Topband: Analog to Digital converter for 1.8MHz

[Bill Tippett]

Chuck wrote:

 >The 71.5 dB is actually S/N, not dynamic range. The Spurious Free Dynamic
Range (SFDR) is listed in the spec sheet as 90 dB which is respectable if
not top of the line.

         I believe we're mixing apples and oranges.  12-bit ADC resolution is
1 part in 4096 (2^12).  This yields 20 log (1/4096) = 72.25 dB theoretical
maximum dynamic range, without any non-linearities elsewhere and without
any auto-ranging attenuators (Rhode & Schwarz technique).  A DSP cannot
create any better dynamic range than the ADC feeding it.  Somewhere Icom
touted their 24-bit DSP as having 144 dB dynamic range (...true in theory),
but in fact both the Pro2 and 7800 both have close-spaced IMD dynamic range
numbers in the 70's.  I recall someone at Ten-Tec saying the dynamic range
of Orion's DSP (which also uses a 24-bit ADC) is in the order of 105 dB
due to system non-linearities, etc, and yet Orion's close-spaced IMD
measures in the mid-90's.

         By the way, has anyone seen measurements of the IC-7800's claimed
"110 dB dynamic range" published anywhere?  I have a feeling this is more
marketing hype from Icom...never to be measured anywhere except in their
advertising copywriter's office.  ;-)

                                                 73,  Bill  W4ZV