nRF9160 detecting antenna to prevent high power draw

RE: nRF9160 detecting antenna to prevent high power draw

Michal — Fri, 19 Jul 2024 16:32:27 GMT

[quote user="Vincent44"]So, rather than an antenna issue, I tend to think that the modem is capable to detect poor network reception, and adjust its output power, which would explain the higher power consumption without the antenna. Is this behavior possible ?[/quote]

Yes. I have heard that even without antenna nRF9160 is able to connect to the network. It makes sense that the network is asking for a higher power output from the device, since it is much less efficient than with an antenna.

For a proper antenna disconected/lost connection testing you may need to use some kind of faraday cage (a metal box or similar).

Best regards,

Michal

RE: nRF9160 detecting antenna to prevent high power draw

Vincent44 — Fri, 19 Jul 2024 08:49:11 GMT

I made new tests, and my issue might not be directly related to the missing antenna, but rather to bad network coverage.

- I tested again in the same conditions (same board, same place), and I got the following results

We can see that the power is rather normal during the search, and the high spikes only occur when the device seems to actually pickup something (not sure how exactly the cellular connection process works).

In my previous post, the device could find the network almost instantly (even without antenna), which resulted in different interpretation of the measurement.

So, rather than an antenna issue, I tend to think that the modem is capable to detect poor network reception, and adjust its output power, which would explain the higher power consumption without the antenna. Is this behavior possible ?

RE: nRF9160 detecting antenna to prevent high power draw

Vincent44 — Tue, 16 Jul 2024 13:45:21 GMT

Hi Øyvind,

Thanks for your quick response.

The schematic is very similar to what is suggested.

The code looks like this. I remove all the error checking to make it more readable.

- Init() is called once at startup

- Enable() is called whenever I need to restart/reconfigure the modem (for example, if the GPS was used)

void CELLULAR_MODEM_Init(void)
{
	nrf_modem_lib_init();	
	
	// Indicate that the AUX pin is used/redirected for GPS
	nrf_modem_at_printf("AT%%XANTCFG=1") ;
		
	// Setup COEX0 to be set to 1 when the frequency used by the modem is in GNSS range.
	// Depending on the hardware, this is used to for either :
	// - Enable the GPS frontend (LNA)
	// - Enable power supply for an external active GPS antenna	
	err = nrf_modem_at_printf("AT%%XCOEX0=1,1,1550,1615") ; 	// Using the entire LNA operating frequency range

	lte_lc_init() ;
}


void CELLULAR_MODEM_Enable(void)
{
	// Make sure modem is stopped
	nrf_modem_at_printf("AT+CFUN=0") ;

	// Setup mode: enable LTE-M and NB-IOT. Disable GNSS.
	nrf_modem_at_printf("AT%%XSYSTEMMODE=1,1,0,0") ;	// No preference: Auto
		
	// Start modem 		
	nrf_modem_at_printf("AT+CFUN=1") ;

	// Enable PSM
	lte_lc_psm_req(enablePSM);

	// Connect to netwrok
	 lte_lc_connect_async(lte_handler);
}

RE: nRF9160 detecting antenna to prevent high power draw

Øyvind — Tue, 16 Jul 2024 13:04:46 GMT

Hello,

I will need to discuss the issue internally with our antenna experts. Are you able to provide more information on your setup i.e. schematics and layout, or have you had a design review of your custom board?

Our development kit uses the modem antenna library which writes the MAGPIO and COEX0 configuration to the modem after the Modem library has been initialized. The configuration depends on the selected board and the used GNSS antenna type, onboard or external.

This is done at startup of the board. E.g. the Thingy:91 has a combined antenna for LTE and GNSS, and uses the following setup to configure the MAGPIO through the QM12038 RF switches:

Kind regards,

Øyvind