[hpsdr] LTC2208 input network design

[Mark Haun]

Hi Jeff,

On 09/26/2012 08:22 PM, jeff millar wa1hco wrote:
> An LC simply rolls off faster than an RC and so does a bit better at
> limiting buffer output noise outside the band of interest.

Makes sense--thanks.

On a related note, if I understand correctly, at least one DDC HF receiver
(QS1R) does not use a differential amplifier/driver at the ADC input, opting
instead to keep all of the gain/attenuation blocks further back (on the
other side of the balun/transformer?), where they are more easily swappable
for undersampling applications.  At least, this is what I gather from my
google searching--I am sure someone here will correct me if I am wrong.

Browsing Linear's latest and greatest differential ADC drivers, I see one
(LTC6409) which appears to equal or beat the LTC6400-20 in distortion and
noise performance, while being quite broadband (~400 MHz at 20-dB gain).  I
wonder if it would be possible to come up with an input topology based on
this, which would use pluggable LPF/BPF modules between the amp and ADC,
allowing one select a Nyquist zone?

73,

Mark KJ6PC

 1348808702.0