Re: Radio waves...

[SCIAMANDA@edinboro.edu]

David Bowman wrote:
> I'm quite surprised that a telephone line could have a S/N remotely as high
> 56 db.  This seems to be a dynamic range of better than 18 bits.  This seems
> to be at least CD quality sound here.  When I use the phone there often seems
> to be significant background noise and have a hard time believing that there
> can be a S/N anywhere near that high.  I also didn't know that the telephone
> channel bandwidth was as high as 3000 Hz.  The voices I hear over the phone
> usually seem to sound more distorted than I would expect from a 3000 Hz
> bandwidth.
> David Bowman

I think you made an oops!  Check my math for oops:

56db = 20*Log_10(V2/V1)

V2/V1 = 10^(56/20

V2/V1 = 631 which fits easily into 9 bits.

As regards the bandwidth of a standard telephone line,  I have seen 
both the range (300-3300)Hz and the range (300-3400)Hz quoted in 
the literature.  If crucial, I'll dig out a reference. Your figures 
may represent an older standard.

(Also, I may put a scope on my phone line and see what kind of 
S/N ratio I can measure.) - Later

Bob Sciamanda           sciamanda@edinboro.edu
Dept of Physics
Edinboro Univ of PA     http://www.edinboro.edu/~sciamanda/home.html