nRF52840 + FEM nRF21540 Continuous Wave Test (Radio_test)

[VishnuPrasad V]

Hi Team,

We are on the Pre-Production stage of our Product, which uses the nRF52840 (forBLE)  with the FEM nrf21540(new)

We are aiming to get power out of 20dBm.

To get the Radio Characteristics we are testing it on the Spectrum Analyzer. Our Interest is in the Continuous-wave test.

We are using the  radio_test example from the latest nrfConnect SDK 1.7.0  for nRF21540_nRF52840 dk. 

We have remapped the development kit pins to use with our custom board.

****************************************What we need Help from nRF*******************************************************

1) What is the Sequence of commands I should use,  to get the continuous transmission wave on the Spectrum analyzer?

2) To validate the nrf21540 functioning I like to adjust the gain parameters on 21540, What sequence should I use for that?

3) Will the nrf21540 commands to change the gain over SPI works ? (we are not able to observe the change in the 

4) With the same Radio Test example can I use the Mode pin to control the Gain setting (10/20 dB setting )?

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Background Data

We did some test with the Radio_test example, The commands I used for continuous tx testing was as follows: (not sure these are the correct way)

> nrf21540 antenna  ant_1             (we are using  antenna 1)

> start_cahnel 2

> start_tx_modulated_carrier

with Spectrum analyzer set to 10.KHz Resolution Bandwidth we were getting  -8dBm , when I changed to 100kHz RBW I was able to observe  2dBm etc.

with 52840 gain set to 8dBm  We were able to get 3 dBm at 10 kHz RBW, with the same radio settings changing  RBW to 100kHz I was getting around 12 dBm.

Are these behaviors expected? or are we doing something wrong?

 Thanks!

VishnuPrasad V

[Bendik Heiskel]

Hi,

1) What is the Sequence of commands I should use,  to get the continuous transmission wave on the Spectrum analyzer?

To start a carrier of 8dBm on channel 40 the sequence is:

start_channel 40

output_power pos8dBm

start_tx_carrier

When the nrf21540 is connected this will use the default antenna and TX gain which is ant_1 and 20dBm. If no start channel or output power is set before starting the TX carrier the defaults will be used which are channel 2 and pos0dBm.

2) To validate the nrf21540 functioning I like to adjust the gain parameters on 21540, What sequence should I use for that?

To change the TX gain the following command must be used before staring the tx carrier:

nrf21540 tx_gain x

3) Will the nrf21540 commands to change the gain over SPI works ? (we are not able to observe the change in the 

The command above uses the SPI interface of the nRF21540 to change the TX_gain. If you are not able to observe changes to in the selected TX gain, the SPI pins may be configured wrong in the devicetree .

4) With the same Radio Test example can I use the Mode pin to control the Gain setting (10/20 dB setting )?

No there is no control over the Mode pin when using the radio test example. To change between 10dBm and 20dBm the SPI interface must be used.

with Spectrum analyzer set to 10.KHz Resolution Bandwidth we were getting  -8dBm , when I changed to 100kHz RBW I was able to observe  2dBm etc.

with 52840 gain set to 8dBm  We were able to get 3 dBm at 10 kHz RBW, with the same radio settings changing  RBW to 100kHz I was getting around 12 dBm.

Are these behaviors expected? or are we doing something wrong?

When measuring the output power a resolution bandwidth of at least 100kHz must be used. If the RBW is too low the measurement will not be correct. You will also measure lower output power if the matching networks for the nRF52840 and the nRF21540 are not tuned.

 

Best regards,

Bendik