stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?

friedtj friedtj at free.fr
Sat Jul 7 10:21:01 UTC 2012


> 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




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