scale illumination, how
well the display was focused, etc.
One good step in the right direction would be to report the region of
uncertainty for all measurements. For me, that is a piece of information
that becomes more critical as the measured values become smaller. The
ARRL lab may do that calculation in-house (I haven't asked), but they do
not state it in their published reports.
So for now, when I see comparison data between two receiver that vary
only by a dB or so, I usually figure that is close enough to ignore the
difference (I usually do consider 3 dB or more difference to be
significant).
73,
Don W3FPR
Bill Tippett wrote:
snip...
It's also dangerous to assume Elecraft's measurements
will be identical to ARRL/Sherwood. There are often differences
due to different test methodologies, people and equipment.
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