Simple WBFM Transmitter - How to configure the USRP1 block to transmit?

Hello guys,

I did the FM receiver (WBFM) based on the link bellow. It’s working
good. I
can tune the local FM stations.

http://www.youtube.com/watch?v=KWeY2yqwVA0

  1. Now I’m trying to build the FM transmitter. My model is attached to
    the
    email. It seems it’s working because I can see the graphical sink.

  2. My major doubt is about how to use the ‘‘UHD: USRP Sink’’, because
    it’s
    dificult to test this block. I don’t know if I set the parameters
    correctly.

  3. The ‘‘UHD: USRP Sink’’ block is different in:
    http://www.dl8rds.de/index.php/Datei:GnuRadio_USRP2_FM_TRX.jpg. The
    ‘‘USRP
    Sink’’ block in this example has additional options like:
    ''Interpolation,
    ‘‘Side’’, ‘‘Transmitt’’. Is my ‘‘UHD: USRP Sink’’ updated or outdated ?

  4. I don’t know if we have to use diferent blocks for USRP1 or USRP2. Do
    we
    have to use ?

  5. The center frequency I’m trying to send the signal is the 105,5 MHz.
    I
    think I’m receiving the carrier 105,5 MHz, because I can hear a tone and
    see
    a signal peak centered in 105,5 MHz in the graphic in the FM receiver
    model.

Thanks for any clue.

Regards,

Bruno C.

WBFM_transmitter_Bruno.grc
http://gnuradio.4.n7.nabble.com/file/n42489/WBFM_transmitter_Bruno.grc


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On Sun, Jul 14, 2013 at 8:27 PM, Bruno C. [email protected]
wrote:

email. It seems it’s working because I can see the graphical sink.

  1. I don’t know if we have to use diferent blocks for USRP1 or USRP2. Do we
    have to use ?

From the image you sent, it looks like you’re using an older version
of GNU Radio before we switched to using the UHD. I would recommend
updating your version and using the UHD interface to the USRPs since
it’ll make things a lot easie, and since we’re all used to that now,
it’ll help us understand and answer your questions.

If you use the UHD, you can use the same block for any USRP device.
Using the older versions will require you to have different blocks for
the USPR1 as the USRP2.

In general, for things like this, make sure that your sample rates
match all the way down the line. So if your signal into the USRP sink
is at 640 ksps, make sure that the USRP device is expecting that rate.
If you’re using the UHD, you’ll just set the sample rate. If you’re
using the older version, you need to understand what the transmitter’s
DAC rate is and figure out the interpolation value from 640 ksps to
meet the DAC rate.

Also, to test, if you have something else, like another USRP or other
GNU Radio front end device (RTL-SDR for example), you can use a simple
FFT program (like uhd_fft) to see the spectrum and see if you’re
getting any signal out of the device.

  1. The center frequency I’m trying to send the signal is the 105,5 MHz. I
    think I’m receiving the carrier 105,5 MHz, because I can hear a tone and see
    a signal peak centered in 105,5 MHz in the graphic in the FM receiver
    model.

That’s definitely a good start.

Tom

The image I sent is not my model. My model was attached to the email.
Have
you seen it?

The image is an example I saw and I noted it’s diferent from my.

My model WBFM_transmitter_Bruno.grc shows a ‘‘UHD: USRP Sink’’. In the
example
http://www.dl8rds.de/index.php/Datei:GnuRadio_USRP2_FM_TRX.jpg,
the USRP Sink is diferent and it has parameter (Interpolation: 200,
Side: B,
Transmit: Enable) my model doesn’t have.

In GRC I have just a single block ‘‘UHD: USRP Sink’’ I belive it is for
USRP1 and USRP2.

I have a FM receiver working fine. I can see and tuning the local FM
stations. But from my FM transmitter I can detect only the carrier.

I attached my model again,
WBFM_transmitter_Bruno.grc
http://gnuradio.4.n7.nabble.com/file/n42573/WBFM_transmitter_Bruno.grc

If you have a time, take a look on that.

Regards,

Bruno


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On Thu, Jul 18, 2013 at 11:59 PM, Bruno C. [email protected]
wrote:

In GRC I have just a single block ‘‘UHD: USRP Sink’’ I belive it is for
USRP1 and USRP2.

Yes. If you are using the UHD sink, it will be the same block for any
USRP device.

I have a FM receiver working fine. I can see and tuning the local FM
stations. But from my FM transmitter I can detect only the carrier.

I attached my model again,
WBFM_transmitter_Bruno.grc
http://gnuradio.4.n7.nabble.com/file/n42573/WBFM_transmitter_Bruno.grc

If you have a time, take a look on that.

Sorry, I don’t have time. Keep in mind my earlier suggestion about
matching the sample rates all the way through your flowgraph.

Regards,

Bruno

Tom

Hi Tom,

I tried to follow your tips but the FM transmitter is not working yet.
Here
is the file: WBFM_transmitter_Bruno2.grc
http://gnuradio.4.n7.nabble.com/file/n42845/WBFM_transmitter_Bruno2.grc

I’m matching the sample rates all the way through my flowgraph.

I’m also using the USRP1 through the ¨UHD: USRP Sink¨ block with a 250k
sample rate, which is a rate that’s supported both by N2XX family and
USRP1/B100 family.

There is something missing yet.

Thanks for your help.

Bruno


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On Tue, Jul 30, 2013 at 10:35 PM, Bruno C. [email protected]
wrote:

USRP1/B100 family.

There is something missing yet.

Thanks for your help.

Bruno

Bruno,

  1. You don’t need a throttle block. A throttle is only necessary when
    running without any hardware. You have both an audio sink (running at
    44.1 kHz) and a USRP sink (running at 250 kHz). These are your
    rate-limiting blocks and the throttle is just getting in the way.

  2. You are massively overloading the signal into the USRP sink. That
    signal level should be +/- 1 at the very most. But you’ll want to back
    off from that for linearity reasons. Instead of setting the gain of
    the LPF to 40, create a slider for that that goes from 0 - 1 with 100
    steps. Default it to 0.5. The signal looked very clean that way.


Tom
Visit us at GRCon13 Oct. 1 - 4
http://www.trondeau.com/grcon13

Just to complete the email, here is the FM receiver block diagram:
FM22.grc
http://gnuradio.4.n7.nabble.com/file/n42890/FM22.grc

Regards,

Bruno


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Hi Tom,

I did the modifications and now I have the WBFM_transmitter_Bruno3.grc
http://gnuradio.4.n7.nabble.com/file/n42888/WBFM_transmitter_Bruno3.grc
It’s working. Thank you a lot. I could do an FM broadcast for the first
time
from one USRP1 to another USRP1.

But I have too much noise and I couldn’t listen to it so clear. Could
you
listen to it clear ?

Another thing curious was I could listen to the sound with another USRP1
but
I couldn’t listen with a normal FM receiver (for instance, a normal FM
radio). What’s the diference between the USRP1 and normal FM receiver?

Thanks a lot!!

Bruno


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On Fri, Aug 2, 2013 at 7:10 AM, Bruno C. [email protected]
wrote:

Another thing curious was I could listen to the sound with another USRP1 but
I couldn’t listen with a normal FM receiver (for instance, a normal FM
radio). What’s the diference between the USRP1 and normal FM receiver?

Thanks a lot!!

Bruno

Bruno,

There’s a lot that can happen and a ton of differences between a USRP
and a standard FM receiver. You’re just going to have to play around
with filters, amplitudes, gains, and frequency settings to figure it
out.


Tom
Visit us at GRCon13 Oct. 1 - 4
http://www.trondeau.com/grcon13