W5WVO:
>I don't know what the test configuration of the SDR-5000 was -- I
don't think
it uses any discrete hardware roofing filters, does it? -- but Elecraft is
already claiming that the IMDDR3 at 5 kHz spacing (400 Hz CW roofing filter)
will be greater than 100 dB. (See K3 Specs page) I don't believe Eric would
have let that spec be on a public web page unless he was pretty certain it
would still be true when the final numbers come out. :-)
The QSD design of the SDR-1000/5000 is completely different than
that used by the Orion/K3, so it does not need roofing filters. Specs
like IMD/BDR are determined by the resolution and linearity of the ADC
in the sound card. Although Sherwood did not publish 2 kHz
measurements, he did say the IMD/BDR performance is basically
independent of signal spacing, so 2 kHz IMD performance is
likely 96 dB also. BDR at 100 kHz was measured at 123 dB,
which will also likely apply at 2 kHz.
Phase noise was reported as:
Phase noise (normalized) at 10 kHz spacing: 123 (flat) dBc *
* Phase noise does not fall off at 6 dB per octave as expected. Flex
believes the present phase noise limitations are caused by A/D clock jitter.
By contrast the K3's phase noise is:
Rig 1kHz 2 10 20 50 100 1M
K3 -110 -119 -136 -140 -143 -144 -150
Bottom line is that QSD-based SDRs are very different beasts, so
our assumptions based on classical designs are probably wrong.
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. For
example Ten-Tec maintains Orion's 5 kHz IMD spec is "101 dB typical",
but nobody else has ever measured more than about 95 dB, so I
would wait for independent measurements on the K3.
73, Bill W4ZV
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