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   ____ ______      / __/___  ____     \   \
  / __ `/ ___/_____/ /_/ __ \/ __ \  \  |   |
 / /_/ / /  /_____/ __/ /_/ / /_/ /  /  |   |
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This is a collection of custom blocks that are not directly associated with a project. For sample applications see:


Like GNU Radio, this module uses maint branches for development. These branches are supposed to be used with the corresponding GNU Radio branches. This means: the maint-3.7 branch is compatible with GNU Radio 3.7, maint-3.8 is compatible with GNU Radio 3.8, etc.

Wireshark Connector

This blocks outputs PDUs in the PCAP format which is supported by all common network monitoring applications. Some examples are Wireshark, Tshark, and tcpdump. Currently, it supports WiFi packets with Radiotap header and ZigBee.

For further information about Radiotap, PCAP, and Wireshark see:

Packet Pad

Adds a configurable number of zeros before and after a burst. The burst has to be started with an tx_sob, and ended with a tx_eob tag. From time to time I had issues when I did not pad the sample stream. This block helps to investigate that. It is also handy for loopback testing when there is no continues sample stream. Furthermore, this block can add a tx_time tag to every burst that lies a configurable number of seconds in the future. This is handy to buffer the sample stream for a short time to avoid underruns during the transmission, which lead to corrupted signals. You have to set the sync option to 'PC source' for this feature.

Burst Tagger

Tags a burst / packet / bunch of samples with tx_sob and tx_eob tags. This is useful if the SDR is operating in half-duplex mode. With adding a tx_eob the USRP switches back to receive mode immediately. That way, direct responses like ACKs are not missed.

The block searches for a special tag that indicates the start of a burst. The name of this tag is configurable. The tag should indicate the length of the packet in samples. Also a multiplier can be specified, which multiples the length given in the tag.

Packet Dropper

Drops a configurable percentage of messages. I used it to test protocol logic like ACKs, retransmission and stuff.

Periodic Msg Source

This block sends messages at regular intervals much like the Message Strobe block in mainline GNU Radio. With this block you can also configure the number of packets that are sent. When all normal messages are sent, the blocks sends a final PMT_EOF message to indicate that it is done. I used this block for automated performance tests with no-GUI flow graphs.

Pad Tagged Stream

Pads an incoming tagged stream with 0s to the set buffer size. Padding is applied to the tail of the tagged stream.

This is useful when transmitting packetized data by using a Pluto as SDR. The Pluto does currently not support a partial buffer flush triggered by an incoming tagged stream. Therefore this block pads incoming tagged stream to fill the Pluto buffer to enforce an immediate transmission.


git clone
cd gr-foo
mkdir build
cd build
cmake ..
sudo make install
sudo ldconfig