nRF51422 BLE/ANT+ RF testing with and without modulation

[Chris Uroda]

I am being told by a RF test lab that I need to provide a sample which has the following modes: BLE "with modulation" BLE "without modulation" ANT+ "with modulation" ANT+ "without modulation"

As far as I understand, the BLE "with modulation" is achieved by using the BLE DTM routines. I see a "special" Nordic specific vendor DTM payload type - CARRIER_TEST - which can be used to test BLE without a modulated signal/"continuous carrier signal".

So, the BLE cases seem to be covered.

For ANT, I am aware of the CW test routines which are present, and these are working.

My main question is - what is the best way to test the ANT+ transmission of a modulated signal?

At the moment the only way I can think of is to use the regular sd_ant_broadcast_message_tx routine. I am concerned though that the "duty cycle" will not be high enough - the test lab has requested that duty cycle be as close to 100% as possible.

I am calling the sd_ant_broadcast_message_tx in an infinite loop, with a payload buffer of 8 bytes. I have a cheap 2.4GHz spectrum analyser (www.oscium.com/.../wipry-combo) and it appears that the radiated power is significantly lower than the equivalent ANT CW test. The significantly lower radiated power is making me think that the duty cycle is not as high as it could be - but I might be mistaken.

EDIT - I thought that I was observing a signal from the usage of sd_ant_broadcast_message_tx, however it was from another transmitter in the room. No matter what I try, I can't seem to see a signal on the analyser when using the sd_ant_broadcast_message_tx approach.

Any help will be greatly appreciated!

-Chris

[Håkon Alseth]

Hi Chris,

I know we've already sorted this out through different channels, but I'm going to post the answers here as well, in case someone else wants to know.

BLE part is, as you mention, covered by the DTM firmware. The "ANT+ without modulation" is also covered by the DTM firmware due to:

An unmodulated carrier is independent of the data rate, so it will look the same no matter what data rate you set. The PLL is locked in this mode, so modulation is not possible. It's the same, but it's called different things depending where you see it, ANT CW mode, constant carrier, continuous carrier etc. But the modes are all equal. The only parameters that affects the unmodulated carrier are frequency and output power.

However, "ANT+ with modulation" is not a mode you can set in DTM. Since ANT uses the same modulation as the NRF_1MBIT, we recommend sending modulated packages continuously using the "radio_example" in the SDK, where NRF_RADIO->MODE = NRF_1MBIT.

Best regards Håkon