Dear GNU Radio Community, I hope you're doing well. I am currently working on a project where I’m trying to transmit a text file from one USRP device to another using GNU Radio Companion.
System Setup: Hardware: - 2x USRP N210 devices - Basic TX/RX daughterboards - Separate TX and RX antennas - Clock/Time source: Mimo cable Transmission Flowgraph: - File Source (repeat = yes / no, tried both) - Head block - Stream to Tagged Stream (packet_len) - Repack Bits (8 to 1) - GMSK Mod - USRP Sink Receiver Flowgraph: - USRP Source - GMSK Demod - Repack Bits (1 to 8) - File Sink USRP Configuration: - Center Frequency: 145 MHz (within board range) - Sample Rate: 500k - Gain: 28 dB Problem Description When I run the transmitter flowgraph, I can see the signal in the frequency display, but the receiver does not seem to capture any data. In addition, I’m getting the following recurring error in the console: "usrp_sink: error: tag gap (nitems_read = 1024) no more items to send in current burst, but got 3072 more items, dropping them." After this, the simulation hangs and I am unable to stop the flowgraph normally — I have to force quit GNU Radio Companion. When I disable "repeat" in the File Source, the signal disappears altogether, and nothing I can see on the transmission side graph. My Questions: 1. Could you help me understand the root cause of the “tag gap” error and what’s actually happening? 2. Is my approach to the flowgraph design correct for this kind of simple file-based digital communication? 3. Could this be an issue related to packet formatting or tagged stream mismatch? 4. Are there known limitations when using Basic TX/RX boards with GMSK in GNU Radio for such tasks? I have attached my `.grc` files for both the TX and RX sides for reference (or will share them via link if attachments aren’t allowed). I understand that debugging full flowgraphs may be beyond the scope here, but I would appreciate any pointers on what I might be doing wrong or how I could better debug this issue. Thank you in advance for your time and support! Best Regards, Namira Tahsin
USSRP_2.grc
Description: USSRP_2.grc
USSRP_1.grc
Description: USSRP_1.grc
