You can use the DTV component in GNU Radio to output a known good OFDM
signal.
There are many DVB-T2 flow graphs in
<install_dir>/share/gnuradio/examples/dtv
Try vv009-4kfft.grc. A link to the test input file can be found in
README.dvbt2.
Depending on which version of UHD you're using, you may have to delete
the parameter "send_frame_size=65536" in the device address.
You should just start to see distortion at a gain setting over 78.
Ron
On 5/9/19 10:03, Michael Deacon via USRP-users wrote:
I hope this is what you are looking for. Would clipping here be an
indication of saturation?
Thanks,
Mike
*From:* Brian Padalino <bpadal...@gmail.com>
*Sent:* Wednesday, May 8, 2019 6:11 PM
*To:* Michael Deacon <micha...@sysware.com>
*Cc:* usrp-users@lists.ettus.com
*Subject:* Re: [USRP-users] Relationship between IQ values, gain and
noise on B205mini transmitter
What does the signal look like in the time domain?
Is it driving the amplifier on the B205mini into saturation?
Brian
On Wed, May 8, 2019 at 7:57 PM Michael Deacon <micha...@sysware.com
<mailto:micha...@sysware.com>> wrote:
I added some attenuation. The overload is gone but the condition
persists.
Thanks,
Mike
*From:* Brian Padalino <bpadal...@gmail.com
<mailto:bpadal...@gmail.com>>
*Sent:* Wednesday, May 8, 2019 4:37 PM
*To:* Michael Deacon <micha...@sysware.com
<mailto:micha...@sysware.com>>
*Cc:* usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>
*Subject:* Re: [USRP-users] Relationship between IQ values, gain
and noise on B205mini transmitter
On Wed, May 8, 2019 at 7:28 PM Michael Deacon via USRP-users
<usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>>
wrote:
Hello,
I have a simple transmitter consisting of a file source
connected to a USRP sink (attached image radio.png). The file
contains interleaved floating point IQ representing a few
seconds of LTE. The IQ amplitude values are normalized between
+1.0 and -1.0. The sink is configured to 60db, 7.5MHz sample
rate, 385MHz center frequency and 5MHz bandwidth. The output
looks exactly like the original on a spectrum analyzer (see
attached good.jpg). If I turn up the gain on the sink or
increase the amplitude of the IQ data I get what looks to be
noise on either side of the signal spectrum (see attached
bad.jpg). Any idea what is going on here?
Your bad.jpg picture has the spectrum analyzer saying OLVD. Try
changing your reference level of the spectrum analyzer to be
higher so you don't saturate the input of the spectrum analyzer.
Tell us if that fixes it for you.
Brian
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