The e4k does the filtering but has an analog output.
The RTL2832 is in
effect an USB ADC.
apologies if this is obvious to everyone and has already been posted (I have not checked
the whole history of this ml), but indeed by connecting a couple of wires to the I or Q
differential
inputs of the RTL2832 you do get a fine 2 MS/s oscilloscope. This unfortunate AGC means
that
DC signals cannot be monitored (even after soldering the wires after the common mode
cutoff capacitors),
but neverless this does provide a 40 fold sampling rate improvement with respect to the
use of sound
cards as A/D converters (
http://sequanux.org/jmfriedt/199999720input_middle.png and
http://sequanux.org/jmfriedt/199999720input_top.png for the I and Q measurements when an
input signal of
199.999720 kHz is generated by a synthesizer in order to synchronize with the sampled
data, ie the
sampling clock is off by 1.4 ppm, not too bad !).
JM
--
JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 32 av. observatoire, 25044 Besancon,
France