Re: [Discuss-gnuradio] WBX and frequencies around 433 MHz?

[Patrik Eliardsson]

> > > Hi,
> > >
> > > While I was testing the DQPSK-(de)modulation blocks in GRC. 
> > I found a frequency region where the reception failed. I 
> started with 
> > the ISM-band (433 MHz) as the center frequency, and the reception 
> > didn't work. After checking my code several times I decided 
> to change 
> > the center frequency to 2 GHz and everything started to work. So I 
> > tried several other center frequencies with successful outcome, for 
> > example 2 GHz, 1.5GHz, 800MHz, 500MHz, 420MHz. If I tuned the 
> > frequency to the 430-440 MHz region the reception fails.
> > >
> > > I've used 2 USRP2s with the WBX and connected them with a
> > cable and 20 dB attenuator.
> > >
> > > I have 4 different WBX cards and the result is the same for
> > each of them. 
> > >
> > > Have someone encountered the same problem with frequencies
> > around 433 MHz?
> > >
> > > Br,
> > > Patrik
> > >
> > >   
> > Well, there's a lot of amateur radio traffic in that 
> frequency range, 
> > which may be interfering.
> 
> I will keep that in mind. But I used a cable between the 
> USRP2s, so I wouldn't expect any interference from other systems.
> 
> > Also, there's a special frequency at 433.920MHz used for 
> garage door 
> > openers.  Are you running
> >   your USRP2 with the covers on or off?
> 
> The covers are on.
> 
> I will have a look at the received spectrum again, as Nick suggested. 


Please have a look at the attached spectrum. 

Cable.png shows the spectrum when the transmitter is connected to the spectrum 
analyzer with a cable and 20 dB attenuator. The white line is the spectrum at 
the center frequency 433 MHz and the yellow line is at 400 MHz. The spectrum 
for 433 MHz looks like crap.

Figure 400.png and 433.png shows the received constellation points and the 
received spectrum after a LPF for 400 MHz and 433 MHz.

-Patrik

cable.png
Description: cable.png

433.png
Description: 433.png

400.png
Description: 400.png