Hello,
Using gentoo linux I installed uhd and gnuradio with the commands
“emerge uhd” and “emerge gnuradio”. According to
http://gnuradio.org/redmine/projects/gnuradio/wiki/HowToUse:
“GNU Radio comes with a large variety of tools and programs… The
most commonly used tools include uhd_fft”
Unfortunately I do not have uhd_fft on my system. I do have
uhd_cal_rx_iq_balance, uhd_cal_tx_iq_balance , uhd_images_downloader,
uhd_cal_tx_dc_offset, uhd_find_devices, and uhd_usrp_probe.
According to
http://gnuradio.org/redmine/projects/gnuradio/wiki/InstallingGRFromSource:
“If you want to be able to use USRP devices, you need to install UHD
before installing GNU Radio.”
Questions:
Q1: Why do I not have uhd_fft on my system?
Q2: What is the technically going on that leads to the warning about
installing UHD before gnuradio? What are the consequences of
installing UHD after GNU Radio?
Q3: Which package provides the file uhd_fft: GNU Radio, UHD, or
something else?
Thank you,
Chris
On 03/16/2014 03:20 PM, Chris S. wrote:
uhd_cal_rx_iq_balance, uhd_cal_tx_iq_balance , uhd_images_downloader,
uhd_cal_tx_dc_offset, uhd_find_devices, and uhd_usrp_probe.
According to
http://gnuradio.org/redmine/projects/gnuradio/wiki/InstallingGRFromSource:
“If you want to be able to use USRP devices, you need to install UHD
before installing GNU Radio.”
Questions:
Q1: Why do I not have uhd_fft on my system?
I can’t answer that one
Q2: What is the technically going on that leads to the warning about
installing UHD before gnuradio? What are the consequences of
installing UHD after GNU Radio?
If you’re building from source, the source-build needs to know where UHD
is installed on your system before it can build gr-uhd, since gr-uhd
links again UHD libraries. It can’t very well do that until UHD has
already been installed…
Q3: Which package provides the file uhd_fft: GNU Radio, UHD, or something else?
It’s part of gr-uhd/apps
On Sun, Mar 16, 2014 at 12:48 PM, Sylvain M. [email protected]
wrote:
Since you’re using gentoo, I think the most likely scenario is that
the ‘wx’ USE flag is disabled.
Sylvain,
Thank you for your help. Turns out I the wxwidgets USE flag us set…
but the uhd USE flag was unset. Rebuilding now, but I’m sure this
will fix the problem. BTW, as you might guess, the uhd USE flag
causes net-wireless/gnuradio to bring in net-wireless/uhd. I should
have known something was up when I had to manually emerge uhd.
Chris
Q1: Why do I not have uhd_fft on my system?
Since you’re using gentoo, I think the most likely scenario is that
the ‘wx’ USE flag is disabled.
uhd_fft is a python WXwidget application, so if you disabled this, you
will not have it.
Cheers,
Sylvain
On 03/16/2014 05:06 PM, Chris S. wrote:
Chris
The nice thing about distribution-specific idioms is…there’s too
damned many from which to choose. 
People often criticize build-gnuradio because it “doesn’t cover my
particular distribution”, as if adding support for a new distrib
is as easy as dumping Nigerian spam in your junk folder…
One of Linux’ most serious weaknesses has emerged from its most profound
strength–there are now dozens of distribs extant, each
with their own peculiar packaging tools, idioms, and filesystem
layouts, and with that, troubleshooting strategies. If I were in charge
of
the world, there would only be one Linux distribution 
On 03/16/2014 05:06 PM, Chris S. wrote:
rebuilding now but I’m sure it will work correctly.
Just to confirm, is everything working properly for you now, Chris?
Thanks,
Zero_Chaos
Radio Herd
Gentoo Linux
On Sun, Mar 16, 2014 at 12:31 PM, Marcus D. Leech [email protected]
wrote:
If you’re building from source, the source-build needs to know where UHD is
installed on your system before it can build gr-uhd, since gr-uhd
links again UHD libraries.
Marcus,
Thank you. In gentoo speak, what you said typically translates to
“The gnuradio ebuild has a uhd USE flag. Make sure the uhd USE flag
is enabled.” Well, I checked and sure enough it was disabled. I’m
rebuilding now but I’m sure it will work correctly.
Thanks again,
Chris
On Mon, Mar 17, 2014 at 3:19 PM, Rick F. [email protected] wrote:
Just to confirm, is everything working properly for you now, Chris?
Yes, with the portage mods below:
package.keywords:
~net-wireless/gnuradio-3.7.3 ~amd64
~dev-python/pyqwt-5.2.0 ~amd64
~dev-libs/boost-1.53.0 ~amd64
~dev-util/boost-build-1.53.0 ~amd64
~net-wireless/uhd-3.7.0 ~amd64
package.use:
net-wireless/gnuradio grc uhd examples
Also, it took me a while to figure out that the UHD examples were
zipped up and placed at /usr/share/doc/gnuradio-3.7.3/examples/
Thank you,
Chris
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Hi George,
practical implementation aside: Thanks to Parseval’s theorem, looking
at relative signal strength in frequency and time domain is equivalent.
You can just use a number sink or time sink with a low pass filter to
visualize the received signal power of the carrier. If you’re feeling
like doing things completely right, you can automatically fine tune to
the carrier by using PLL carrier tracking 
As for implementation: there is the max block. What you could do is:
PLL → low pass → complex to mag → integrate → stream to vector →
max/argmax (depends on what you actually want to do)
but that will not “update” your maximum during runtime but only find
the maximum within a vector.
However, implementing an “always output the (abs)maximum float value”
block is really easy as a python block - in fact, doing that might be
a great start into developing GNU Radio blocks. Doing it somewhat
optimized might need some thought, though
Greetings,
Marcus
PS: please make sure not to respond to previous posts when bringing up
a new topic; otherwise, your post will appear in that thread and is
more likely to be ignored.
On 20.03.2014 16:05, George S. Williams wrote:
signal but can’t figure out how to measure the peak. Any advice
would be appreciated.
Thanks, George
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I imagine this is doable, but between experimenting and Google I have
not been able to find a solution. The application is fairly simple- a
FCD is connected to a QT GUI Sink. The FCD is tuned to the pilot
frequency of a ATSC television channel. The attached image shows the
resulting spectrum. The application is intended to assist in pointing an
antenna to receive television broadcasts in a rural area.
What I would like to do is measure the peak and display a number that
represents its level. I have been able to average the entire signal but
can’t figure out how to measure the peak. Any advice would be
appreciated.
Thanks,
George