WA6HHQ:
>They are now making the dynamic range
measurements by measuring the on frequency IMD spur or blocked signal
using a narrow band spectrum analyzer. This separates the blocking or
IMD measurement from reciprocal mixing, which they will do as an
additional test.
I suppose this means no ARRL measurements will ever
again say "noise limited", but I question how practical
this is in the real world. In the latter, we want to
know when any spurious signal will cover a weak signal
at the noise floor...whether it's IMD, BDR or phase noise.
I like the term G3SJX uses (he does RSGB's Radcom product
reviews)...Spurious Free Dynamic Range (SFDR)...which
encompasses all potential sources of spurious effects.
I will note that the K3 may still have better
overall phase noise than the other rigs listed if you
integrate it over the potential bandwidth of phase noise
interference. In a typical contest situation, you may
have strong signals +/-25 kHz of your RX frequency. In
this case, phase noise from a station 25 kHz away can
still cause problems. For example, comparing to Orion:
Rig 1kHz 2 10 20 50 100 1M
K3 -110 -119 -136 -140 -143 -144 -150
ORION 2 -121 -129 -126 -125 -118 -128 -138
Delta -11 -10 +10 +15 +25 +26 +12
it is ~10 dB better at close spacings, but 10-25
dB worse at wider spacings (and over much greater
BW than the K3). Assuming you had strong signals
spaced every 1 kHz over +/-25 kHz (not unusual in
a major CW contest), the K3's *integrated* phase
noise effect could be less than Orion's. Also
I'm sure the VHF guys will love the K3's numbers,
since they are more interested in the wide-spaced
phase noise effects.
The other thing all of us need to remember about
extremely close spaced measurements is that these are
made with continuous carriers (i.e. no key clicks) from
ultra-quiet sources (e.g. HP 8640Bs or quartz oscillators).
In the real world, nearby signals will have much more
noise from clicks and their own TX phase noise. This is
why we are kidding ourselves if we think a 200-250 Hz
roofing filter will actually help much more than a 500 Hz
filter. "Theoretically" it might be better, but in the
real world of key clicks and TX phase noise, that will
far override any theoretical advantage of the narrower
filter IMHO.
Thanks for posting the data...maybe a little
worse than I had hoped for at close spacings but as I
think about it (e.g. above), it may actually yield a
better overall result for integrated phase noise effects.
73, Bill W4ZV
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