A Low Cost Analog and Digital TV (DVB-T) Modulator

Capt'n Midnight

http://fabrice.bellard.free.fr/dvbt/

With a PC running Linux and a recent VGA card, you can emit a real digital TV signal in the VHF band to your DVB-T set-top box.

DVB-T emitters are usually very expensive professional devices. Now with a standard PC you can broadcast real DVB-T channels !

Examples to transmit PAL or SECAM analog signals directly to your TV are also presented.

What do you need ?

* A good knowledge of X Window and Linux and basic knowledge in electronics.
* A DVB-T set-top box able to receive VHF signals with a bandwidth of 8 MHz (unfortunately most decoders sold in UK only receive UHF signals). You can use French DVB-T receivers which accept VHF and UHF RF signals.
* A PC with a recent VGA card able to display in resolutions up to 4096x2048 with 8 bit per pixel with a pixel clock of exactly 76.5 MHz. ATI Radeon 9200SE are reported to work (their PLL can generate every frequency which is a multiple of 2.25 MHz up to 400 MHz). Other VGA cards may work too. If your card cannot generate a 76.5 MHz pixel clock, I can provide alternate images to do some testing.
* A cable connecting the VGA output to the set-top box RF input. It is possible to use antennas, but since the transmit power is very low, it is better to begin with a cable connection.

15 pin VGA connector 9.5mm RF connector

---

---

1 (red signal) <

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> RF signal (central pin)
6 (red ground) <

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> GND

watty

Extremely limited.

But a very good trick!

A better solution is a Bench Tester for DVB box. About $3000 new and less second hand.

It has facilities for analog video in, MPEG stream in, data in.

Typically the output is 2 TV channels (one is external video and 2nd is an internally generated test card), a data stream and several audio channels from internal test signals and external analog or data stream.

Of course QPSK (effectivly QAM 4 with a single carrier) is much easier than COFDM with 64 QAM! But then you need a Satellite receiver and not a DTT revceiver!

Sponge Bob

watty wrote:

A better solution is a Bench Tester for DVB box. About $3000 new and less second hand.

At that price it'd wanna be Watty

Of course QPSK (effectivly QAM 4 with a single carrier) is much easier than COFDM with 64 QAM! But then you need a Satellite receiver and not a DTT receiver!

Were one already in posession of a laptop with (analogue) TV Out then a mere €89 will upgrade it to do what the Cap'n seems to want .

watty

yes and DVb-t PCI cards or entire box for TV are about same price (for Receive).

If I have nothing to do I may try the "modulator" approach. But since it entierly ties up a fairly high end PC and better graphics card that most here, it isn't cheap. Near 600 Euro worth of kit if you went out and bought the bits.

This
http://www.uniquesys.com/products/broadcast/dvb/dvb-t-h-modulator-pci.html
or
http://www.uniquesys.com/products/broadcast/dvb/dvb-t-h-modulator-2000.html
(requires upconvertor, which is not expensive).

Would be good for the project I plan for late summer.

These people look more interesting:
http://www.computermodules.com/broadcast/DVB-ASI-SMPTE310M-PCI.shtml#dvb

lawhec

The main problem with this approach is that most DTT STBs in the UK don't cover the VHF band, UHF only. I believe that the Thomson 2300 is one exception.

Of course QPSK (effectivly QAM 4 with a single carrier) is much easier than COFDM with 64 QAM! But then you need a Satellite receiver and not a DTT revceiver!

OTOH, I think the same STBs can cope with QPSK, it's part of the DVB-T standard.

Sponge Bob

my link above will do

174-865 MHz VHF/UHF
Channel Sizes 6 MHz, 7 MHz, 8 MHz
Sensitivity -75 dBm
Modulations 16 QAM, 64 QAM, QPSK

watty

One of those would be nice on my laptop if it had 100Hz refresh.