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[Discuss-gnuradio] Tx and Rx delay within USRP motherboard and daughterb


From: hanwen
Subject: [Discuss-gnuradio] Tx and Rx delay within USRP motherboard and daughterboard
Date: Fri, 15 Dec 2017 23:53:55 +0100

Hi,

I did a test to figure out how much delay is within the hardware (FPGA DUC/DDC, ADC/DAC, mixer, filters and amplifiers, etc.)

In the test using UHD at host side, signal transmission is scheduled at t0 and received at t0 + T. The receiving synchronization is based on cross-correlation which should be quite precise with error below one sample.

I set my X310 + SBX at sampling rate of 15.36MS/s and 30.72MS/s and measured the delay T as about 3.1us and 1.6us respectively. It seems to be scaling linearly down versus sampling rate.

The loop-back test can only measure the total TX+RX delay. However, it'd be more interesting to know:
- what are the TX and RX delays specifically
- what is the major part of in the delay (filters in the FPGA?)

Thanks.

Br, Hanwen

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