[Elecraft] KSYN3A FAQ

[Joe Subich, W4TV]

On 2015-02-13 3:15 PM, Wayne Burdick wrote:
> Another interesting issue regarding the Flex 6xxx series (and radios
> with a similar direct-digital-sampling RF architecture) is that "A/D
> Limit" descriptor in the blocking dynamic range column in Sherwood's
> chart. An ADC limit is a hard one; it does not gracefully soft-limit
> in the presence of strong signals, like an amplifier stage. Multiple
> signals in the passband can cause additive peaks that hit this ADC
> limit sooner, causing ghost signals (IMD) to appear. 3-tone (or
> higher) testing may be needed to quantify the effect of the ADC limit
> in DDC receivers. Perhaps "A/D Limit" can then be converted into a
> useful number.

In an e-mail exchange with Chen, W7AY some months ago he indicated the
"number of tones" seems to be somewhere around 10.  However, I'm sure
that is fuzzy and depends a lot on the frequency relationship and if
they are all of similar strength or there is a wide dynamic range.

Perhaps the best way to test dynamic range in direct digital sampling
receivers is noise power testing.  Run a "notched noise signal" of a
known level into the DDS receiver and increase the noise power until
the noise floor in the notch increases 1 dB.

73,

    ... Joe, W4TV



>
> Wayne
> N6KR
>
>