Re: RFID using LFTX/LFRX (Was [Discuss-gnuradio] GNU Radio mention in DEFCON subway presentation)

[ChoJin]

On Sep 7, 2008, at 6:58 AM, Michael Ossmann wrote:

> On Sun, Sep 07, 2008 at 02:02:35AM +0200, ChoJin wrote:
> > I tried a very simple test:
> > - two loops of wire, one for the LFTX (A slot, antenna TXA) and one  
> > for
> >  the LFRX (slot B, antenna RXB)
> > - generating the sinus wave using usrp_siggen.py -f 0 --sine -w  
> > 13.56e6
> > - trying to detect this sinus back using usrp_fft/usrp_oscope
> >
> > I put my two loops of wires as close as possible from each other  
> > but I
> > just can't detect my sinus wave back at all.
>
> I think the -w option is outside of your transmit bandwidth.  Try:
>
> # usrp_siggen.py -f 13.5e6 --sine -w 60e3
>
> Also, are you sure that you are receiving on the correct slot and
> antenna port?

Thanks, it actually worked,
I had to use -f 13.50 --sine -w 60e3 to get my signal at 13.56Mhz  
though.

I can now see my signal, but I don't get any sideband channels.
So either my loop of wires is not correct (I actually did it "randomly",
do you have an exact formula for the number of loops vs. diameter?)
or I'll have to really implement the pulses instead of a simple sine  
signal.

By the way, I'm a little bit confused about the meaning of the antenna  
slots
on the LF*X boards. Why do we have two slots for the antenna?
I'm currently using the antenna slot A for the LFTX plugged in the  
slot A
and the antenna slot B for the LFRX plugged in the slot B, but I'm not  
sure
that's what I was supposed to do.

--
Best Regards,
ChoJin