Two Channel Diversity Receiver with NRF24L01

Wireless & IoT
1

I’m using “Transceiver nRF24L01+ Module with RP-SMA” in an application that simply looks for the IRQ output of the nRF24L01 going active to create a trigger signal at the receiver.

I’m having issues with missed triggers, maybe because of RF interference. I had absolutely no issues on channel 70 (2.470 Ghz) while a second transimitter/receiver on channel 66 (2.46 Ghz) varied in reliability for missing 1 of 10 triggers to missing nearly all triggers on the third day of a large event. I cannot reproduce the issue on the workbench.

I’m thinking about using two transceivers on different frequencies to reduce the probability of an RF collision on a trigger event. The IRQ outputs of two separate receivers would be logically or’ed to create a single trigger.

I’m trying to decide if I should share a single antenna, or use a separate antenna for each receiver. I have several questions:

  1. Two transmitters and receivers per wireless trigger for frequency diversity. Is this a good idea? Why or why not?

  2. Should I use a single antenna shared between two receivers? If I do, do I need to modify the tank circuit components?

  3. Latency is a critical consideration–the application can tolerate only a few milliseconds of delay between trigger input at the transmitter and trigger output and the receiver. But, if it would help improve reliability of the receiver trigger input, I could trigger on two transmitters sequentionally, instead of simultaneously. Would this be recommended?

  4. Are there pairs of frequencies that would be recommended for maximum “diversity”?

Thanks,

Dave Thomas

2

Before adding a second radio device, have you considered implementing a frequency hopping protocol? You can use the CD/RPD bit to tell if there is considerable traffic on a channel, and then switch channels to a less used channel. This could be synchronized by messaging from one device to another before changes, or by dwell time on a certain channel. The nRF24Z1 uses a similar protocol, but it’s built into the hardware.

3

Yes, I’ve considered this, but a bit simpler approach to start with–I just added some code to recognize commands to switch RF channels. I’ll separately monitor the frequency band utilization using a PC and remotely configure both transmitter and receiver to use the best available channels.

I thought I’d do both–add two receivers and make their RF frequency remotely programmable.

Thanks,

Dave Thomas