G’day guys and gals,
I’m wondering if it’s possible to feed a video signal directly into a TV antenna so that a receiver will pick it up on all channels. Cheers!
-R
In a word: No.
In a few words: the receiver is expecting to see the video signal modulating a carrier at the frequency the tuner is set to. This modulation is not a simple transformation, and lack of carrier signal at exactly the right frequency is interpreted as zero signal. One point of the receiver’s design is to ignore any other signal than the designated carrier, (including no carrier at all). Modulating a whole set of carriers, each at the individual carrier frequencies of all the possible channels, is theoretically possible, but building such a device would not be trivial, and I doubt one has ever been made.
Your OP is far from informative if you want a good answer.
Back in the day … if by “video signal” you meant RCA A/V cables (yellow video, red/white audio) and TV antenna/receiver you meant a coax/twin lead to an NTSC device, then you got yourself an RF modulator. A/V in, channel 3 or 4 out. Easy.
But with the switch to digital/HD TV, it’s not so easy. What is your video signal on? HDMI? DVI? What is your receiver cable of getting? NTSC (analog) ATSC (digital), etc.?
If you want to broadcast a signal to a remote TV (no wires), then you are a TV broadcaster and the FCC has rules about that. (You can do weak signals, but if you could find something prebuilt, you will not be happy.)
And the “on all channels” part makes no sense at all.
Please start over and make a new post that contains a lot more info and clarity.
describe what you want to do. there may be ways to achieve your goals beside what you might be thinking of doing.
Thanks for the replies guys. Some more info:
By video signal I mean any description of output coming from the laptop, and through a wireless system to a receiver, which will output RCA.
By all channels, I mean that the video feed from the laptop, feeds into the digital antenna socket, and any TV that receives from that socket, will see the same feed regardless of what channel they try to tune to.
I want to broadcast from the laptop over a 2.4GHz/900MHz wireless video system, and then that feeds directly to the antenna. So what I need, is a unit that goes between the 2.4/900 Receiver and where the antenna normally plugs in.
Hope that helps.
Fortunately, the FCC does not have jurisdiction over the entire planet, which means the OP might not need to worry about them. (Unfortunately, even in that case he probably needs to worry about some local equivalent…)
But is it really true that the FCC cares about broadcasting TV signals, even if it’s a weak signal? At least in Europe it’s possible to buy portable radios capable of broadcasting on any of the standard FM frequencies. They’re intended to be used to interface portable music players with car stereos that lack a cable input, and their signal has a range of only a few metres. If the OP uses a signal just strong enough to reach a television in his own home (and no further), then the local broadcasting regulations might not apply to him.
This is the sticking point. This is a non-trivial requirement, one that is not met without custom electronics that will not be cheap.
Essentially what would be required is a TV transmitter - that would output every possible channel (and sub-channels - dozens in all). When connected directly to the antenna inputs, this is called a ‘modulator’. It converts the video output of your PC to a radio frequency signal that is fed directly into your TV rather than a broadcast tower.
Prior to the digital conversion, these were available to connect video games to NTSC TVs without ‘video’ level inputs. They were not too expensive, but they only output channel 3 or 4 - not all. I don’t know if such things exist in the ATSC (digital TV) world. Try google for ATSC MODULATOR.
tv sets still can use NTSC RF in the USA.
It’s possible to buy them here, too.
in the USA they care about all radio signals.
By the way, why were 3 and 4 chosen, of all the channels available? Why not 2 and 3?
(I understand the reasons for providing a choice of two output channels, and for having them adjacent. It’s the particular choice of those channels that is mysterious to me.)
Just a guess, but they are lower frequencies (cheaper components) and 2 was a very common frequency in many markets, leaving 3 open. If 3 was taken, 4 was open since the FCC avoided adjacent broadcast channels.
2 was first on the dial. likely many more on 2 than 4.
2 is the first channel, so there’s more likely to be a television station there. Many people didn’t have a dedicated television for their computer or video game console; they’d sometimes want to use the console and sometimes watch TV. So by making the RF modulator default to a channel less likely to be assigned to a television station, you reduce the chance that the user is going to have to turn it off whenever he wants to switch from playing video games to watching TV. That is, instead of changing the channel on the TV and switching off the RF modulator (which might involve inconveniently reaching or crawling behind the set), all he has to do is change the channel on the TV. I suppose this might have been important if you were, say, routinely downloading large files from a BBS and wanted to switch to the TV while you waited.
Because 3 and 4 were adjacent, the possibility of interference was great, so the FCC never assigned both in the same markets. Therefore, the designer of compatible hookup equipment could be pretty sure one or the other was unused no matter where the location.
The original analog channel allocation scheme did not have all channels from 2…13 equidistant, although they were sequential. The radio FM band is smack in the middle (I forget the relevant numbers, but I’m sure someone will be along shortly to tell us).
server screwed up, duplicate post
just above 6 in the USA
The FCC can pry my Mr. Microphone out of my cold non-modulating hands!
Right. I was already aware of that. But then the same thing was true of most of the other pairs of adjacent VHF channels. (One exception: there’s a big frequency divide between channels 6 & 7, so that particular pair would have been a bad choice.) Why not pick 12 & 13, for example?
The reasons seem (so far) to be: (A) the lower the frequency band, the lower your modulator’s component costs — so ideally you’d grab 2 & 3 — however (B) channel 2 was occupied already in so many viewing areas, you might as well write it off and move on to 3 & 4.