[Discuss-gnuradio] Interleaved sampling without interleaved clocks?

[madengr]

Posting this to GR (as opposed to USRP) since it seems more theory.

Say I have an X300 and want to get DC - 200 MHz BW from a single daughter
card by combining two real sampled streams.  The X300 ADCs (or within the
dual channel ADCs themselves) clocks can't be interleaved.

An argument is that one of the two RF input channels can simply be delayed
90 degrees with a length of coax.  This gives 90 degree shift at 200 MHz, 45
at 100 MHz, etc, with the argument being the lower frequencies become more
over-sampled, so no information is lost. Seems too simple, but I can't
mathematically show it won't work, since the oversampling makes some sense.

My argument is that this won't work, and it would require a nasty SSB
phasing network on one of two input channels (analog equivalent of Hilbert
transform) to provide a constant 90 degree shift over the entire band (since
sample clocks can't be quadrature), with equivalent delay on the other. 
Then a Hilbert transform at baseband in GR before they are summed into a 200
MHz complex baseband.

In either case the anti-aliasing filters would need cutoff increased.

Lou
 





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