How to achieve a measured conductive Tx Power of +21 dBm using any NCS sample app?

RE: How to achieve a measured conductive Tx Power of +21 dBm using any NCS sample app?

Vidar Berg — Mon, 13 Mar 2023 12:54:55 GMT

Hi,

[quote user="Starbuck"]Wouldn't you expect the skyworks,sky66112-11 driver to initialize the CHL & CPS pins?[/quote]

Yes, I assumed the same at first. However, as implied in the documentation here and shown by the implementation here, the generic FEM GPIO driver is only controlling the CTX and CRX signals. The other signals have to be set by the application as you found out. This should have been documented more clearly.

The application may still use the properties exposed by your fem node. The Bluetooth direct test mode sample demonstrates how here: https://github.com/nrfconnect/sdk-nrf/blob/main/samples/bluetooth/direct_test_mode/src/fem/generic_fem.c#L52

[quote user="Starbuck"]Regarding my RF Power Meter, it is really nice and portable (affordable too). I travel a lot and I'm getting into flying FPV drones as a hobby of mine so I'm always looking for compact portable test equipment. I highly recommend it![/quote]

Thank you for providing the link! I am considering this for my home lab.

RE: How to achieve a measured conductive Tx Power of +21 dBm using any NCS sample app?

Starbuck — Fri, 10 Mar 2023 17:47:27 GMT

Regarding my RF Power Meter, it is really nice and portable (affordable too). I travel a lot and I'm getting into flying FPV drones as a hobby of mine so I'm always looking for compact portable test equipment. I highly recommend it!

Here's a link to it: https://www.immersionrc.com/fpv-products/rfpwrv2/

RE: How to achieve a measured conductive Tx Power of +21 dBm using any NCS sample app?

Starbuck — Fri, 10 Mar 2023 17:30:19 GMT

Hi Vidar,
I agree that is part of the problem. I found that too this morning. However, correcting that in my overlay file didn't bring the FEM out of bypass mode. But after initializing the CHL & CPS pins correctly in main.c I was able to measure +21 dBm. The code snippets below fix the issue, but I'm still not understanding why I need to initialize CHL & CPS in main.c. Wouldn't you expect the skyworks,sky66112-11 driver to initialize the CHL & CPS pins?

Changing the nrf52840dk_nrf52840.overlay file to this did NOT fix the issue:

/ {
	nrf_radio_fem: fan_evbt840x_fem {
		compatible = "skyworks,sky66112-11", "generic-fem-two-ctrl-pins";
		ctx-gpios = <&gpio0 17 GPIO_ACTIVE_HIGH>;
		crx-gpios = <&gpio0 19 GPIO_ACTIVE_HIGH>;
		cps-gpios = <&gpio0 6 GPIO_ACTIVE_LOW>;
		chl-gpios = <&gpio0 8 GPIO_ACTIVE_HIGH>;
		tx-gain-db = < 18 >; // See CONFIG_BT_CTLR_TX_PWR_ANTENNA comment before changing this value
	};
};

Setting the cps-gpios pin to GPIO_ACTIVE_HIGH didn't work either.

The code snippets below allowed me to measure +21 dBm:

	printk("Bluetooth initialized\n");

	nrf_gpio_cfg_output(APP_CHL_PIN);
    nrf_gpio_cfg_output(APP_CPS_PIN);
	nrf_gpio_pin_set(APP_CHL_PIN);
	nrf_gpio_pin_clear(APP_CPS_PIN);

/ {
	nrf_radio_fem: fan_evbt840x_fem {
		compatible = "skyworks,sky66112-11", "generic-fem-two-ctrl-pins";
		ctx-gpios = <&gpio0 17 GPIO_ACTIVE_HIGH>;
		crx-gpios = <&gpio0 19 GPIO_ACTIVE_HIGH>;
		tx-gain-db = < 18 >;
	};
};

Thank you for helping me understand this. I'm still on the Zephyr learning curve. It is very appreciated!

RE: How to achieve a measured conductive Tx Power of +21 dBm using any NCS sample app?

Vidar Berg — Fri, 10 Mar 2023 14:35:14 GMT

Hello,

Sorry for the delay. I compared the pinout in your overlay with the pinout Fanstel suggest in the "Control Skyworks Power Amplifier" section of their product specification (https://static1.squarespace.com/static/561459a2e4b0b39f5cefa12e/t/63de927a519c1b69364b15f2/1675530877718/BT840F-p+Product+Specifications.pdf) and it looks like you may have gotten the CSD and CPS pins wrong? CPS controls the bypass mode and if I am reading things correctly, you have CSD set to '1' and connected to the input CPS input on the FEM.

By the way, it looks like you have a neat tool there for measuring TX output power. I have not seen anything like it before.

Best regards,

Vidar