Re: [Discuss-gnuradio] Basic USRP AM Transmission

[Martin Dvh]

Robert Roberts wrote:
> 
> ----- Original Message -----
> From: Martin Dvh <address@hidden>
> Date: Monday, April 17, 2006 3:06 pm
> Subject: Re: [Discuss-gnuradio] Basic USRP AM Transmission
> 
>>Robert Roberts wrote:
>>
>>>Hello everyone,
>>>
>>>
>>>I have been experimenting with the Flex400 board and have been 
>>
>>trying to
>>
>>>implement a basic AM transmitter. I have a WFM and NFM transmitter
>>>working, but I cannot get the AM one to transmit correctly.   The 
>>
>>code> below generates a much higher frequency tone.  Any advice to 
>>what I am
>>
>>>doing wrong?   Does my output need filtering before connecting to 
>>
>>the> sink?     
>>
>>>
>>>self.u = usrp.sink_c ()       # the USRP sink
>>>
>>># Code here for setting up the USRP, omitted
>>>
>>>src = gr.file_source (gr.sizeof_float, "audio-1.dat", True) # 
>>
>>440Hz tone
>>
>>>file
>>
>>What is the sample_rate of the audio file
>>What is you interpolation rate of the usrp
>>What is the duc frequency of your usrp.
> 
> 
> I have the file source sampled at 32kS/s
> 
> I use the following code for setting up my usrp:
> 
>         self.dac_rate = self.u.dac_rate()                    # 128 MS/s
>         self.usrp_interp = 400
>         self.u.set_interp_rate(self.usrp_interp)
>         self.usrp_rate = self.dac_rate / self.usrp_interp    # 320 kS/s
>         self.sw_interp = 10
>         self.audio_rate = self.usrp_rate / self.sw_interp    # 32 kS/s
> 
>         # determine the daughterboard subdevice we're using
>         if options.tx_subdev_spec is None:
>             options.tx_subdev_spec = usrp.pick_tx_subdevice(self.u)
> 
>         m = usrp.determine_tx_mux_value(self.u, options.tx_subdev_spec)
>         self.u.set_mux(m)
>         self.subdev = usrp.selected_subdev(self.u, options.tx_subdev_spec)
>         print "Using TX d'board %s" % (self.subdev.side_and_name(),)
> 
>         self.subdev.set_gain(self.subdev.gain_range()[1])    # set max
> Tx gain
>         self.set_freq(options.freq)
>         self.subdev.set_enable(True)                         # enable
> transmitter
> 
> 
> This is the same code I used for both a NFM and WFM transmitter, both of
> which appeared to transmit without problems.
But do you actually put a software interpolator in there somewhere.
I didn't see any in your code:
>>>self.connect (src, const)
>>>self.connect (const, conv)
>>>self.connect (conv, gain)
>>>self.connect (gain, self.u)
should be:
self.connect (src, const)
self.connect (const, conv)
self.connect (conv, gain)
self.connect (gain, softwareinterpolator)
self.connect(softwareinterpolator,self.u)

greetings,
Martin
> 
> Sincerely,
> ~Chris~
> 
>>If the sample rate of your audio file is for example 48000 Herz
>>Then the usrp interpolation rate should be 128000000/48000 = 2666
>>Which is I think way out of range for the usrp
>>You first have to interpolate in software to something in the range 
>>of the usrp.
>>
>>Greetings,
>>Martin
>>
>>>const = gr.add_const_ff (1.0)
>>>conv = gr.float_to_complex()
>>>
>>>               
>>>gain = gr.multiply_const_cc (4000.0) # transmitter gain
>>>
>>># connect it all
>>>
>>>self.connect (src, const)
>>>self.connect (const, conv)
>>>self.connect (conv, gain)
>>>self.connect (gain, self.u)
>>>
>>>
>>>
>>>
>>>Thanks,
>>>~Chris~
>>>
>>>
>>>
>>>
>>>_______________________________________________
>>>Discuss-gnuradio mailing list
>>>address@hidden
>>>http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>>
>>
>>
>