[Elecraft] Sherwood Receiver Test Data - K3S Added Today

[Joe Subich, W4TV]

> In a direct-sampling receiver, how do you control the input level to
> the ADC to achieve maximum available dynamic range without clipping
> at theADC?

It's a matter of gain/attenuation before the ADC.  If, for example,
one looks at the Flex-6700 they have four steps of preamplifier gain:
0, 10, 20 and 30 dB.  The best MDS and dynamic range is with 30 dB of
gain as long as one keeps the *total input signal* below the ADC
crapping threshold.  If the total input signal exceeds the ADC crap
threshold one needs to reduce the front end gain to bring total signal
levels below the overload point but that drops the weak signals below
the noise floor (typically on a dB for dB basis as preamp gain is
reduced).

Digital processing gain (decimation) helps with the dynamic range to
some degree - e.g. dynamic range is better than the simple number of
bits - but it can't do a thing when the ADC overflows and generates
garbage data.

73,

   ... Joe, W4TV


On 11/10/2015 7:32 PM, Fred Jensen wrote:
> Question from a mathematics major [whose parents wanted him to be a EE]:
>
> In a direct-sampling receiver, how do you control the input level to the
> ADC to achieve maximum available dynamic range without clipping at the ADC?
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the Cal QSO Party 1-2 Oct 2016
> - www.cqp.org
>
> On 11/10/2015 3:58 PM, Steve Ellington wrote:
>> Looks like the K3S should be above the Flex because the Flex achieved 2DB
>> higher due to:
>>
>> Footnote Y --- "This is a testing anomaly of a direct-sampling receiver."
>>
>> Congratulations K3S
>> Steve N4LQ
>
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