DVB-T 6, 7 or 8 Mhz Channels ?

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G4GUO
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Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by G4GUO » Mon May 03, 2010 9:09 pm

Hello Ken,

I was thinking just this afternoon that I should post a block diagram.

The system is similar to the one M0DTS is using. However I have been
gradually replacing the modules he is using with my own. It was useful
to have a working system to use as a reference.

The output of the camera is captured with a Hauppauge PVR500 PCI card.
These cards are pretty cheap now used on eBay.
The PVR500 is a dual channel version of the PVR150. My code then extracts
the Program stream coming from the card, turns it into a transport stream.
Adds the various required SI table transport packets.
I then apply the scrambling, Reed Solomon coding, punctured convolutional
coding and interleaving. I then map the dibit stream into IQ symbols and
apply a compensated root raised cosine filter. The resulting IQ samples are sent to the
USRP2 over a 1Gb Ethernet connection where they are upconverted to the final transmit frequency.
I have done a similar thing for the DVB-T waveform but it has a much more complex
format and I have not got around to testing any of that yet.

So to answer your question my code does everything except the hardware MPEG
encoding (PVR500), the D to A conversion and frequency up-conversion (USRP2 +WBX).

Being software of course I hope to add many more facilities (when I have figured
a bit more of the specs, they are a bit hard going).

The WBX produces about 100 mW on any frequency between 50 MHz and 2.2 GHz.
It is a shame it does not cover 13cms although Ettus Research has boards that
do. I met Matt Ettus N2MJI at a TAPR convention in 1999 he was a very young
student then, he has done well for himself.

- Charles

KenW6HHC
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Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by KenW6HHC » Wed May 05, 2010 4:07 pm

Hi Charles G4GUO,

Thanks for adding the Block Diagram of your DVB-T DATV set-up to your blog.

My problem was that I had not become familiar with the USRP2 SDR unit details (or even an overview), so everything was fuzzy in my mind. Your Block Diagram clears up all of the functions nicely.

My best wishes for success on your project....and keep that blog going.

Best regards....de Ken W6HHC

G4GUO
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Joined: Tue Feb 16, 2010 12:51 pm

Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by G4GUO » Wed May 05, 2010 5:05 pm

Hi Ken,

I enjoyed your DATV item in the PSR. I also read with interest the item you
mentioned about the DATV repeaters.

The diagram is of DVB-S at the moment, when I have intergrated the DVB-T code
I will add those modules to the diagram. The scrambling and FEC are common
to both systems. DVB-T has a couple of extra interleavers and of course uses
OFDM.

Yes the world of USRPs is very murky. The USRP is designed to work
with the GNURadio software architecture. GNURadio is a set of standard signal
processing libraries which you can chain together using the Python language.
There is an ATSC decoder for GNURadio along with some other stuff.
Most people using the units seem to be academics playing with new Wifi protocols.

I am not actually using GNURadio. To be honest the documentation is a bit
lacking and it was quicker for me to roll my own.

I don't have much to report at the moment as I have been making up some
semi-rigid cables for the PA. I will keep up the blog until I run out of DATV stuff.
Then I may start blogging about something else. I thought of having a go
at implementing D-Star on the USRP2 after DATV. I already have a D-Star
Dongle that someone donated to me.

- Charles G4GUO

http://www.g4guo.blogspot.com/

KenW6HHC
Posts: 309
Joined: Mon Jun 01, 2009 4:20 pm

Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by KenW6HHC » Tue Jun 01, 2010 9:53 pm

Hi Charles G4GUO,

Just a quick note to let you know that I gemerated an article on DVB-T for DATV for my loacal radio (OCARC) newsletter that will be published in mid-June. I have not found any other article on DVB-T for DATV that has put as much information on DVB-T for DATV in one location.

The article is called:

TechTalk86 - Overview of DVB-T Modulation for DATV

I put a near-final draft of the article up on the OCARC web site at:

www.W6ZE.org/DATV/

I would be interested in any comments on the article.

BTW...I have continued to enjpy following your DVB=T journey on your blog.

73...de Ken W6HHC

G4GUO
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Joined: Tue Feb 16, 2010 12:51 pm

Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by G4GUO » Wed Jun 02, 2010 9:26 am

Hello Ken,

I had a quick read through your article.
At a first glance I did find some rather
pedantic errors. I will drop you an email
about them later in the week.

Interesting about Amateurs only using the
2K mode. I guess that is the advantage of
using an SDR, I don't have the memory space
limitations. Load wise the 8K mode only seems
to increase the CPU loading by a few percent.

I recently downloaded the latest version of
the ETSI DVB-T standard. I notice it now
includes DVB-H, DVB-Handheld which is a
4K mode. I may add it to my code.
First I have to get the current code to be
recognised by my TV receiver!
I think I now have all the extra symbol
and bit interleavers implemented correctly.
I also believe the BCH encoder for the TP information
is correct (but I don't have a test vector for it).

If I can't get the Intel MMX based FFT to work correctly
I will try FFTW (the FFT everyone else uses).

I am hoping to get back to testing at the end of
the week but anyone that reads my blog knows that!

- Charles

G4GUO
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Joined: Tue Feb 16, 2010 12:51 pm

Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by G4GUO » Sun Jun 06, 2010 2:59 pm

I just thought I would let everyone know that I finally
managed to transmit DVB-T using my software and
to receive it on a Samsung TV. The first test was
8K mode QPSK 1/4 guard and 7 MHz channel.

Since the original post I can verify that the 2K
mode works and that QAM16 and QAM64
also work both on 8K and 2K.

- Charles G4GUO

M0DTS
Posts: 685
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Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by M0DTS » Sun Jun 06, 2010 8:56 pm

Congratulations Charles that's great news!!

We need a cheaper version of the USRP2 now ;-)

Keep up the good work.

73

Rob

G4GUO
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Joined: Tue Feb 16, 2010 12:51 pm

Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by G4GUO » Mon Jun 07, 2010 6:34 am

Hi Rob,

Thanks.

Well there is a research team at a University in
Pisa Italy that have done the same thing using a USRP1
which only has a USB2.0 interface so it can be done.
A/D do a range of chips that take an I/Q input
and up convert to 1.3 GHz like the ADRF6702

I think I will leave that to others and concentrate on
getting the EPG and Teletext working. Then maybe
do DVB-S receive (as it is much easier than DVB-T and
of much more use for Amateur Radio).

I have already managed to display my transmitter transport
stream using the Xine media player so if I can get the
received DVB-S signal down to a transport stream I should
be able to display it.

- Charles

G4GUO
Posts: 729
Joined: Tue Feb 16, 2010 12:51 pm

Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by G4GUO » Wed Jul 14, 2010 1:42 pm

It seems it is a choice between 7 or 8 MHz as most
TVs don't support 6 MHz or at least none of the
TV/STBs I have do.

In case anyone is interested I have been doing some tests
with MPEG4 H.264 video over DVB-T. My last generation
HD TV is able to decode H.264 as well as MPEG2. It seems
some countries are using MPEG4 over DVB-T so I guess it
should not have come as a surprise to me.

- Charles

F3YX
Posts: 4
Joined: Tue Jul 27, 2010 10:58 am

Re: DVB-T 6, 7 or 8 Mhz Channels ?

Post by F3YX » Tue Jul 27, 2010 11:17 am

Hello Om's,
I am qrv DVB-T, DVB-C and DVB-S on 70Cm, 24Cm, 13Cm, and 3 Cm. Same for ATV.
For DVB-T on 70 Cm the commercial receivers with 6, 7 or 8 Mhz are not really usable because ISM, FM Repeaters, Pakett aso. Thats why I am using an SR-Systems receiver covering 2, 3, 4, 5, 6, 7, and 8MHZ. With 2MHZ on 437 MHZ and good filtering, there is no qrm (ISM = 30 dB down) But the best results are allways in DBVB-S where quite each day a contact between 250km (F9ZG), 300km (F5AGO) and 400km (F1AHH) can be done. It depends of the selective fading. I have also to say that ATV for Dx and contests is always giving better results as DATV on 70cm (1 MHZ BW enough for contest)
Best 73.
F3YX

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