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[Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter


From: Vincenzo Pellegrini
Subject: [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter
Date: Tue, 11 Nov 2008 08:26:11 +0100

Martin ,
sorry for the delay. My exams seem to have gone well even if it's not
official yet. I also had to do a demo for a company I have a temporary
contract with for developing some gnuradio based gsm-r security
sentinels. Also the demo was smooth. (i already listed the project on
the gnuradio wiki)
so i really hope i'll be able to prepare the 8Mhz stream for you
within the next 2/3 days. Would this still be useful?

2008/11/3, Martin DvH <address@hidden>:
>
> On Mon, 2008-11-03 at 14:13 +0100, Martin DvH wrote:
>>
>>
>>
>> ________________________________
>>
>> >    Van: address@hidden
>> [mailto:address@hidden
>> Namens Vincenzo Pellegrini
>> >    Verzonden: maandag 3 november 2008 0:16
>> >    Aan: Martin DvH
>> >    CC: discuss-gnuradio
>> >    Onderwerp: [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter
>> >    
>> >    
>> >    This is Great... :)
>> >    
>> >    Yup, the playback cannot be smooth because of the wrong throughput,
>> definitely.
>> >    Did you use the USRP1 with interpolation factor = 16 ?
>> Yes I did.
>> >    
>> >    I can prepare a modulated signal with the correct throughput for
>> you.. this is not a problem... :)
>> >    
>> Please do, this would be great.
>> >    what hard disc are you playing your signal back from?
>>
>> Internal 2.5" harddisk of my acer 6930 notebook (Aspire 6930G-734G32BN
>> LX.AVB0X.135)
>> 2.5" 320GB HDD 5400rpm, SATA
> I checked now. It is a:
> Western digital Scorpio 320 GB SATA (WDC WD3200BEVT-22ZCT0)
> 2.5-inch SATA Hard Drive 320 GB, 3 Gb/s, 8 MB Cache, 5400 RPM
>
> Benchmark from tomshardware (h2benchw 3.6):
> http://www.tomshardware.com/charts/2-5-hard-drive-charts/Minimum-Read-Transfer-Performance,687.html
> minimum read transfer rate 33.5 MB/sec
> average read transfer rate 52.2 MB/sec
> maximum read transfer rate 68.2 MB/sec
>
>
>
>> I am not at home right now So I can't check the exact brand and model of
>> the
>> harddisk.
>> It can do around 38 MB/sec so this is just enough (required 32 MB/sec)
>>
>> I also have 4GB of memory in this notebook, so I think it will buffer the
>> complete file.
>>
>> I had to use my notebook because with my desktop PC (ASrock
>> 939-DUAL-SATA2)
>> The USB TX bandwidth is less then 32 MB/sec.
>> (Which is strange because I CAN receive 32 MB/sec)
>> I get UuUuUu on this machine when useing interpolation 16, so unusable.
>>
>> Regards,
>> Martin
>>
>> >    
>> >    regards
>> >    
>> >    vincenzo
>> >    
>> >    
>> >    2008/11/3 Martin DvH <address@hidden>
>>      
>>
>>
>>              Hi,
>>              
>>              > > In fact: 8 complex Msps implement a 7 MHz channel while
>> 9.142857143
>>              > > complex Msps implement an 8 MHz channel.
>>              > > Just try to go as close as possible to such sampling
>> frequency by
>>              > > using USRP2 and let me know what happens... it could
>> turn out that we
>>              > > need a resampler block.
>>              > So if I use a fractional rate resampler with interpolation
>> factor
>>              > 10/8=1.25 I get a 7 Mhz channel with 10 Msps samplerate.
>>              > If I use a fractional rate resampler with interpolation
>> factor
>>              > 10/9.142857143=1.09375 I get a 8 Mhz channel with 10 Msps
>> samplerate
>>              >
>>              > If I use a fractional rate resampler with DECIMATION
>> factor
>>              > 9.142857143/8=8/7=1.142857143 I get a 8 Mhz channel with 8
>> Msps
>>              > samplerate with the out-of-band skirts folded back at the
>> sides.
>>              >
>>              > Would be interesting to see if this last one works with a
>> USRP1.
>>              >
>>              > I'll let you know how the experiments go.
>>              
>>              I resampled and scaled your ofdm_40.dump file so it now will
>> use 8 Mhz bandwidth with a 8 Msps samplerate.
>>              The reception never can be perfect this way but it seems
>> good enough for
>>              tests.
>>              
>>              My USB DVB-T receiver receives the transport stream without
>> problems.
>>              Mplayer playes the stream without problem for two loops and
>> then crashes
>>              with a broken frame.
>>              My standalone settopbox DVB-T receiver now also receives the
>> stream.
>>              (8 MHz channel on UHF)
>>              It has big problems displaying it. Sound is only a chop of
>> sound now and
>>              then and video stops, then runs for a second, then stops
>> again.
>>              
>>              I think this is because the timestamps and framerate
>> (playout speed)
>>              don't match the data throughput of the MPEG stream anymore.
>>              (It is getting the stream too fast)
>>              
>>              I put my resampled RF file at:
>>      
>> http://www.olifantasia.com/projects/gnuradio/mdvh/OTA/DVB-T/ofdm_40_bw8Mhz_s
>> amplerate_8Msps_cshort.raw
>>              
>>              format is complex signed short integers (I 16 bit, Q 16 bit)
>> at 8
>>              Msamples/sec.
>>              
>>              
>>              Greetings,
>>              Martin
>>              
>>
>>
>>              > > more details will follow as soon as I find some time...
>>              > Thanks and success with your second group of tests.
>>              >
>>              > Martin
>>              > > best regards and greetings
>>              > > to all fellow GNURadioers
>>              > >
>>              > > vincenzo
>>              > >
>>              > > PS
>>              > > Rafael, just have a look back a this thread and you'll
>> find all the
>>              > > info you need to do your test broadcast. Thanks for your
>> interest
>>              > >
>>              > >
>>              > >
>>              > >
>>              > >
>>              > >
>>              > > 2008/10/31 Martin Dudok van Heel
>> <address@hidden>
>>              > >         Hi Vincenzo.
>>              > >         How are things going with your exams.
>>              > >
>>              > >         I hope well.
>>              > >
>>              > >         Thanks for your help so far.
>>              > >
>>              > >         I finally got your DVB-T dump streams working.
>>              > >         I first tried using an undersampled basicTX but
>> never got it
>>              > >         to work.
>>              > >         (use a niquist mirror in the VHF range on
>> channel 11 or 12
>>              > >         (219.5 Mhz or 226.5 Mhz))
>>              > >
>>              > >         I now use a RFX900 and that works with a
>> pinnacle PCTV-Solo
>>              > >         72e usb DVB-T receiver card plugged into my PC.
>>              > >         I use 858.0 Mhz (channel 69)
>>              > >         I used a 10 dB attenuator on the antenna output
>> to limit
>>              > >         output power.
>>              > >         I also modified the RFX900 to enable
>> transmitting outside of
>>              > >         the ISM band. (disable saw-filter. add 220 pF
>> capacitor)
>>              > >
>>              > >         Apparantly the pinnacle 72e can receive 7 Mhz
>> channels on the
>>              > >         UHF channels.
>>              > >         My standalone settopbox DVB-T receiver can't
>> handle it.
>>              > >
>>              > >         I noticed you don't use the full possible range
>> in your 16 bit
>>              > >         streams.
>>              > >         (only goes from -80 to +80 while you could use
>> -8192 to 8192)
>>              > >         Is this on purpose?
>>              > >         I can multiply samples by 64 and get a cleaner
>> signal. (But
>>              > >         also more output power)
>>              > >
>>              > >
>>              > >         I do have a request, I hope it is not too much
>> work.
>>              > >         Could you make a stream with 10 Msamples/sec
>> samplerate and 8
>>              > >         Mhz wide channel.
>>              > >         This way I can use standard standalone DVB-T
>> receivers and
>>              > >         don't have the 7Mhz bandwith on UHF problem.
>>              > >
>>              > >         For the 10 Msps stream I would have to use my
>> USRP2 to output
>>              > >         it.
>>              > >         It has a 100 Mhz DAC (in stead of 64 Msps in the
>> USRP1)
>>              > >         It has a gbit ethernet connection for the
>> samples, so I can go
>>              > >         up to 25 Msps.
>>              > >         It can only do fixed interpolation rates so I
>> have to choose
>>              > >         from the table below.
>>              > >         (8 Msamples/sec is not supported on the USRP2)
>>              > >
>>              > >
>>              > >         USRP2
>>              > >         dac_rate        interp  ethernet_sample_rate
>>              > >         100             4       25
>>              > >         100             5       20
>>              > >         100             6       16.67
>>              > >         100             7       14.29
>>              > >         100             8       12.5
>>              > >         100             9       11.11
>>              > >         100             10      10      <----I think 10
>> Msamples/sec
>>              > >         should be optimal
>>              > >         100             11      9.09
>>              > >         100             12      8.33
>>              > >         100             13      7.69
>>              > >         100             14      7.14
>>              > >
>>              > >
>>              > >         I think 10 Msamples/sec would be a good
>> candidate.
>>              > >
>>              > >         Have you also tried using 8 Msamples/sec on the
>> USRP1?
>>              > >         I know there would be no room left for IF
>> channel filtering,
>>              > >         but it could in theory still work.
>>              > >         If this works I would also very much appreciate
>> a 8Mhz
>>              > >         bandwidth stream with 8 MSPS samplerate so I can
>> demonstrate
>>              > >         with a standard USRP1.
>>              > >
>>              > >         Thanks for your help so far.
>>              > >         I appreciate it very much.
>>              > >
>>              > >         And good luck with your exams.
>>              > >
>>              > >         Have a nice weekend.
>>              > >
>>              > >         Greetings,
>>              > >         Martin
>>              > >
>>              > >
>>              > >
>>              > >
>>              > > --
>>              > > Vincenzo Pellegrini
>>              
>>              
>>
>>
>>
>>
>>      --
>>      Vincenzo Pellegrini
>>      
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> Discuss-gnuradio mailing list
>> address@hidden
>> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>
>
>


-- 
Vincenzo Pellegrini




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