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

[Martin DvH]

________________________________

>       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 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