On 22/03/2023 18:42, jmalo...@umass.edu wrote:
Nothing interesting, I am currently just “toying around” to understand
the device(and sdrs) better, and the lowest the closest available
signal generator I have goes to 100 khz. I was using 3 Mhz before but
I figured if the API was telling me that it was able to be tuned lower
than why not try reducing the input frequency.
I am currently just interested in trying to interpret the data that
comes from the ADC. I saw on the daughterboard there is a lot more
going on than just two mixed signals, so I am asking if there any
particular formula or considerations I should be making when trying to
recover the original signal. Ideally(for my application), I would be
able to directly sample voltages on the antenna, but since that is not
possible I need to work around this instead.
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What you get in I/Q signals is a *linear proxy* for the instantaneous
voltages appearing on the antenna terminals. If you really
want just a high-speed ADC, there are other products out there that
are closer to what you need. Trying to cajole a *radio*
into being a laboratory high-speed ADC, without regard to its
"RFness" is asking for heartburn.
Signals are typically filtered and amplified and mixed-down to
baseband, filtered and amplified again, and then presented to
a *complex* ADC. After that, the signals are usually digitally
filtered and down-sampled to produce an alias-free complex-baseband
to the application at the requested sample rate.
https://getmyuni.azureedge.net/assets/main/study-material/notes/electronics-communication_engineering_analog-communication_complex-baseband-representation-of-bandpass-signals_notes.pdf
But if you're looking to *measure* actual voltages as seen at the
antenna input, you cannot do that directly with a typical
radio (whether analog or DSP). But what you *can* do is engage in a
*calibration* process using sources of known
power--this works because the transformations described above are all
more-or-less linear.
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