Jim brings up a very good point that most folks seem to overlook.
That is "............ design seems to "only" realize some 18 or maybe 19
bits of "effective" A/D conversion as just over 100 dB dynamic range is
suggested by Doug as what is being realized in tests. Even if 32 bit A/D
chips were available, it does not mean that that much resolution of the
analog conversion would occur. "
State-of-the-art 24-bit IF-DSP converters, such as those used in the Ten-Tec
Orion, produce about 100 dB of dynamic range.
73
Bob, K4TAX
----- Original Message -----
From: "Jim Reid" <jimr.reid@verizon.net>
To: "Robert & Linda McGraw K4TAX" <RMcGraw@blomand.net>;
<tentec@contesting.com>
Sent: Monday, December 30, 2002 3:25 PM
Subject: [TenTec] Orion vs. Jupiter Audio vs. DSP
> Was written:
>
> > The dynamic range of a digital system is based on the number
> > of binary bits in each word.
>
> > Each bit corresponds to a doubling of the resolution,
> > or roughly 6dB of dynamic range capability. Telephone systems
> > typically use 8 bits which is approximately 48 dB dynamic range
> > linear, although effectively more when companded. Today's CD's
> > and most digital recorders use a 16 bit system for some 96 dB of
> > dynamic range.
>
> A couple of lines written by Doug Smith about the A/D conversion
> within the coming Ten Tec Orion rig:
>
> "State-of-the-art 24-bit IF-DSP converters, such as those used in
> the Ten-Tec Orion, produce about 100 dB of dynamic range.
>
> (Note: the theoretical resolution with 24 bits, is 144 dB!)
>
> That
> means a receiver can handle signals from the noise floor to almost
> 40 dB over S9 without analog AGC. Above that level, analog AGC
> is still necessary to maintain the linearity of analog circuits and to
> prevent overload in the ADC hardware.
>
> Do not be misled by hype about 32- and 64-bit processing. In a
> correctly executed design, it is mainly the dynamic range of the
> ADC hardware that determines how a receiver will perform in the
> presence of crushing QRM.
>
> 32-bit ADCs with enough speed and accuracy to handle IF-DSP do
> not yet exist and 24-bit resolution is the best available."
>
> And 24 bit chips for A/D are used within the Orion design, state-of
> the-art A/D chips, per Doug's piece, see:
>
> http://www.doug-smith.net/dspdynamics.htm
>
> However, even Doug's design seems to "only" realize some
> 18 or maybe 19 bits of "effective" A/D conversion as just over
> 100 dB dynamic range is suggested by Doug as what is being
> realized in tests. Even if 32 bit A/D chips were available, it
> does not mean that that much resolution of the analog conversion
> would occur. Important is also the decision made in the
> conversion when the amplitude, for example, is "between" sample steps;
> does it round up or round down, hi. Lots of little details besides
> just the spec claims about the chips themselves.
>
> Whatever, Doug's design, as promised, is the "best" promised
> in the amateur rig market so far; we will see in a few weeks
> what will actually be delivered and experienced by Orion users.
>
> 73, Jim KH7M
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