Keeping RADIO on TX_ENABLED for NRF5X

[sheekshook]

Hi all, 

I would like to check and see if its viable to keep radio on TX_ENABLE throughout the radio's operation, ie keeping TXEN = 1; at all times or keeping radio only on TX_IDLE between transmissions. 

Particularly what I am trying to achieve is for the radio to stay on TX_IDLE state, as the board only serves to transmit packet on command, and I would like the transmission of this packet to happen at the soonest possible duration, without having to go through the entire ramp-up phase at every transmission packet. 

Thanks! 

[ovrebekk]

Hi 

This should be possible, yes. The radio in the nRF52 series is running in a so called 'closed loop mode', which means the radio can be turned on for an unlimited amount of time without problems. 

The main drawback is increased current consumption, but possibly this is not a problem in your design?

Please be aware there is also a fast startup mode available in the nRF52 radio which makes the TX rampup happen in approximately 40us, which is fast enough for most applications. 

Best regards
Torbjørn 

[MATHEUS]

Hi ovrebekk, is there some sample code demonstrating how to keep Radio in TX mode without any issues after one transmission?
We are experiencing some issues when sniffing Empty PDUs from an nRF52 configured to stay in TX_IDLE state and only transmit empty PDUs after 300us. For example, we receive about 4 packets on Wireshark and nothing else after that.

Optionally, do you know more or less the time for nRF52 to switch between RX to TX without going through radio disable. Since fast rump up is a maximum of 40us, I was expecting RX to TX to take something around 20~30us.

[ovrebekk]

Hi

I don't think we have any examples for this unfortunately. All the standard protocols used are based on a TX->RX scenario where you send a packet and then switch to RX in order to receive the acknowledge. 

Did you remember to turn on the external HF crystal before starting the radio? 

Otherwise you will have unreliable radio operation, since the carrier might drift far from the intended frequency. 

Switching from TX to RX should take a similar amount of time as a fast startup, 40us. 

Best regards
Torbjørn

[MATHEUS]

Thanks ovrebekk. I think the issues are somewhat solved. The HF crystal was already turned on

before starting the radio. But I think the issue was handling short inside the interrupt.

Once again, thank you for the amazing support Nordic has been providing over the years.

[ovrebekk]

Hi 

I am happy to hear you found the issue, I will consider the case resolved then. 

The best of luck with your project

Best regards
Torbjørn