HFU HF Underground

General Category => General Radio Discussion => Topic started by: Capt. Kidd on March 08, 2018, 2354 UTC

Title: Digital pirate tv transmitter
Post by: Capt. Kidd on March 08, 2018, 2354 UTC
This wil almost definitely demonstrate how little I know about digital tv but is it at all possible to build a digital tv pirate transmitter?
Title: Re: Digital pirate tv transmitter
Post by: TheRelayStation on March 09, 2018, 0324 UTC
yes but the distance wont be anything like analog.
many moons ago, i built an analog audio/video transmitter for channel 3 (unused at the time) using an extensively modified and tuned "3/4 modulator" from a VCR, two home made low-pass filters, two home made amplifiers and two home made vertical 1/4 wave antennas, each one for video and audio.
only operating at 1 watt for both video and audio, the distance was about 1000 feet on a portable TV but im sure the homes with roof antennas pointing in my direction (towards the TV stations) received the signal from much further away.
this was before cable tv was fully established around town when people were still using horizontal directional VHF antennas on their roofs.
can you imagine me walking down my street with a tiny portable B/W TV testing the signal distance ? - the neighbors thought i was very strange as i once observed a neighbor talking about how strange i was over their 46Mhz cordless phone :D
Title: Re: Digital pirate tv transmitter
Post by: SevenTrees' on March 09, 2018, 0336 UTC
Yes, but why would you want to?
https://www.youtube.com/watch?v=dKnwhokvgxE
Title: Re: Digital pirate tv transmitter
Post by: JimIO on March 09, 2018, 0432 UTC
Two words: cost prohibitive. Analog and digital transmitters are basically the same except for the modulator. Try finding an ATSC 8VSB modulator for less than $1000.
And if you could do it nobody would see you unless they happened to do a new channel scan while you were transmitting.
Title: Re: Digital pirate tv transmitter
Post by: redhat on March 09, 2018, 1606 UTC
ATSC modulators are very expensive, but most cable ready tv's made now support QUAM modulation, which is cheaper and more readily available in the cable industry.

I had a similar conversation back in the analog days with one of my mentors.  He seemed to think that 10W peak visual would be enough to cover a good chunk of a small town.  The reason; rooftop antennas.  We also had a low power station in town run by some looney guy who later started the fox affiliate.  I think he was running a lowband channel 2 with about 30 watts near downtown.  His antenna was 4 scala crossed horizontal folded dipole arrays.  At a building half a mile away where I worked we could see it, a little snowy though.

As an aside, the DATV people are using DVB-T modulation and equipment is relatively cheap but not compatible with US TV's.

+-RH
Title: Re: Digital pirate tv transmitter
Post by: fpeconsultant on March 09, 2018, 1616 UTC
Yes, but why would you want to?
https://www.youtube.com/watch?v=dKnwhokvgxE
Hah!!  Very nice - living in Chicago, I remember it well.
Title: Re: Digital pirate tv transmitter
Post by: Capt. Kidd on March 10, 2018, 0212 UTC
Two words: cost prohibitive. Analog and digital transmitters are basically the same except for the modulator. Try finding an ATSC 8VSB modulator for less than $1000.
And if you could do it nobody would see you unless they happened to do a new channel scan while you were transmitting.
So in theory all Id really need is an ATSC modulator, an amp which I could ether build or get as a kit from Free Fadio Berkeley and an antenna?
Title: Re: Digital pirate tv transmitter
Post by: redhat on March 10, 2018, 0719 UTC
Any of the digital waveforms are very sensitive to distortion, and a highly linear amplifier would be needed to get the modulator output up to a useful level.  This is not a trivial task, and one of Dunnifer's wonders won't do it.

+-RH
Title: Re: Digital pirate tv transmitter
Post by: JimIO on March 10, 2018, 1753 UTC
Build an analog transmitter first, then you could switch to digital later. And don't bother going above channel 36. I wanted to try using an old VCR to try to rebroadcast a OTA digital channel but I totally lost interest in TV. The few things I watch now are available by Torrent.