Forcing TX power on the MM8108-EKH05

Software Embedded
1

Hello,

I’m currently developping a system using the MM8108-EKH05 on the TX side and the MM8108-EKH19 on the RX side.
I’m having a hard time setting the transmission power to the maximum available (26dbm).

I am currently stuck at exactly 14 dBm (25 mW).

Here is my configuration:

  • Country Code: Set to "US" in config.hjson.

  • BCF: Set to bcf_mf15457.mbin and successfully flashed via OpenOCD/Python script.

  • Channel: 28 / 916 MHz.

  • Power Supply: USB-C 5V 3A.

  • Measurement: Mini-Circuit Power Sensor (50 - 6000 MHz).

I’v tried using mmwlan_override_max_tx_power(26); too but i’m getting the same result.

here is my void app_init(void) for more context

void app_init(void)
{
    printf("\n\n--- RPI -> STM32 -> HALOW ---\n\n");

    SPI_Slave_Init();

    HAL_SPI_Receive_IT(&hspi1, spi_rx_buffer, SPI_PAYLOAD_SIZE);

    // low QoS config
    struct mmwlan_qos_queue_params fpv_qos = {
        .aci = 3,         // ACI 3 = Voice (TOS 0xC0 - LwIP)
        .aifs = 2,        // inter-trame waiting time
        .cw_min = 1,      
        .cw_max = 1,  
        .txop_max_us = 0 
    };

    mmwlan_set_default_qos_queue_params(&fpv_qos, 1);
    mmwlan_set_power_save_mode(MMWLAN_PS_DISABLED);

    app_wlan_init();

    mmwlan_override_max_tx_power(26);

    mmipal_set_link_status_callback(link_status_callback);

    printf("connection to the OpenWrt AP...\n");

    app_wlan_start();

    mmwlan_ate_override_rate_control(MMWLAN_MCS_1, MMWLAN_BW_8MHZ, MMWLAN_GI_NONE);
    printf("8 MHz / MCS 1 setted.\n");


    while (!is_network_ready) {
        mmosal_task_sleep(10);
    }

    struct udp_pcb *pcb = init_udp_pcb();
    if (pcb != NULL) {
    	pcb->tos = 0xC0;
        udp_broadcast_tx_start(pcb);
    }

    (void)get_mode;
    (void)udp_broadcast_rx_start;
}

Thank you for your help,
Nathan.T

2

Hi Nathan,

mmwlan_override_max_tx_power will only limit the TX power, it will never increase it past the default value in the regulatory database:

The US Max Tx EIRP (dBm) for all channels is 36, so setting 26 will actually be reducing the TX power. Can you try removing the override and measuring the power?

As an aside, mmwlan_override_max_tx_power should be called between app_wlan_init and app_wlan_start, rather than after app_wlan_start (see note in docs above)

Cheers

3

Thanks for the response.

The function is indeed called between init and start in my code :). However, even with the override removed completely, the TX power remains physically capped at 14 dBm on the power meter.

Is it possible that, since I purchased the eval kit in the EU, the maximum power is hardcoded/locked in the hardware for regulatory reasons, even though I configured the country code to US? Or should I be using a different BCF file than bcf_mf15457.mbin?

Thanks again for your help.

4

Weird, I must have gotten my wired crossed when reading the code :sweat_smile:

Assuming you updated the country code in the mmconfig (which should be the case if you are associating to a US based AP) there shouldn’t be any EU restrictions as far as I know.

Can you confirm how/where you are measuring the power? That should help with diagnosing on our side

5

Thanks for the clarification!
​Regarding the measurement, I performed a conducted measurement: I connected the EKH05 directly via its SMA connector to a PWR-6LGHS USB Power Sensor (50 MHz - 6 GHz, -45 to +10 dBm) using a 20 dB attenuator to not fry the equipment. The reading consistently sits at exactly 14 dBm.
​To confirm this wasn’t a measurement artifact, I also did some Line-of-Sight (LOS) tests outdoors (in a mostly openfield terrain). I completely lost the connection at ~250m, which seems logical with 14 dBm.
​To address the mmconfig: yes, I did set “wlan.country_code”: “US” in my config.hjson and flashed it to the Config Store using the program-configstore.py tool.

​Is there any other parameter that could clamp the PA hardware internally?