Low output power on DevBoards

[Rashid Talib]

Hi

I measured the CW output power of several DevBoards (nRF52832 and nRF52840) and the output power is much lower than expected.

Setup:

• nRF52832 or nRF52840 DevBoard connected to spectrum analyzer using Murata RF Probe (see image below)
• Nordic DTM firmware running in Tx mode, output power = 0dBm, pattern = "vendor specific", packet length: 1 byte, channel: 19
• Measured power on spectrum analyzer is as low as -3dBm (cable loss already calibrated out)

Question:

Why is the measured power so low? I would have expected something in the range of 0..-1dBm. The spectrum analyzer was recently calibrated and I verified the measurement with 4 different boards with equal results. If I set the output power of the chips to +4dBm, the measured power increases by 4dB as expected.

For me there are three options:

1. The chips are not working properly
2. The ANT pin is not properly matched to 50 ohms
3. The Murata socket / probe combination lead to high loss

Thanks for your help & best regards

Rashid

[haakonsh]

You need to set up the radio to transmit an unmodulated constant carrier. A modulated radio packet will not have 100% duty-cycle and the measured output power will show as lower than expected. 

For me there are three options:

1. The chips are not working properly
2. The ANT pin is not properly matched to 50 ohms
3. The Murata socket / probe combination lead to high loss

1. It's not very likely that all of the devices are not working. 
   
   
2. The DK's are properly impedance matched to 50 ohm.
   
   
3. There is some loss in cabling and connectors, but it's usually closer to 0.5dB. Murata is a good manufacturer, I'd trust them to make a good cable.

[Rashid Talib]

Hi Haakonsh

Thanks for your reply.

I'm already seting up the radio to transmit an unmodulated carrier (using the DTM settings mentioned before). I'm quiet sure that both my setup und the firmware is working properly. If you could provide a standalone firmware that generates a CW at channel 19 with 0dBm output power, I will repeat the measurement and let you know the result.

Best regards

Rashid

[haakonsh]

Hey Rashid, 

You can run the Radio Test Example, with arguments 'start_channel 19' followed by 'start_tx_carrier'.

BR,
Håkon.