First of all, the ARRL is showing (as you note) transmitted phase noise. Rob
lists receiver phase noise. Ideally, they should be the same, but are they really?
Second, there can be significant test sample variation and variation between
phase noise test sets.*
Third, phase noise measurements aren't trivial. Witness the dozens of
application notes and articles dealing with the subject. ARRL's own Test
Procedures Manual states: " *NOTE: Composite noise setup is very sensitive to
environment noise. Use of common-mode ferrite chokes may be required if test
fixture problems are encountered as described in the procedure for this test."
In my working career I have seldom seen or made, a phase noise plot that wasn't
corrupted by 60Hz spurs, for example.
* Rob himself summarizes this on his website:
http://www.sherweng.com/images/MeasurementAccuracy&SampleVariation.pdf
And last, but certainly not least, why get bent out of shape over one number.
Rob does at once a service and disservice by publishing his charts. They are
extremely handy but too many people jump on one number to rate (rank) equipment
and totally disregard things like ergonomics (If they didn't the K3 would be at
the bottom of the list). He recognizes this in his closing paragraph of the
above referenced work. We should pay it more heed.
Wes N7WS
On 4/2/2014 10:09 AM, dave wrote:
Why does the ARRL lab test show the KX3 TX phase noise as about -124 dBc/Hz
(Fig 5 of their report) and Sherwood show this as -144 dBc/Hz, both at 10 kHz
spacing? That is a huge difference.
The ARRL report shows that the KX3 never goes below about -135 dBc/Hz, even 1
MHz away.
Is there an update to the ARRL lab test? Did the ARRL miss this one?
FWIW, ARRL shows the K3 at about -142 and the FTdx5000 at -135, at 10 kHz
spacing.
73 de dave
ab9ca/4
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