Quadrature demodulator output on GPIOs

[Reinhard]

Hi,

the product specification of the nRF51822 states the possibility to carry quadrature demodulator signals on GPIO pins. This would let one allow to observe the physical transmission before (de-)whitening etc. Is there an example project /code for this?

Thanks, Reinhard

[Øyvind Karlsen]

Hi Reinhard,

I'm not sure that I understand your question correctly, but I'll attempt to answer as best I can.

We do not route the on-air-signal before demodulation from the radio out to pins, furthermore that signal is not coded in quadrature.

The quadrature decoder is suitable for mechanical and optical sensors, as well as motors, i.e. wired interfaces. I am not sure what you want to use whitening for in this context.

Best regards,

Øyvind

[Reinhard]

Hi Øyvind,

ok I think we mixed up to completely different blocks, maybe due to the similar wording. I was not interested in the quadrature decoder (for sensors etc.), but the demodulator of the radio signal (likely a quadrature demodulator producing I/Q data).

In the RADIO block diagram (Figure 17 in the reference manual) there are the 2.4GH RX/TX blocks which are connected to dewhitening/whitening blocks, resp. This connection should carry the raw baseband signal after demodulation (in case of RX), right? I'd be interested in these signals and thought they could be routed outside because of the statement in the product spec (page 30).

All pins can be individually configured to carry serial interface or quadrature demodulator signals.

[Øyvind Karlsen]

Hi,

For this context the decoder and demodulator are the same thing. We do not use quadrature decoding of our on-the-air signal, the encoding is FSK(Frequency shift keying), specifically GFSK(gaussian FSK), which is FSK passed through a gaussian filter. If you want to view this signal like it looks on the air, you can use a packet sniffer or spectrum analyzer.

More info on FSK can be found on wikipedia.

[Reinhard]

Hi,

okay, I thought the FSK (de-)modulation is performed by a quadrature (de-)modulator. So if I understood you correctly, it isn't possible to bring the nRF51 to a "packet sniffer like" mode.

Thank you for your explanations.

[Øyvind Karlsen]

If you want to do packet sniffing have a look at nRF Sniffer =)