Topband: Analog to Digital converter for 1.8MHz

[John Kaufmann]

CHARLES HUTTON wrote:

> By the way, there are some 18 bit ADC's with spurious free dynamic range in 
> excess of 103 dB and sampling rates of over 1 MSPS. For 455 kHz IF's, they 
> would provide a fine A/D conversion that should meet even our most demanding 
> needs.

Spurious-free dynamic range has to be referenced to a measurement noise bandwidth to have any meaning because dynamic range is measured against a noise floor.  Furthermore SFDR varies nonlinearly with noise bandwidth because we are dealing with nonlinearities.  If the 103 dB SFDR is referenced to 1 Hz (which is common practice for many systems and components), then the SFDR would degrade to 63 dB when measured in a 100 Hz noise bandwidth if the dominant nonlinearity is third-order.  That 63 dB now seems less appealing as a dynamic range figure.

73, John W1FV