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From: | lists |
Subject: | Re: Signal Capture and Playback Noise |
Date: | Thu, 27 Jan 2022 15:01:22 -0800 |
I think you would need your SDR and signal generator phase locked to get a perfect frequency measurement. Windowed measurements aren't perfect. Your signal generator probably has a 10MHz reference input and perhaps output on the back. I don't know about the SDR.
Hi GNU Radio users,
I am experiencing some interesting noise captured on a signal analyzer when trying to playback a captured signal using an Ettus B200 with both GNU Radio blocks and UHD example code. The UHD example code I am using is:
The GNU Radio blocks I am using are simply a USRP Source into File Sink for capture and a File Source into USRP Sink for playback (both programs operating at a 10M sample rate).
The signal I am capturing is a 500MHz pure sine wave fed directly out of a signal generator into the TX/RX port of the B200. The playback with noise I am receiving is directly out of the B200 TX/RX port into a signal analyzer and is pictured here:
Is this peak 1kHz from the carrier expected? Could this be the LO or some other noise on the board leaking through due to a lack of filtering? Is this re-creatable on other hardware? I can send the captured data if there isn’t an obvious answer to why there is a signal at 499.999MHz.
Another piece to the puzzle I feel like I should mention is that when running “tx_waveforms –rate 10000000 –freq 500000000” and feed it directly into signal analyzer the output is only a peak at 499.999MHz…
Is this offset within tolerance of B200 hardware, or is there a bigger issue happening here?
Thanks in advance for any help, Nick Restivo
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