W3ULS:
>Can someone explain the seemingly large discrepancies between the 1993
QST transmit composite noise and the 2003 Ten-Tec phase noise graphs for
the OMNI VI?
It could simply be poor resolution of the photo
of the 1993 spectrum analyzer plot. Compare the following:
January 1993 QST Review of Omni VI, photograph on page 5...
http://www2.arrl.org/members-only/prodrev/pdf/pr9301.pdf
...to plot on p. 18 of the Omni VI+ Expanded Test Report from
1997. It looks much better even though I expect the synthesizer
designs (VI versus VI+) are basically identical.
http://www2.arrl.org/members-only/prodrev/pdf/lab/omni-6.pdf
Orion's phase noise below 2 kHz is a major contribution.
Assuming 130 dBc/Hz, and adjusting 27 dB for noise bandwidth,
this means Orion's phase noise is -103 dB at 2 kHz using a 500
Hz bandwidth filter. By comparison, both the Elecraft K2
and Icom IC-7800 had IMD that was "phase noise limited" at
2 KHz spacings using 500 Hz bandwidths. Sherwood's IMD
measurements of 80 dB at this spacing implies the phase noise
of both rigs were about 23 dB worse than Orion at 2 kHz.
http://www.sherweng.com/table.html (see footnote "f")
This also indicates why adding narrow roofing filters
alone (e.g. new Inrad for Omni VI or Yaesu MP) can only go
so far without running into phase noise limits of the basic
synthesizers. Even more amazing is that Orion holds <130
dBc/Hz down to 200 Hz spacings! This means that a very
narrow filter like the 600 Hz Inrad #762 can be used to
full advantage at extremely narrow spacings without any
degradation due to phase noise limiting.
In looking at the article, I see it was written July 21,
2004. I wonder if Ten-Tec used the time before publicly
releasing it to apply for patents? I sure hope so! This
is a REAL contribution to the state-of-the-art, unlike the
unabashed marketing HYPE coming from other manufacturers.
73, Bill W4ZV
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