Re: [Discuss-gnuradio] Questions about the examples

[Eric Blossom]

On Fri, Feb 18, 2005 at 06:00:57PM -0500, Dawei Shen wrote:
> Hi, dear gentlemen
> 
> Some new USRP boards have arrived yesterday and I am planning to do some
> experiments with it, such as FM transmission and reception. However, I
> am still a beginner and hope I could use some existing codes without any
> modification. Because it's still a bit difficult to me to understand the
> code line by line or even modify them.
> 
> I find some examples are provided in folder /python/usrp1/ and /usrp.
> However, I couldn't use them well. 
> 
> First, transmission and reception needs an RF-end, what kind of RF-end
> should I use? An antenna or just a simple copper wire would be enough?
> Should it be connected through the SMA connector? 

wfm_rcv_gui.py will run with only a wire attached to the basic Rx
daughterboard SMA connector closest to the corner.

You should be able to listen to strong broadcast FM stations.
It takes a single argument, the frequency of the FM station in
megahertz.

  $ ./wfm_rcv_gui.py 92.1


> Second, all these examples do not specify how to run it, i.e. the
> arguments I should provide or maybe some other subtle issues. Especially
> for the wfm_rcv*.py and fm_tx4.py...., what arguments or frequency
> should I provide? Do I need to modify anything in the code? Or where
> could I find some hint about how to set these frequency?

Most of them have help.

address@hidden usrp1]$ ./fm_tx4.py --help
usrp: found usrp rev2
audio: using audio_alsa
usage: fm_tx4.py [options]

options:
  -h, --help            show this help message and exit
  -cFREQ, --ddc-freq=FREQ
                        set Tx ddc frequency to FREQ
  -nNCHANNELS, --nchannels=NCHANNELS
                        number of Tx channels [1,4]

with no arguments, fm_tx4.py will transmit on four frequencies spaced
50kHz apart surrounding 29.325 MHz.  If you've got a general coverage
receiver that can demodulate NBFM at 29.325 MHz you should be able to
listen to it.  If you can hear the signal at 29.325, try tuning up and
down in 50 kHz steps.

The -n option specifies how many different channels it transmits on.
Start with -n 1 and work up to -n 6 or until you run out of CPU.

> Third, some examples require the data file, where could I find the
> working data files? fm_tx4.py requires 4 audio data files, where could I
> find such data or how should I construct them? What data format does the
> audio requires?

The data files contain floating point samples of voice at 32kS/sec.
You can create some of your own using

  $ gnuradio-examples/python/audio/audio_to_file.py -r 32k -f file-1.dat
  $ gnuradio-examples/python/audio/audio_to_file.py -r 32k -f file-2.dat


> Fourth, Invalid EEPROM contents is raised when I use the board. Does it
> matter? Could I just ignore it without affecting reception and
> transmission? If not, how could I solve this problem?

Doesn't matter, but can be fixed with the burn-basic-eeprom command
found in CVS at usrp/host/apps/burn-basic-eeprom 

  $ ./burn-basic-eeprom -a

> Finally, I also have some other equipments such as Agilent signal
> generator. Could I connect it the the board via SMA connector?

Definitely.  

Connect your sig gen to the the Basic Rx daughterboard I and/or Q
inputs.  Set up your siggen so that it's putting out a signal at a
couple of megahertz at 1V peak-to-peak.

You should be able to use usrp_fft.py to see the resulting spectrum.

> So many questions..........Hope you won't feel bored about them, but
> they are really important to a beginner such as me to touch gnu radio.
> 
> Thank you very much

You're welcome.

Good luck!

Eric