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Why a bench test shows no DJI detections

The most common reason is not the unit. DJI aircraft broadcast DroneID only while the motors are spinning.

The one thing to check first

Important Powering on a DJI aircraft does not start the DroneID broadcast. The motors must be spinning. An aircraft sitting on the bench with its lights on will not appear, no matter how close it is to the unit.

Remote ID broadcasts from other aircraft behave differently and may appear while the aircraft is stationary, which is why a bench test can show Wi-Fi or Bluetooth detections and no DJI detections at the same time.

If the motors are spinning and there is still nothing

Work through these in order.

  1. Confirm the antenna etched DRAGON SDR is on the port marked Dragon SDR, hand-tight by the connector nut. This is the primary DJI receive port. A loose or swapped antenna is the most common hardware cause.
  2. Confirm all three detection services are running:
sudo systemctl status zmq-decoder dji-receiver dragonsync
  1. Confirm the detection hardware is enumerated:
lsusb
  1. Watch the DJI receiver log while the aircraft’s motors are running:
journalctl -u dji-receiver -f
  1. Confirm the detection stream itself is producing data. This listens for ten seconds and prints the first message it receives:
timeout 10 python3 -c "
import zmq
c = zmq.Context()
s = c.socket(zmq.SUB)
s.connect('tcp://127.0.0.1:4221')
s.setsockopt_string(zmq.SUBSCRIBE, '')
s.setsockopt(zmq.RCVTIMEO, 5000)
try:
    print('DJI DroneID:', s.recv_string()[:100])
except:
    print('DJI DroneID: No data')
"

If the services are active, the hardware is listed, and the stream still reports no data with motors running in range, restart the detection services and try again:

sudo systemctl restart zmq-decoder dji-receiver

Critical If at any point you have changed Wired connection 1 or the addresses 172.31.100.1 and 172.31.100.2, that is the cause. That connection is the internal link to the detection SDR and must stay as shipped.

Still nothing

Open a support request and include the output of the service status command and a diagnostic bundle. See Opening a support request and building a diagnostic bundle.

Related

  • WarDragon User Guide, Section 6 — verifying detection services
  • WarDragon User Guide, Section 10.4 — no detections

WarDragon is manufactured by Millenium Products Inc. Technical support for purchased kits is requested through the support page. Purchasing and quote requests go through the contact form.