Having very short range with custom board

[Tai]

Hello everyone,

I got an issue with the custom board nRF52832 (Raytac BLE module) as I only achieve very short distance between the BLE device and Android app without data loss. This distance is about 50 cm. The RSSI I noticed is below -70dBm.

With same code, it perfectly ran on nRF52 DK and the range I tested without data loss is about 5 meters. 

I tried to increase TX power as the following code ( using sd_ble_gap_tx_power_set()). However, it didn't improve much. Is there any suggestion in this case?

static void advertising_init(void)
{
    uint32_t               err_code;
    ble_advdata_t          advdata;
    ble_advdata_t          scanrsp;
    ble_adv_modes_config_t options;
		int8_t tx_power_level = 4;

    // Build advertising data struct to pass into @ref ble_advertising_init.
    memset(&advdata, 0, sizeof(advdata));
    advdata.name_type          = BLE_ADVDATA_FULL_NAME;
    advdata.include_appearance = false;
    advdata.flags              = BLE_GAP_ADV_FLAGS_LE_ONLY_LIMITED_DISC_MODE;
		advdata.p_tx_power_level   = &tx_power_level;
			
		sd_ble_gap_tx_power_set(tx_power_level);
	
    memset(&scanrsp, 0, sizeof(scanrsp));
    scanrsp.uuids_complete.uuid_cnt = sizeof(m_adv_uuids) / sizeof(m_adv_uuids[0]);
    scanrsp.uuids_complete.p_uuids  = m_adv_uuids;

    memset(&options, 0, sizeof(options));
    options.ble_adv_fast_enabled  = true;
    options.ble_adv_fast_interval = APP_ADV_INTERVAL;
    options.ble_adv_fast_timeout  = APP_ADV_TIMEOUT_IN_SECONDS;

    err_code = ble_advertising_init(&advdata, &scanrsp, &options, on_adv_evt, NULL);
    APP_ERROR_CHECK(err_code);

    ble_advertising_conn_cfg_tag_set(CONN_CFG_TAG);
}

Thanks!

[RK]

share your design. First thing comes to me is bad placement of the Raytac module affecting the antenna

[Tai]

Thanks for your prompt reply. The following are schematic and PCB. I followed schematic from manufacture as described in page 33 (here). 

[RK]

You have the module in the middle of the board, in almost every case I've EVER seen you want it with the antenna at the edge. It's impossible to tell from the attachments if you have a ground keepout area beneath and as far to either side of the antenna as possible again as recommended in the documentation (sections 2.3 and 2.4). That doesn't actually say anywhere it should be at board edge but the pictures rather show that. You have components right next to the antenna and I'm guessing you have none, or nowhere near enough ground keepout on the top and/or bottom layer. Without following that, the antenna isn't going to work basically at all. 

[Tai]

Yeah, you're right. I didn't follow the RF layout suggestion. Thanks for your answer! I'll be more careful in the next design.

[Tai]

Btw, could you suggest to me the placement of other components compared with BLE module so that I can have the highest efficiency. Please correct me if I am wrong:

1) The antenna should be placed at the edge.

2) All components shouldn't be next to antenna.

3) Strictly follow layout reference for ground keepout area.

Thanks,

Tai