NoMac Mode

NoMac mode bypasses the Symphony Link MAC protocol and gives users the ability to evaluate the performance of the LoRa modulation format and the Semtech LoRa radio used by the LL-RLP-20 and LL-RXR-27. After shifting to NoMac mode from Symphony Link mode, the NO_MAC Prelude form opens.

Radio parameters

Set the desired radio parameters by checking the appropriate radio button from Prelude's Mode panel. The radio parameters of each selection are defined below.

Radio parameters

Transmit power

In NoMac mode, the transmit power is always set to the highest power available from the module.

Time on Air

The LoRa physical layer allows many combinations of low-level parameters like the spreading factor (SF), bandwidth and coding rate (CR). These parameters affect the data rate, sensitivity, and time on air. In NoMac mode, Prelude limits selection or radio parameters to the three options listed in the table below. Each selection represents a trade-off between data rate and link margin.

Radio parameter set


Bandwidth (kHz)


low rate / max distance




mid rate / mid distance




max rate / short distance






Prelude allows several operating frequency bands: 868.5 - 868.6 MHz; 868.7 - 869.2 MHz; 869.4 - 869.65 MHz; 869.7 - 870 MHz; and 902 - 928 MHz. The entire LoRa transmission must fit within any one of the listed frequency bands.

Clicking the Set Frequency button sets the center frequency of the LoRa transmission.  If the selected radio parameters are incompatible with the selected frequency, Prelude will issue a warning similar to the following:



To open the Transmit Window, click the Show Transmit button.


The Transmit Window appears. To transmit a message, enter the text payload in the Message edit box and click the Transmit button.

The evaluation board's module will transmit the message using the selected radio parameters. After the transmission is complete, the module sets the IRQ_FLAGS_TX_DONE flag. Prelude automatically clears all IRQ flags each time the Transmit button is clicked so that new IRQ events may be observed.


Prelude will repeatedly transmit the same message if the Repeat check box is selected. Prelude will send the message, wait one second, and then attempt to transmit again. If the module is still transmitting the previous message, Prelude will wait another second and then attempt to transmit again. This process repeats until either the Stop button is clicked or the Repeat check box is de-selected.



Click the Start Receiving button to begin receiving messages sent from other NoMac-mode modules. Prelude will write the selected radio parameters to the module before it sets the module to receive. Upon receipt of a message, the module sets the IRQ_FLAGS_RX_DONE flag. Prelude then retrieves the message from the module and displays the message in the Receive Window.

The module is able to receive any LoRa transmissions with matching radio parameters.


Echo mode

A module using NoMac provides a special operating mode called Echo mode. In Echo mode assigns a module to be either a master or slave node. The master node initiates an echo transaction by transmitting a LoRa message. The slave node receives the transmission from the master and then promptly echos by transmitting the same message. The master node then attempts to receive the echo from the slave node.

To use Echo mode, attach an evaluation board to Prelude and select Options > Set Remote Echo Mode. This configures the attached module to be a slave node.

Echo mode

After the slave node is configured, detach it from Prelude and then attach the intended master node. Ensure the master node is using the same radio parameters as the slave node and then open the Transmit window and select the Echo Master check box.

Enter the desired message in the Message edit box and click Transmit.

Select the RF path

Setting the RF path is done in the same way for NoMac and Symphony Link modes.

Switching to Symphony Link mode

To switch Prelude to control the module using Symphony Link mode, select Options > Symphony Link. The NO_MAC Prelude form will close and a new Symphony Prelude form will open.


While in NoMac mode, Prelude's logging functionality is identical to that in Symphony Link mode.


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