Archived posting to the Leica Users Group, 2000/11/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Jim- Remembering my communications days, and what I remember about Shannon's Theory is that the amount of information is related to the number of changes of state a carrier can make in a given time period- the frequency in other words. That is to say, if you have a state change- from zero to one as in a digital system per second, then you have a one Hertz signal. The higher the frequency, the greater the potential information carrying capacity. On old style systems, the higher the frequency, the greater the bandwidth needed. So a television signal required a 6Mhz bandwidth because that much spectrum was taken up by the sound and image signal. I think this idea has carried over even into the digital age where the information coding no longer actually depends on the ability of a line to carry a wide spectrum of frequencies. Dan - ----- Original Message ----- From: "Jim Brick" <jim_brick@agilent.com> To: <leica-users@mejac.palo-alto.ca.us> Sent: Wednesday, November 29, 2000 10:29 AM Subject: [Leica] Re: Bandwith > At 09:49 AM 11/29/00 +0200, you wrote: > >> > >>The reference is to the term Bandwidth. The context in which this is used is > >>wrong. > >> > >>Bandwidth has nothing to do with the length of a message. A message of 2 hour > >>length uses no more bandwidth, than a message of one second. > >> > >>Bandwidth has to do only with the actual speed a message is send. If a > message > >>is send with a speed of 300 baud, then the bandwidth is less than > >>if a speed of > >>1200 baud is used. > > > > Actually, in this RF & ether age, "Bandwidth" has taken on the meaning of > "VOLUME" which does not necessarily relate to actual moving speed, ie, 1200 > baud vs 2400 baud. Think of it like water in pipes. Pump up the pressure, > make the water go faster, you do indeed get greater bandwidth, that is, the > delivered volume is greater. Also, by making the pipe fatter, or adding > multiple pipes, yet keeping the same flow rate, the delivered volume is > greater. > > ISDN is made up of two 64KB data lines. Quite often only one is used. If > there is a backlog of data to be sent, the other line will kick in. The > data is still being sent at 64KB/sec but there is twice as much of it > getting through. More bandwidth. > > So in reality, long message use up bandwidth as they require volume. > > Jim >