Re: communications rates was Re: Differential voltage probes 3

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <teslalist-at-qwest-dot-net>" <davep-at-quik-dot-com>

(We are getting a bit away from Tesla, or HV....)

>>>Terry, I predict that just as we now have audio TC transmission we will
>>>have future video TC transmission with this new found wide 
>>>bandwidth.  It only takes 6-8 Mhz bandwidth for video.

>  > Sorry, but transmitting 6 MHz bandwidth on a carrier of a

>>few hundred KHz is forbidden by communications theory.
         Sort of.

         Shannon referred to _binary_ (on off) keying,
         or two tone tone signalling.  If multi level,
         either analog, or discrete steps be employed,
         more BW can be fit in.



>Not true...

         Sort of.


>- Communications theory (if you're referring to the Shannon law) only
>provides a limit on the amount of information you can get through a 
>channel, and doesn't constrain the bandwidth required for the

>information, other than setting a minimum Signal to Noise ratio.
>- Transmitted bandwidth doesn't necessarily follow the bandwidth of the
>modulating signal.  Take FM broadcast band, modulation bandwidth is on the
>order of 20 kHz, and the signal is >100 kHz wide.

         Design choice.  FM for eg 'police radio' is 15 KHz wide,
         for 10 KHz (roughly) audio.  The wider channel
         spacing in 'broadcast FM' allows for more fidelity.

>  Or, AM broadcast, where the modulation is some 5-8 kHz, and the

>transmitted signal is 15 kHz wide (being DSB).


>- Baseband video (like comes out of the VCR) is 6 MHz wide, at a

>carrier frequency of ZERO.
         Basebaand video, by deninition HAS NO carrier.

         When broadcast (or otherwise on a carrier) it is
         a sort of single side band, with a 6 MHz BW....


>One can certainly transmit very high rate digital signals in a fairly 
>narrow bandwidth, IF you have enough power.  HDTV is some

>20Mbps in a 6 MHz wide channel.  56k modems are doing 56 kbps

>in a 3 kHz channel.
         by using multi level encoding.  The Shannon

         bit/Hz criteria ASSUMES BINARY keying.

         best
         dwp