I'd like to know if there is an ADC that can take it's sample directly from an HF antenna and provide digital output of the amateur radio bands to a down-conversion mixer. Yes, I know it's a dumb question.
I recomend for decision of your problem ADCs with function RF (AM) detector.
Info about ADCs with function amplitude detector look on EZ (RF component,SDR receiver).
There are no dumb questions! And Yes, we have many A/D converters that can sample IF frequencies for 1-55MHz. I would suggest that you consider a new low power family of ADCs, one of which is the recently released AD9648, a dual 14 bit 125Msps ADC. . That may require quite an aggressive anti aliasing filter, so if you decide you need a higher sample rate device, consider the AD9642, a 250Msps 14 bit ADC.
Is it possible to convert the RF directly from the antenna and use DDS to tune a frequency? In other words, a direct-conversion receiver.
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