DVB-T 6, 7 or 8 Mhz Channels ?

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

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

Post by G4GUO » Tue Jul 27, 2010 11:35 am

Hi,

I agree, I only intended using DVB-T on 24 cms and above and mainly
for local communications. I am using a simple Homebrew converter
to translate the signal from 24 cms down into the UHF TV band.

I should be starting some MPEG4 HD tests later in the week.

- Charles

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

HDTV

Post by G4GUO » Wed Jul 28, 2010 2:49 pm

I finally managed to get the component video leads
for my camera. Consequently I made my first 1080i
HDTV H.264 transmission this afternoon using DVB-T.
7 MHz channel spacing, 16 QAM, FEC 3/4 and
guard period 1/32. The video rate was 11.2 Mbits/s.
I have never seen HDTV (we don't have terrestrial HD
yet on the South Coast) so I was quite surprised at the quality.

Now that I have that out of my system I can go back to
fiddling with DVB-S!

- Charles G4GUO

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

Rather neat way to transmit DVB-T

Post by G4GUO » Tue Jan 18, 2011 8:33 am

http://bellard.org/dvbt/

I know this is a few years old but the idea has merit.
If only I could figure out how to write the output of my
DVB-T/S code directly to a video card!

- Charles G4GUO

g7lwt
Posts: 32
Joined: Mon Feb 25, 2008 9:33 am

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

Post by g7lwt » Mon Jan 31, 2011 4:57 am

Hi Charles,

somehow I'd missed your earlier posting about DVB-T2 (HD) and now find myself wondering if you have considered looking at DVB-S2? It seems that some future amateur DATV applications may standardise on S2, so as to benefit from lower bandwidth requirements when used for standard definition transmissions.

73 de Darren
G7LWT
PS. Adapting your code for output via a video card would be a very welcome development!

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

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

Post by G4GUO » Mon Jan 31, 2011 8:54 am

Hello Darren,

The HD was sent using DVB-T, my TV was able to decode it. I believe the French transmit
HD over DVB-T so I suspect that is why the TV had no problem.

The biggest problem with S2 seems to be the fact that the majority of receive chipsets
don't operate at the low rates we use. I did find one chipset that appears to and it is
already supported by Linux (AZUREWAVE AD-SP400, STB0899 STB6100 chipset). I could of course
implement the transmit and receive code in software especially at the lower rates, at the higher
rates an FPGA would have to be used. At the moment I can't see how to do that as S2 uses
64800 bit long frames and manipulating those in an FPGA needs some thought.

Yes it would be nice to marry my code with the video card approach I looked into that a while ago
but couldn't find enough information to do it at the time mainly because I don't now much about
X windows and you have to sign NDAs to get hold of the information you need to program the
cards directly.

- Charles

zg3409
Posts: 32
Joined: Wed Mar 16, 2011 10:05 am

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

Post by zg3409 » Thu Mar 17, 2011 11:54 am

Hi Charles,

I would like to see a DVB-C (cable protocol) with MPEG4 (high definition) on a 2Mhz Bandwidth, for 70CM. I have not seen a trasmitter available that does this with this set-up. I have a TV (in Ireland) that can receive MPEG4 on DVB-C that covers 70CM without a need for a pre-amp nor up/down converter.

I have a thread with my views and questions here:

http://www.batc.org.uk/forum/viewtopic.php?f=15&t=887

If your software could transmit DVB-C then it might be an option for future transmissions. I am currently only considering DVB-C MPEG2 as I cannot find a MPEG4 transmitter and I can get hundreds of old DVB-C receivers with MPEG2 hardware.

Anyway if you are interested I can give you an MPEG2 DVB-C receiver

Your TV may already have a DVB-C (cable) tuner inside your TV. In my TV there is an option in the menu to change between Aerial and Cable and then there is an option for analogue or digital. If you pick cable, then digital it covers the 70CM band but using DVB-C only. It mentions DVB-C on the last page of the manual but the shop selling it has no mention of this feature on the website etc.

I am in no hurry for a MPEG4 DVB-C transmitter but if your interested I could send you a DVB-C tuner?

Daniel EI9FHB
Ireland

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

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

Post by G4GUO » Thu Mar 17, 2011 2:49 pm

Hello Daniel,

I currently have no plans to do DVB-C although my system being SDR based means
I can implement just about any TV system, it is just the time to do it.

As far as MPEG4 is concerned, I use the Hauppauge HD PVR a bit expensive but
it will work with both SD and HD.

I did see your post but as I didn't really have anything worthwhile to add I didn't
respond.

As far as 436 MHz DVB-S is concerned you can modify DirecTV converters using the
mods on Rob M0DTS website http://tinyurl.com/6k37ez8.
The converters can be picked up cheaply on eBay from the States, you still need a preamp
in front of them though. I have modified 2 of them so far, it takes about 30 mins to do.

I am currently looking at 10 GHz Digital ATV using old LNB parts.

- Charles G4GUO

zg3409
Posts: 32
Joined: Wed Mar 16, 2011 10:05 am

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

Post by zg3409 » Fri Mar 18, 2011 11:01 am

>I currently have no plans to do DVB-C although my system being SDR based means
>I can implement just about any TV system, it is just the time to do it.

No panic. It might be of interest in a few years for me. MPEG2 is OK for now.

>As far as 436 MHz DVB-S is concerned you can modify DirecTV converters using the
>mods on Rob M0DTS

Yes. I have seen that. It's a good option I considered it and it's still a good option.

>I am currently looking at 10 GHz Digital ATV using old LNB parts.

If you need a ready modified one, I can send you one. Normally we all try to use the same make & model as it makes modifying them easier. So let me know if you are stuck. Another problem is normally we don't know the exact down conversion frequency which is OK for analogue but could be harder for digital. It makes the read-out difficult to understand however once you know it, you can usually setup custom LNB settings in the software to make the readout understandable.

You have done a great service to Amateur TV so far with your work. I am reading with interest your blog so keep it up!

Dan EI9FHB

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

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

Post by G4GUO » Fri Mar 18, 2011 11:48 am

Hello Dan,

My Samsung TV can cope with both MPEG2 and MPEG4 I just have to tell it what it is
getting in the SI tables.

As far as 10 GHz is concerned I plan to use my PLL locked YIG @ 9 GHz to generate the
LO on both TX and RX (another eBay purchase). There is a picture of my YIG setup in the blog
(March 2010).

I have ordered some scrap LNB's from R.F Electronica http://tinyurl.com/6bvz4t9
plus a couple of Hittite 12 GHz mixers (for tx). The real problem is the 10 GHz BPFs.
I will have to see how much I can pull the satellite BPFs down using some dielectric material.
I only noticed that R.F Electronica sell Alumina (Er=10) sheet after I paid for my order (duh).

As you say the cheap receivers will be a problem, I have a spectrum analyser so I should
be able to 'calibrate' them before the punters get them.

Fine on the Blog, yes I get quite a few hits on that, I noticed after I posted about the 1.3 GHz
antennas on eBay there was a sudden surge in people buying them! I have not posted much recently
as I have not had too much time due to other commitments. However with the warmer weather
I should be spending more time in my rather cold workshop! I would like to get the FPGA based
testcard sorted out next.

I say testcard but with the 3 channel high speed 10 bit DAC on it, it will be possible to do a lot more
than just generate testcards.

- Charles G4GUO

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

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

Post by G4GUO » Fri Aug 31, 2012 9:37 am

Finally I have found a cheap way to receive my experimental 23 cms DVB-T transmissions.
Using a Newsky DVB-T dongle with RTL2832U / E4000 chipset (same as budget SDRs) and
it's BlazeHDTV 6.0 bundled Windows software.

The transmission parameters were
DVB-T 2K mode, 7 MHz channel, guard 1/16, FEC 3/4, QPSK, Video MPEG2 @ 5.8 mbits/s.
Power 2 watts, freq 1.3 GHz.

I have only tested MPEG2 SD at the moment but I know my code produces valid H.264
HD 1080i so that should work as well.

It was a bit tricky to get it to scan 23 cms but it can be done and it works, I am happy
and all for the princely sum of £12.90. Just noticed the guy I bought the dongle from
has upped the price to £16.90 (that is a shame).

When I am feeling enthusiastic I might try it with a DATV-Express board.

Update: I have tested it with 1080i HDTV and all is well. My Atom P.C struggles to decode
HD but it is a pretty slow machine.

- Charles G4GUO
Last edited by G4GUO on Sat Sep 01, 2012 11:56 am, edited 1 time in total.

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