🚀 go-pugleaf

In article <1480@unccvax.UUCP> dya@unccvax.UUCP (York David Anthony @ WKTD, Wilmington, NC) writes:
>In article <1968@hp-sdd.hp.com>, robert@hp-sdd.hp.com (Robert Navarro) writes:
>	No, no, no, no, no, no, no.
>
>	The baseband signal is **not** limited to 5 kHz.  Where do people
>get this stuff (and we AM broadcasters wonder why the band is deteriorating).
>There are AM **receivers** which are bandlimited to 5 kHz; but the fidelity
>limit (twice the bandwidth, by your own emissions) generally is unlimited
>within the service area.
     Maybe they have changed the FCC standards lately, I'm not sure. But 
the according to everyone I've talked to at work and a professor at San
Diego State in communication electronics the bandwith for commercial AM 
is 10KHZ. If a broadcaster is within this limit, then their is only 5khz
worth of signal information in the receieved 10khz signal since the
two sidebands are mirror image duplicates of each other in commercial
AM. Also "Reference Data for Radio Engineers", Howard Sams Inc. 1979 states
on page 30-1, "Standard-broadcast stations are licensec for operation
on channels spaced by 10 kilohertz and occpying the band from 535 to 1605
kilohertz." Admittedly, this does not limit the bandwidth of a station 
to 10khz (other FCC regulations may though, but I don't have a copy
of the regulations on hand.) it only means that channels are assigned
in 10khz increments. Now, that means that to avoid interference stations
should only have a bandwith of 10khz. A station may broadcast a signal 
with bandwidth greater than 10khz, but they better talk to the FCC and make
sure there are no nearby stations or there's going to be some major
interference. 
    I'm really not sure what you mean by "the fidelity limit generally is 
unlimited within the service area." But since the Random House College 
Dictionary defines fidelity as the ability to receive electronic signals
accurately, I would say that either your not using AM as your modulation
scheme or you have unlimited carrier power within your service area. (Maybe
you also use AM radio to power your house like in Tesla's power 
distrubution scheme.)
 
>	Nice AM broadcasters have installed NRSC-1, the national voluntary
>standard which mandates a 10 kHz baseband signal with 75 uS preempasis.
>
10khz baseband doesn't sound bad, but it's not quite high 
fidelity.
>
>	Do you own an AM stereo receiver? Do you live in a market 
>which has radio stations using the Kahn ISB system? Do you own an
>NRSC-1 compliant receiver (with 10 kc bandwidth and deemphasis)?
    I'm really not all that interested in owning AM stereo as long as
it is a system that is built to be backward compatible with mono AM. To make
a really good system you'd have to trash the current AM setup and start 
over again (probably at a higher frequency range and using SSB)

>
>	If you had owned appropriate AM receivers, you would know
>why the Kahn ISB system is not noisier in stereo. 
I don't own the system nor do I know it's setup -- so no comment. 

>	Say **what**?
>        FM is not inherently a less noisy modulation scheme than
>AM. What do you think the FM stereo subcarrier is...suppressed
>carrier, double sideband AM!
>
    The fact that the FM subcarrier L-R signal is modulated to 38 khz 
using DSB-SC does not greatly effect the transmitted FM signal's noise
immunity. Most of the noise corrupting an RF signal currupts it's amplitude
the frequency is much harder to corrupt. In FM systems the first thing
they do is hard limit the signal, therby eliminating all AM varations
in signal and hence most of the noise associated with AM. Only after 
the signal is recieved in FM and demodulated into a compostite baseband
signal with the L-R channel at 38khz is the the L-R channel demodulated. 
But since this signal is derived from a signal received and demodulated
in FM it will not suffer from the noise effects that a normal AM signal would
suffer from. 


There's a lot math that I went through years ago to show that FM is better
that AM. If I have time , maybe I'll look it up later at post it. Till 
then read a good book on communication systems to see more on why FM 
is better than AM.

Robert Navarro
Hewlett Packard San Diego Division.

-- 
Robert Navarro