digital TV modulator

[joseph2k]

how much could you do in the fpga ?
just the modulation to feed into a uhf freq shifter ?
perhaps usb interface that would be usefull,
or maybe do the mp2 encoding too,
or even analogue video in too, say composite or whatever,
although theres probably a chip that would do the a/d nicely,
or hdmi ...

if it was a fpga and a uhf mixer that wouldnt be so hard to do,
although software always takes longer than you want,
and those fpga are awfully tetchy about being soldered deadbug style,
i dont know how big those kits are.

I would imagine just trying to interpret the standards would be hard
enough judginbg by the way many such things are becoming more and more
complex.

and would anyone else realy be interested ?
might be cool if there was some shared effort.
no ones come up with a commercial offering yet so I assume there isnt one,
save for broadcats studios.


Colin =^.^=

I figure that 1 or 3 a-to-d converters for the analog input, 2 d-to-a
converters for the baseband / if (40 MHz or 70 MHz) output, a uC to load
the FPGA, a FLASH chip to store the programs, and the modulator out of a
standard tv converter. (yes the primary difference is the baseband signal
content).

 

[AZ Nomad]

Hi,

Im using my vcr just as a UHF modulator (analogue) but analogue is becoming
obsolete,
and im thinking of doing away with the vcr, and getting a tv with digital tv
tuner but no analogue,
is there an equivalent modulator for digital TV ?

Get a digital tv with VGA, DVI, or HDMI inputs. They're very common.

 

[colin]

Get a digital tv with VGA, DVI, or HDMI inputs. They're very common.

yes I think they all have those now,
but I like the idea of being able to use the tv's internal digital tuner to
send the video via a single coax or even through the air a short distance,
and without having an external box, just use the internal dvb-t receiver.

so i can have a tv virtually anywhere without a dozen rg58 cables going to
it.

Colin =^.^=

 

[colin]

I figure that 1 or 3 a-to-d converters for the analog input, 2 d-to-a
converters for the baseband / if (40 MHz or 70 MHz) output, a uC to load
the FPGA, a FLASH chip to store the programs, and the modulator out of a
standard tv converter. (yes the primary difference is the baseband signal
content).

well that wouldnt be too difficult to put together,
ive got an old video card with vivo that must have the a to d on there
somewhere,
the uhf modulator is childs play, I made one when I was a young teenager
with a bfy90,
as part of a TV pattern generator using just basic logic gates.
ive got a few spare PICs and an old bios flash chip or 2.

I had a quick look on wikipedia for DVB etc and it talked about many of the
digital baseband encoders using QAM
for cable tv as well, so theres probably a chip that would to that for you.
maybe AMD.

I bet you could fit it all into a pocket sized box.

ofc this would become easier if it was part of a PCI card exept the PCI
interface is probably just as complicated itself unless youve done it
before. part of the signal would be to transfer digitaly stored movies, the
other would be from the cable tv box, although the cable tv itself receives
digital signals anyway .... and my cable tv box has a uhf output anyway,
just a real shame its not DVB, would be so nice if they decided to do that
....

However I cant imagine for a minute I would end up doing all this,
my original idea was to use something commercially availbale.

but its amasing what people do create, such as home made spectrum analysers
etc etc.

Colin =^.^=

 

[colin]

I figure that 1 or 3 a-to-d converters for the analog input, 2 d-to-a
converters for the baseband / if (40 MHz or 70 MHz) output, a uC to load
the FPGA, a FLASH chip to store the programs, and the modulator out of a
standard tv converter. (yes the primary difference is the baseband signal
content).

wow ive been googling on and off for a few days now and this ive just come
accors this ...
http://fabrice.bellard.free.fr/dvbt/

it uses a standard vga card as a DAC and uses harmonics of this to generate
VHF signal directly to a DVB tuner, unfortunatly its not UHF, but hey its
close and may be room for upconverting, maybe simply selecting and
amplifying higher harmonics ?

I wonder if the video out capability could be used instead, thus alowing use
of the PC monitor as normal ...
or in that case a DAC conected to the parallel port ?
maybe just a small unix box, with hard disc to store movies ...

the software sounds complicated but has already been done.

Colin =^.^=

 

[colin]

In a few _years_? You can do that today as I've been watching HDTV
over cat 5 cable for over a year. You need an HD tuner and a home
network. The computers don't need to be rockets either but you will
need large drives as HDTV can use up to 8.7 gig/hour.

whats the HDTV broadcast standard status at now, are we likely to see HDTV
tuners inside the TV
or is DVB-t capable of this now anyway ? i was still a bit confused after
reading lots of stuff i found on wiki
it seems we have had BBC HD tv terestrial trial broadcasts here in the UK.

id realy like just to have a cable and a tv with no extra box so it is
possible to move it anywhere as easily as possible, with the posibility of
short range hop through the air. HDTV would be the ultimate, if the tuner
inside the TV was capable.

seems theres already software to use the ADC on a PC video card to generate
the baseband DVB-t signal.

Colin =^.^=

 

[joseph2k]

wow ive been googling on and off for a few days now and this ive just come
accors this ...
http://fabrice.bellard.free.fr/dvbt/

it uses a standard vga card as a DAC and uses harmonics of this to
generate VHF signal directly to a DVB tuner, unfortunatly its not UHF, but
hey its close and may be room for upconverting, maybe simply selecting and
amplifying higher harmonics ?

I wonder if the video out capability could be used instead, thus alowing
use of the PC monitor as normal ...
or in that case a DAC conected to the parallel port ?
maybe just a small unix box, with hard disc to store movies ...

the software sounds complicated but has already been done.

Colin =^.^=

Almost sounds like any cheap VHF to UHF converter will finish the job. Size
required to build one from transistors is about a pack of gum.

 

[Gary Tait]

whats the HDTV broadcast standard status at now, are we likely to see
HDTV tuners inside the TV
or is DVB-t capable of this now anyway ? i was still a bit confused
after reading lots of stuff i found on wiki
it seems we have had BBC HD tv terestrial trial broadcasts here in the
UK.

The DVB-T transmission system can carry HD. The question is can a DVB-
tuner tune the HD in a form your display can use.

id realy like just to have a cable and a tv with no extra box so it is
possible to move it anywhere as easily as possible, with the
posibility of short range hop through the air. HDTV would be the
ultimate, if the tuner inside the TV was capable.

seems theres already software to use the ADC on a PC video card to
generate the baseband DVB-t signal.

Colin =^.^=

You have 3 tasks to fulfile, maybe 4.

1: Digitise video and audio.

2: Compress the video and audio.

3: Mux and DVB-T modulate

4: Convert to RF frequency.

 

[Rüdiger Leibrandt]

Small Note:
You have a HF carrier - that signal is by frequency identical to the old
analog transmissions. It's carrier is identical even, 'cause some old TV's
still lock in on digital transmissions. The signal they carry, however,
varies muchly:Whilst the old analog standard contains a FM modulated
line-by-line-image plus, overlaid easiyl due to its lower frequency, the
audio, on a digital transmissions there is , like on a Modem, a digital
encoded Datastream. One Carrier can carry several valid MPG streams
actually, which in themselves are "just" normal MPG streams, typically 4
MBit per second.

I don't know of any currently reasonably priced homesolution to modulate a
digital datastream upon a HF carrier.

 

[Jan Panteltje]

On a sunny day (Tue, 19 Jun 2007 10:05:00 +0200) it happened
<[email protected]>:

Whilst the old analog standard contains a FM modulated

line-by-line-image

AM with one suppressed sideband actually, neg modulation, peak amplitude = sync = black
to make noise appear black and have sync before picture if signals are weak.

plus, overlaid easiyl due to its lower frequency, the audio.

Well actually 'intercarrier' but audio can also be seen as a separate
carrier (AM or FM) about 5.5Mhz higher (in Europe).
In fact for the old TV stereo where I am, there were 2 FM carriers, one modulated
with te sum (L+R) / 2 and and the other with the difference, so if you had a mono
receiver with one detector you'd at get both channels

on a digital transmissions there is , like on a Modem, a digital
encoded Datastream. One Carrier can carry several valid MPG streams
actually, which in themselves are "just" normal MPG streams, typically 4
MBit per second.

Modulation = QAM so just quadrature, maybe with 64 'stars'.
Where I am (Netherlands) it is QAM 64, with FEC 1/2, so lots of correction bits....
QAM 64, it is almost analog ;-)

I don't know of any currently reasonably priced homesolution to modulate a
digital datastream upon a HF carrier.

I have seen a FPGA solution on the web some years ago.

I just bought a USB DTV box, plugged it in the PC, and, if must be, can use VGA out....
And I can record:
ftp://panteltje.com/pub/dvb-t-nl.txt
Less then 30 Euro.
Of course I can also stream to the Internet, or just LAN via RJ45.

Solves OP problem... cheap coax from VGA.
And you still have your PC screen available.

 

[colin]

I have seen a FPGA solution on the web some years ago.

I just bought a USB DTV box, plugged it in the PC, and, if must be, can
use VGA out....
And I can record:
ftp://panteltje.com/pub/dvb-t-nl.txt
Less then 30 Euro.
Of course I can also stream to the Internet, or just LAN via RJ45.

Solves OP problem... cheap coax from VGA.
And you still have your PC screen available.

thats talking about receivers if im not mistaken, my problem,
or rather what I would like to do is to utilise the DVB receiver already
inside my TVs
in the same way as with the earlier tuners, as its digital it shouldnt
impare the quality.

I already have a cable tv box, so I get video into my pc from that if i need
it,
id just rather have less wires than I do now rather than add more to go to
my tv in the living room
and to also to tvs in other rooms.

I gues its just a question of price at the moment, as the only available
ones are industrial ones.
although that fpga solution sounds interesting if you can stil find where
you saw it.
using the DAC of a vga card as a IF qam modulator was interesting too,
although i think that was just done with individual pictures rather than
video.

Tvs without the old type tuner are perhaps upto $100 cheaper, so that would
not be a high price to pay for a modulator.

an other option is to use those microwave video senders, but that still adds
clutter at the tv.

Colin =^.^=

 

[Jan Panteltje]

thats talking about receivers if im not mistaken, my problem,
or rather what I would like to do is to utilise the DVB receiver already
inside my TVs
in the same way as with the earlier tuners, as its digital it shouldnt
impare the quality.

A 'digital tuner' in its simplest form (like I have for satellite for example) has an 8 bit
databus and some i2c control signals.

although that fpga solution sounds interesting if you can stil find where
you saw it.

Several places, just google 'fpga DVB-T modulator'
http://www.commsonic.com/products/dvb_t_mod.htm

using the DAC of a vga card as a IF qam modulator was interesting too,
although i think that was just done with individual pictures rather than
video.

Yes, and then you have no PC display

Tvs without the old type tuner are perhaps upto $100 cheaper, so that would
not be a high price to pay for a modulator.

an other option is to use those microwave video senders, but that still adds
clutter at the tv.

Analog is not nice, I tried some myself, too much interference, always needs tuning.
I have wired the house with Ethernet, connector in every room.
I have one switch, it is a star configuration.

But I have wireless too, mpeg2 transport stream via WiFi works very well here too.
In fact I converted a Linksys access point to a web server, added an SDcard, so
now I have all mp3s on it (no you cannot access those):
http://panteltje.com/panteltje/wap54g/index.html#wapserver
Log in with user 'guest' and password 'none' (without the quotes).
It may or may not work, just testing a new name server I wrote...
if you get 'address not resolved' try:
http://81.207.135.196/panteltje/wap54g/index.html#wapserver
The idea is (but speed is an issue) to put movies on it too (DivX likely).
The whole thing uses only 5 Watt, very green server.

The universal connector for today is RJ54 I think, analog is dead.