Re: [Discuss-gnuradio] Simple WBFM Transmitter - How to configure the USRP1 block to transmit ?

[Tom Rondeau]

On Sun, Jul 14, 2013 at 8:27 PM, Bruno Cardoso <address@hidden> wrote:
> 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 Is my ''UHD: USRP Sink'' updated or outdated ?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 ?

>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.


> 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.

That's definitely a good start.

Tom


>
> Thanks for any clue.
>
> Regards,
>
> Bruno Cardoso