Broad casting TV

[drkidd22]

So I was thinking about how it's really done. This might not be right place to post it but if it's not please move to correct location.

Back home I live on a town about 10-15miles diameter lets say.
If I wanted to broadcast TV over the air say on channel 12, what kind of equipment will I need?
Forget about FCC laws and stuff as I'm just trying to do some research and figure out if it would be something worth me doing.

 

[edeca]

Something like **broken link removed** or How Television Broadcasting Works would be a good place to start. It's a complex subject from start to finish, you'd be better posting individual questions such as "how is the image modulated onto the right frequency" or similar.

 

[crutschow]

Even if you broadcast on an unused channel, it can splatter over into the used channels and raise the ire of people in your town and the FTC. That's why in analog TV broadcasting, the stations always have an unused station in between, to minimize crosstalk between channels. Channels 4 and 5 are exception to this rule, but those two have a large frequency gap between them so there is no possibility of a problem.

 

[stevez]

Quite a few licensed radio amateurs broadcast TV - within the limits allowed by FCC regulations. Worth noting is that some use HF (shortwave) to broadcast low resolution (a relative term) over great distances. Some cities or metro areas have quite the number of radio amateurs involved in this mode on VHF and UHF frequencies.

 

[Nigel Goodwin]

Quite a few licensed radio amateurs broadcast TV - within the limits allowed by FCC regulations. Worth noting is that some use HF (shortwave) to broadcast low resolution (a relative term) over great distances.

Hardly a 'relative' term, they use SSTV (Slow Scan) on HF bands, due to bandwidth limitations - effectively a picture every 30 seconds or so.

It's not until 70cm's that you have the bandwidth available for normal broadcast standard TV.

 

[Hero999]

Why did they go for 60Hz in the end?

24Hz is good enough for most purposes, I'd prefer a higher resolution with less frames per second.

 

[PCBWING]

Transmitter? there may be side effect.

 

[Gary B]

Some things to keep in mind:
First, HDTV has caused all of the traditional VHF channels to be abandoned by TV. Other services are moving in like a land rush.
Second, Are you attempting to talk analog color, analog B&W, the new digital HDTV standard or one of the other digital standards used around the world?
For the most part, if you are out by yourself and keep your input power to the final stage below 100mw, you can get by under FCC rules part 15. That should let you put the transmitter in the barn and pick it up in the house.

 

[Gary B]

Why did they go for 60Hz in the end?

24Hz is good enough for most purposes, I'd prefer a higher resolution with less frames per second.

It was actually 30 frames per second because of the interlace. The frequency was selected to minimize power line distortions in the picture caused by powering the vacuum tube heaters off an under-filtered power supply.

 

[Sceadwian]

Hero for static image fidelity resolution is truly king; far too often overlooked is framerate for video fidelity. Personally I don't think 30 or 60 is even close to enough for motion action, I would like to see 100-200+ frame rates, but the bandwidth goes up so fast and most sheople are happy with 30 frames per second. Most people quote the 24hz as being 'good enough' but it's not, it's the accepted minimum frame rate that can describe minimal motion video for typical human motion. The human eye can see hundreds of times faster than that though.

There's currently a post a user made on here because they were able to notice the flicker in a flash on their cell phone, which probably was at a few thousand hertz. If we can notice that, what are we really missing as far as motion fidelity goes? Look out a window watch something at a distance and have a bird cross your field of view at a close range. We can't analyze frame for frame, but we CAN see time based visual elements of hundreds or thousands of hertz.

 

[drkidd22]

sounds like it could kinda challenging to accomplish what I want to do.
As far as equipment needed to transmit a tv signal what would it be needed?

will something like the Cisco IP/TV 3420 Broadcast Server do it?
or will I need something like **broken link removed**

 

[Sceadwian]

Considering without a license you can't legally broadcast it would be in the best interest of everyone not to help you =) You can't forget about FCC and laws 'and stuff'
Analog TV broadcasting is trying to be supplanted by digital TV broadcasting on the same frequencies for a VERY good reason, it is incredibly wasteful of bandwidth. If you chose to do your project regardless of warning or concern for the general RF world... It's just not good. It shows a lack of concern for what you might do to those around you, rude by anyone's perception. You have one goal and one goal only, what you want to do, you've shown not one single iota of concern for what you might be doing to other people.

 

[mbarazeen]

one of the follwing will cover the range of your town

**broken link removed**

**broken link removed**

 

[Hero999]

There's currently a post a user made on here because they were able to notice the flicker in a flash on their cell phone, which probably was at a few thousand hertz. If we can notice that, what are we really missing as far as motion fidelity goes? Look out a window watch something at a distance and have a bird cross your field of view at a close range. We can't analyze frame for frame, but we CAN see time based visual elements of hundreds or thousands of hertz.

I think there's a huge difference between the frame rate required for motion and the frequency required for a light to appear continuously on.

I know for a fact that a lamp flashing 24Hz would be horrible, the flicker would be really obvious but when I watch a film running at that frequency I don't think it appears jerky, maybe a higher frame rate would be better but I think I'd notice a higher resolution more.

The reason for this is because when a light flickers there's a huge difference between the on and off states, much more than from one frame to the next on a film, most of the time the light intensity is similar, it's just things have moved around a bit.

 

[Nigel Goodwin]

one of the follwing will cover the range of your town

And of the local jail as well

 

[mbarazeen]

And of the local jail as well

its his problem, he mentioned not to bother about it. who knows how strong are the local authorities in his area... his question was what equipment he can use.

 

[Nigel Goodwin]

its his problem, he mentioned not to bother about it. who knows how strong are the local authorities in his area... his question was what equipment he can use.

It would be remiss of us not to make sure he knows he would be commiting an offence, and one which is easily caught - it's not difficult to find the location of a transmitter.

 

[Sceadwian]

Especially if the transmitter is designed to cover 15 miles.

 

[Nigel Goodwin]

Especially if the transmitter is designed to cover 15 miles.

Certainly so, to give 15 miles of decent picture quality, you're talking kilowatts, not watts.

 

[Hero999]

Then of course there are the safety implications of high powered RF devices, it doesn't take much power to damage sensitive tissues in the eyes, brain and gonads.