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[Discuss-gnuradio] USRP2 / RFX2400 choppy transmit

From: Michael Johnson
Subject: [Discuss-gnuradio] USRP2 / RFX2400 choppy transmit
Date: Mon, 20 Dec 2010 11:12:40 -0600


I'm seeing what I think is choppy transmission from a USRP2 with and RFX2400 daughtercard.

I have two USRP2s - one acting as the transmitter and one as the receiver. When I transmit a continuous tone, the received samples all look fine, no discontinuities. However, if I transmit canned packets, sometimes ( about 1 in 30 ) they come out on the receiving end very choppy - meaning the power drops to zero at various points in the packet for various lengths of time. It also appears that the amount of time spent at zero power increases the transmission time of the packet. (i.e. classic underflow?)

I'm using the tx_samples app in ./gnuradio/usrp2/host/apps to transmit canned packets and I've used both rx_streaming_samples and  usrp2_rx_cfile.py to receive the data:

./gnuradio/usrp2/host/apps/tx_samples -e eth0 -m 36:ab -f 2600000000 -g 21 -i 8 -I ../code/C/tx/tx_samps.dat

./usrp2_rx_cfile.py -m "35:7c" -f 2600000000 -d 20 -g 21 rx_samps.dat

./rx_streaming_samples -m "35:7c" -f 2600000000 -d 20 -o rx_samps.dat

I thought maybe it was a PA settling issue, but I've padded to front of the packets with tons of zeros with no luck.

Anyone know what's going on?


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