I specifically need to receive the signal coming from an NFC communication. The carrier wave is at 13.56MHz. However, I need to demodulate the card signal, whose subcarrier is at 13.56MHz+/-847.5MHz = 14.4075MHz, 12.7125Mhz.
The problem is there seems to be a lot of noise at 14.4MHz coming from the dongle as stated here as well: http://superkuh.com/rtlsdr.html.
I have tried the experimental drivers and no-hardware mod without success in demodulating the card consistently (sometimes I had luck and got a good signal). As the matter of facts, I performed HF hardware mod and I can correctly receive the reader consistently but not the card, whose signal is weak/noisy.
There is someone on youtube who managed to demodulate both the card and reader by using the experimental drivers and a home made antenna but I tried two dongles, using the same acquisition chain, without success (noeelec smart and a chinese version):
- https://www.youtube.com/watch?v=wGBXTrt1_vk&t=323s: NFC decoding with Universal Radio Hacker
- https://www.youtube.com/watch?v=2PxpHsa724w: reader and card signal acquisition
- https://www.youtube.com/watch?v=KHfLxwMC5So&t=334s: reader signal acquisition
My questions are:
I have read that a baloon of 4:1 between the antenna (I will post an image of my setup) and the RTL2382U could help acquiring HF signals with direct sampling but not in my case (maybe I did it wrong).
Is there a way to avoid receiving noise from the dongle at 14.4MHz, which could help in demodulating the card? I have seen that changing the crystal oscillator (28.8MHz) is not possible and I believe noise comes from it.
Things which yield to the same result:
- home made antenna or DPL-FANT antenna (13.56MHz antenna)
- wire between q pin and antenna core
- capacitor of value 100nF between q pin and antenna core
- baloon 4:1 between q pin and antenna
Any suggestion is welcome.
Thanks a lot!