nRF905 antenna

[Witek]

Hi,

I have a number of products with nRF905 successfully deployed. Now, I am in a little struggle with a new one. The problem is the signal strength. The other products have a proper antenna connected through SMA connector. Due to real estate limitation I had to change that to a solder in wire. I used a single core copper wire of length ~173mm. Unfortunately the signal from it is a lot weaker.

Would you have any recommendation? Are there any procedures for changing the antenna matching components to better match the antenna I used? I used the recommended components for 433MHz range.

Thanks Witek

[Håkon Alseth]

Hi Witek,

A quarter-wave antenna will be approx. 36 ohms (If you look at it in a theoretical approach) when it's tuned to the correct length, but has no antenna tuner components.

You'll need to add components to your PCB between the 50 ohm output from the nRF and the antenna, preferably a PI-network, and tune your antenna to 50 ohms @ 433MHz using a network analyzer.

Best regards, Håkon

[Witek]

Hi Håkon,

Thanks for your suggestion.

I expected that a matching network is required. I was hoping to use the example circuit given in the datasheet and just make adjustments to the components used for a better match to the antenna, but to do that I need to know a process to follow.

I guess with nRF905 I need a differential to single ended conversion circuit, and then a matching network. Given that, which components in the example circuit should I replace with the PI-network.

I hope I am making sense.

I appreciate you efforts in helping me to come up with a solution.

Thanks Witek

[Witek]

Hi Håkon,

Sorry, I misunderstood you.

Not having any experience with tuning antennas, I need a little help.

Do I understand correctly that to tune the antenna I need to plug the network analyser into the input of the PI-network with the antenna connected and the rest of the circuit disconnected?

Would an antenna vector analyser suffice for this task?

Would you be able to suggest a good application note for this?

Thanks Witek