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[Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter
From: |
Martin DvH |
Subject: |
[Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter |
Date: |
Sun, 02 Nov 2008 23:53:40 +0100 |
Hi Vincenzo,
On Sun, 2008-11-02 at 01:28 +0100, Vincenzo Pellegrini wrote:
> Hi Martin,
> sorry for the delayed replies but now I've passed my first cluster of
> PhD tests (went well)
Congratulations.
> and I've got to carry out some work + preparing the second group of
> tests.
Success.
> Well, really glad to know that you managed to receive my signals.
> Yup dvb-t sticks can actually receive 7 MHz channels everywhere,
I found that some of them need special "australian 7MHz at UHF" firmware
to get this to work.
Luckily my DVB-T usb stick doesn't need this trick.
> Well, actually any DVB-T chipset can but typically manufacturers
> impose strange limitations on set-top-boxes such as "7 MHz chanels
> accepted only in VHF" I don't really know why.
>
> The signal I provided you with is suitable for both 7 and 8 MHz
> channels without any modification needed. The only thing you have to
> do is to set your sampling frequency a bit higher. this should be
> possible with USRP2.
The receiver might still have a problem that it is getting in the MPEG
streams at a higher rate then realtime.
> 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.
> 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
- [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter, Vincenzo Pellegrini, 2008/11/01
- [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter,
Martin DvH <=
- [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter, Martin DvH, 2008/11/02
- [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter, Vincenzo Pellegrini, 2008/11/02
- RE: [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter, Martin DvH, 2008/11/03
- RE: [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter, Martin DvH, 2008/11/03
- [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter, Vincenzo Pellegrini, 2008/11/11
- Re: [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter, rafael2k, 2008/11/11
- [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter, Vincenzo Pellegrini, 2008/11/11
- Re: [Discuss-gnuradio] Re: Soft-DVB DVB-T transmitter, Martin DvH, 2008/11/14