[opendtv] Re: USDTV demos at NAB
- From: Doug McDonald <dtvmcdonald@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 30 Apr 2004 13:37:18 -0700 (PDT)
--- John Shutt <shuttj@xxxxxxxxx> wrote:
> Doug,
>
> You lost me completely. You mean we've been wasting
> all that money on power
> bills for our UHF 23?
No no no .... the VHF people need more power.
>
> WLNS Channel 6 here in Lansing runs at 100 kW ERP
> and covers an area of
> 31,907 sq. km. We, WKAR Channel 23, run at 1,230 kW
> ERP and cover an area
> of 16,624 sq. km.
>
> Where does UHF dipole gain come in?
>
Those numbers are probably calculated using
dipole antenna, at 30 feet, and assuming a better
noise figure for the VHF preamp. Of course they
also include the greater diffraction over the horizon
efficiency of VHF.
But the great benefit of UHF is indoors in modern
buildings designed to prevent TV receptiion indoors,
by using metal lined thermal insulation everywhere
except the windows. I can see two new apartment
buildings being built from the windows right here
beside me. Both cover everything except the windows
with what is clearly a continuous sheet of aluminium
foil, which will stop radio waves dead. And the
windows are not terribly large.
This means that the windows are smaller than 1/2
wavelength at low VHF and not much bigger than 1/2
wave even at Ch. 13. But they are several waves at the
middle and upper UHF frequencies. An indoor Ch. 6
antenna cannot pick up anywhere near what a dipole
outdoors can. Say -3 dB gain at best. But an indoor
UHF antenna, like a Silver Sensor, can get 6 or maybe
even 10 dB gain compared to a dipole. Say 8 dB. That
total of 11 dB gain difference means that the
a UHF dipole. This means that the Ch. 23 antenna is
getting more power then the Ch 6 one, at the powers
you quote above, pointing at the station of course.
And indoors, the VHF at Ch. 6 is going to suffer badly
from impulse noise, and at 23 that noise will be
vastly down.
Doug McDonald
=====
Doug McDonald
my last name at scs dot uiuc dot edu, not here at Yahoo, please
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