Hmmm... I just went back through my reflector mail as well as the published
Omni-VII literature, and I can't find anywhere it says 6 dB per S-unit. I
could have swore that I read that. Could be I assumed it, though... That
used to be one of the "standards" in days gone by... LONG gone by...
Just did the math based on S9 = 50 uV, and if you figure 1 uV for S0, you
get 3.775 dB per S-unit, pretty much what you said. If you use 6 dB per
S-unit, a 0.25 uV signal (nominal minimum detectable) would be between an S1
and an S2. Is this "right"? On the face of it, it doesn't seem so -- but if
you go by the old-time verbal strength descriptions for the S scale, an S1
is a "barely perceptible" signal. Neglecting any atmospheric noise floor for
the moment, a barely perceptible signal in a modern HF receiver would be
about 0.25 uV, so by these lights, maybe the 6 dB per S-unit isn't so far
off.
Maybe 5 dB makes the most sense, since this places the minimal detectable
signal near S0, and anything above that would move the S-meter (including
the atmospheric noise floor). I think that would be my vote.
Bill / W5WVO
wayne burdick wrote:
I think 3.5 to 4 dB per S-unit is closer to operator expectations,
Bill, but I'm sure TT has their reasons.
We do agree on 50 uV = S9. Whether the S-meter compensates for the
preamp and attenuator is an interesting subject; we might provide a
menu entry to turn this on/off.
73,
Wayne
N6KR
On Apr 29, 2007, at 5:15 PM, Bill W5WVO wrote:
Wayne,
Just as a data point, in case you don't know -- the Omni-VII features
a calibrated S-meter (50 uV = S9, 1 S-unit = 6 dB) on all bands, and
it always reads the same for a given signal level regardless of the
state of pre-amps or attenuators switched in/out.
---
http://www.elecraft.com
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