[opendtv] Re: Fw: Re: FCC Opens TV Spectrum for Broadband Use
- From: Cliff Benham <flyback1@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 05 Dec 2010 22:47:27 -0500
On 12/5/2010 7:45 PM, Albert Manfredi wrote:
Cliff Benham wrote:
When WLW, Cincinnati was broadcasting 'CLEAR CHANNEL" at 50KW
after WWII they were transmitting with the 50KW driver stage
for the 500KW final that was not in use after the FCC limited
AM power to 50KW.
With the 500KW final on air, WLW could be received from coast
to coast and was then known as 'The Nation's Station'.
Didn't know that. Very interesting. WWVB tries to do the same coast to coast
thing from Boulder, for time and date, at 60 KHz, but I don't know what ERP
they use. Isn't always reliable.
WWVB is weakest on the East coast according to a note in the wiki
article http://en.wikipedia.org/wiki/WWVB
It has 2 antenna systems and 3 transmitters in use depending on
maintenance schedules, etc. When transmitting with both antennas,
the ERP is 70 KW, with just the north antenna, 50 KW, with just the
south antenna, 27 KW.
Imagine assigning 500 KW ERP to a mere 10, or even 30, KW of bandwidth! And
here we have VHF TV stations, supposedly big sticks, operating at 5 KW ERP for
6 MHz of bandwidth.
You have to take into account that the RF at very low frequencies is a
ground wave, not being reflected from the ionosphere, but traveling
directly over the ground from the transmitting antenna to the receiver.
Medium wave and short wave signals bounce between the earth and the
ionosphere multiple times before reaching a receiving antenna at a great
distance.
Above 30 MHZ, RF signals travel in more or less straight lines and can't
bounce off the ionosphere, which does not reflect those higher frequencies.
This is why VHF TV stations were limited to line of sight operation at
ERPs of up to 1MW while UHF stations could radiate up to 5MW ERP.
Otherwise the UHF signals would not cover the same areas as VHF.
This driver and antenna had a pass band of 30KHz and WLW billed
itself as the 'High Fidelity Voice' of AM radio. While the
sidebands do contain energy out to 15 KHz each side of the
carrier, the energy diminishes greatly and is far less apparent
the further from the carrier one measures.
True, depending on the audio material. On the other hand, there's going to
usually be enough there to create annoying whistling at night, on analog AM.
Most good AM Hi-Fi receivers include a 10KHz whistle filter to eliminate
this annoyance. It's a simple parallel resonant coil and capacitor wired
in series with the audio out point of the detector.
Very effective and easy to add to a radio tuner.
However it does not cause anything like the kind of interference
to reception of other AM stations that HD radio causes. HD causes
a wide band blanketing effect [white noise] which extends at the
same high level out to + - 15KHz either side of the carrier and
blanks out reception of distant AM stations for hundreds of miles.
Because digital radio and TV deliberately scramble the quantized audio samples,
so as to generate a flat spectrum. To me, that's a good thing, for the digital
channel anyway, because it makes the best use of the channel.
Have you tried HD Radio in the AM band? It sounds fantastic, compared to the AM
analog. But you do need people to quit using AM analog first. For the first few
years, the FCC didn't allow HD radio in the AM band during nighttime hours. I
think they stopped preventing that, though. The best thing would be to stop
analog AM altogether, go all digital, and that way the stations coiuld go back
to their proper 10 KHz bandwidth.
Bert
I have two HD radios, a pocket portable FM and another AM-FM set that
will work in the car and at home.
For me the technical superiority of the HD reception is directly
counterbalanced by the lack of ANY good program material to listen to.
There are no classical music stations using HD radio in the Philly area.
The kind of music available over HD is abysmal and the only other thing
out there is talk radio and news shows punctuated by traffic reports.
What a waste of a possibly great technology.
Cliff
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