WBX and frequencies around 433 MHz?

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

On Mon, Dec 5, 2011 at 10:50 AM, Patrik E.
[email protected] wrote:

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.

What does the FFT of the received data look like at 433MHz? 420MHz?

–n

Br,
Patrik

Well, there’s a lot of amateur radio traffic in that frequency range,
which may be interfering.

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?


Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

the 430-440 MHz region the reception fails.

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.

-Patrik

example 2 GHz, 1.5GHz, 800MHz, 500MHz, 420MHz. If I tuned the

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

didn’t work. After checking my code several times I decided
cable and 20 dB attenuator.

Patrik
USRP2s, so I wouldn’t expect any interference from other systems.

This looks like horrendous phase noise.

What base platform is this? (USRP1, USRP2, N2XXX, etc)

Do you have multiple base platforms you can try this on, and if so, are
the results the same?


Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

Patrik,

Can you please check to see that the WBX LO is locked? If you have a
GRC flowgraph, you can use a function probe block with the following
settings:

ID: lo_locked
Block ID: uhd_usrp_source_0 (or whatever your UHD source block is
named)
Function name: get_dboard_sensor
Function args: ‘“lo_locked”, 0’
Poll rate: 1

Then use a WXGUI checkbox with a default value set to bool(lo_locked).
When you run your flowgraph, the checkbox will indicate whether the LO
is locked.

In your own non-GRC application you can use .get_dboard_sensor(“lo_locked”, 0) to check the status of the
daughterboard LO lock.

–n

On Tue, Dec 6, 2011 at 4:40 AM, Patrik E.

Nick,

I tuned the center frequency to 400 MHz, 430 MHz and 433 MHz and the LO
is locked for all of them.

The spectrum for 430 MHz looks like the spectrum for 433 MHz (white
line) in my previous post. I’ve tried the same thing on another USRP2
with another WBX and I get similar spectrums. So it doesn’t happen on
just one device.

BTW, I like the probe block, didn’t know it before. It can be useful for
other purpose aswell.

Br,
Patrik

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