frequency question

[donkey]

hey all. just a quick q about frequencies.
is it true the higher the frequency the more data it can send?
I just noticed that 433mhz are rarely used for streaming video but 2.4ghz is. so I was wondering... if anyone can shed light on the subject please do so

 

[duke37]

It is not so much the frequency as the bandwidth. A TV channel needs a bandwidth of 4 or 5MHz so if you used a low frequency, this would take the whole of long wave, medium wave and a considerable amount of short wave.

At the very high frequencies there is more room and it is easier to make a signal in which the bandwidth is a small proportion of the frequency.

 

[MattyMatt]

Duke is correct, bandwidth on the higher frequencies is greater. The other thing you want to consider is the nature of the stream. Will it be analog or digital?

Analog broadcast TV here in the US (which is pretty much gone), took 6-12 mhz per channel. Digital Broadcast now take 3-4mhz (pretty sure on this number but not 100%). So in all practical uses, with digital, not only can the broadcaster stuff a better looking picture in the same space, but they can effectively put more "channels" into the same space (for example, 24.1, 24.2, 24.3, 24.4 which is local PBS here are 4 "sub-channels" of 24).

What kind of a project do you have in mind? or was it just a random question ?

 

[davenn]

Duke is correct, bandwidth on the higher frequencies is greater.

careful you are almost making the same mistake a higher freq doesnt have a greater bandwidth. There is just more spectrum to play with.

Analog broadcast TV here in the US (which is pretty much gone), took 6-12 mhz per channel. Digital Broadcast now take 3-4mhz (pretty sure on this number but not 100%). So in all practical uses, with digital, not only can the broadcaster stuff a better looking picture in the same space, but they can effectively put more "channels" into the same space (for example, 24.1, 24.2, 24.3, 24.4 which is local PBS here are 4 "sub-channels" of 24).

a standard analog channel with sound is ~ 6MHz ( 6 to 7MHz)
Standard Definition digital is as you say ~ 3-4 MHz but a HD digital signal is ~ 20MHz but with some nice MPEG-2 and encoding and other tricks they can get that down to ~ 6MHz
MPEG-2 isnt the most brilliant encoding method, its pretty lossy. But for the most part its still much better than an analog signal.

The cool thing with doing digital tramnsmissions tho, is that in the same 6MHz or so channel allocations you can, as you said, cram in a more channels. This is done by the different modulation methods and different multiplexing methods, things that cant be done with an analog signal.

Dave