"Bob in CT" wrote in message
news
On Fri, 06 Aug 2004 09:56:38 -0500, clifto wrote:

James Nipper wrote:
I can't see digital/non-digitial having anthing to do with it. TV
signals are RF, whether the modulation is digital or not.

However, not being an expert, I could be wrong.

I'm no expert on digital either, but I do recall a newspaper article a
while back, from the early days of digital in Chicago; people three
miles
from the transmitting antennas were having a great deal of trouble
getting
any usable signal. I get the distinct impression that digital needs a
MUCH
cleaner signal than analog.


There are people receiving signals at over 60 miles (both digital and
analog). See:

I agree; our experience with both analog and digital inspires this comment
which generally agrees with the "MUCH cleaner signal" requirement.
Without getting into too much detail of the different technologies to any
extent I offer this;
TV, especially digital has got 'better quality' over the years since it was
first introduced as simple black and white, non stereo etc.
So the signal now transmits more bits of information, colour, five channel
sound, program schedules, text of the voice and other information!
Also there is a basic difference in the nature of digital versus analog
signal modulation.
The simplest radio transmission of all was the dot/dash (morse Code). All
that was needed was to able to 'hear' the transmission going on and just a
little bit.. Even with severe noise; noise that perhaps could be stronger
than the radio signal itself, it was only necessary to detect the slight
change in order to be able to read the message! Very slow limited
information but could often be the best or method of last resort!
Next came AM (amplitude modulation) or analog, where the signal strength is
modulated up and down in time with speech music or picture. Again even with
noise as long as it is possible to 'hear' the variation it is usually
possible to read the signal. When TV was introduced analog was used; noise
due to a weak signal or otherwise can interfere with analog TV and may cause
everything from a hissing noise, slipping or rolling of a TV picture or
'snow' on the picture. But in many cases as long as the picture can
resynchronize itself fairly quickly the human eye and ear can tolerate the
slight interruption.
Airlines still use AM modulation for some frequencies because it is still
considered that there will be a better chance of hearing a weak or
interfered with emergency signal from a flying or downed aircraft!
FM, frequency modulation was introduced especially for the sound part of TV
and also for 'FM' stations. Better quality but using much more bandwidth and
it has gained a reputation for 'When it works well the quality is good; very
good, allowing stereo and other high quality sound transmission etc". FM
also used for many VHF police, taxi and military radios systems with the
channels packed much closer together than TV.
Finally digital, where the signal is sort of turned on and off many millions
of times per second, works very well and allows a lot of information to be
transmitted provided there is good bandwidth (bandwidth has to do with speed
of transmission available that's why you can't receive a TV programme over a
telephone dial up on the internet!). This provided the signal is not
interfered which means good clear signal from the digital transmitting TV
station or from a satellite. When all the digits are received the TV
receiver reconstructs the picture and sound etc. perfectly. However if
digits are lost or interfered (due to noise or weak signal or interference)
the receiver lacks the information to reconstruct the picture. We also have
digital satellite and it very frustrating when the screen breaks up into a
series of meaningless rectangles! Interference with the digital signal
sometimes makes loud noises on the sound! Heavy rain with a certain size of
rain drops causes more trouble with our received digital signal than does
snow!
Getting a clear signal path between you and various TV stations which may be
in different directions from your location is important. Also your TV
antenna has to cope with several different frequency channels; so most TV
antenna are a compromise!
The biggest current issue that is IMO worth mentioning to posters is
'interference'; it appears that the profusion of electrical devices we use
today, everything from a Christmas Tree light flasher, microwave oven, light
dimmer switches, our personal computers, hair dryers/shavers, blenders etc.
etc are not manufactured or regulated to standards by the FCC (or other
regulatory authorities in other countries) so they do emit interference or
radio energy, which they should not?
The most current of these is some trials of sending digital and internet
signals over the power lines; commonly called BPL. BPL trials in a number of
countries have been cut short because of interference with critical services
such as ambulance, police and aircraft to ground communications! The problem
with BPL being that the overhead wires are carrying not only the electrical
energy they were designed for, which doesn't radiate to any great extent.
But for these other radio/digital signals; the overhead wires are in effect
a very large and very extensive transmitting antenna!
So if you get 'interference' complain to your political representative for
proper regulatory enforcement of electrical/radio standards!
If you have a weak signal, well that's what you have to work on! Better
antenna for that channel, pointing the right way (remove any hills or
skyscrapers that are in the way!), don't live under a landing flight path or
with a busy highway with metal vehicles whizzing by right in the sight line
between you and the TV station and you should be OK analog or digital.
Good luck.