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6

That's an expected phenomenon: Real-world physical systems tend to be frequency-selective (i.e. not constant over frequency), and "at large scale" low-pass systems. This applies to amplifiers, mixers, oscillators, and even transmission lines and connectors. So that's normal. Ettus even publishes exactly such measurements at https://files.ettus.com/...


4

For a complex-valued sampled stream, the sample rate must be greater than twice the signal represented. The sample rate in your graph is set to 384k, so it's not possible to represent a 98400 kHz signal. GNU Radio won't stop you, though. Mathematically, when you try to generate a sampled signal that's too high, you get aliasing. As an experiment, try ...


2

You've got a few very concerning conceptual and technical problems there, many of which will be adressed by the console output, which you should probably read! You can only sweep within your nyquist bandwidth. That is at most 25 MS/s (at 16 bit sample depth) or 50 MS/s (at 8 bit sample depth) for the N210 You want a single-tone sweep from negative baseband ...


1

500 kHz = 0.5 MHz = 0.0005 GHz. You're providing a signal at +500 kHz, and then upconverting it to produce a signal at 2.5005 GHz. Are you sure that your measurement of the output frequency (and the USRP's oscillator) is precise enough to distinguish between 2.5000 GHz and 2.5005 GHz, absolute? A way to tell if your signal generation is having any effect is ...


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