[opendtv] Re: USDTV demos at NAB
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 29 Apr 2004 16:39:44 -0400
John, dipole gain comes in because UHF receiving antennas
can compensate in large measure for the more rapid
attenuation of UHF signals. I think I'm disagreeing
that indoor reception of VHF is necessarily easier than
indoor reception of VHF, which is why I was wondering
why you tried to discount the fact that a receiver was
available even in 2001 which could get solid indoor
reception of 8-VSB from 17 miles away.
Let's do the numbers on your numbers, just so this can
be clear. I'm using 50 mile range, a required 25 dB
margin, and free space attenuation for this comparison.
Your Channel 23, 525 MHz, 1.23 MW transitter's signal
is attenuated 125 dB at 50 miles. Assuming a 25 dB
margin, a receiver with unity gain antenna will see
-59 dBm of signal. Not bad.
Your Channel 6, 83 MHz, 100 KW transmitter's signal
is attenuated 109 dB at 50 miles. Assuming a 25 dB
margin, a receiver with unity gain antenna will see
-54 dBm of signal.
Now, how hard is it for a UHF antenna to make up
that 5 dB signal difference? Not very. UHF antennas
can afford to be higher gain, because the elements
are much closer together!
I think that was Doug's point.
Bert
> -----Original Message-----
> From: John Shutt [mailto:shuttj@xxxxxxxxx]
>
> Doug,
>
> You lost me completely. You mean we've been wasting all that
> money on power bills for our UHF 23?
>
> 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?
>
> John
>
> ----- Original Message -----
> From: "Doug McDonald" <dtvmcdonald@xxxxxxxxx>
>
> > Not really. VHF uses lower powers because
> > a tuned dipole antenna has a receiving area
> > inversely proportional to the square of the frequency.
> >
> > However, at UHF it is far easier to get gain; a UHF
> > antenna as big as a channel 2 dipole will have a truly
> > gigantic gain and will pick up the same actual
> > fraction of the ERP as will the Ch. 2 dipole.
> >
> > Also, UHF signals penetrate modern houses with
> > foil heat barriers in the walls much better than
> > VHF, especially low VHF, because there are several
> > waves in the size of the average window at UHF, only
> > one at high VHF, and less that one on Ch. 2.
> >
> > > VHF is much less line of sight.
> >
> > This is true. Digital Ch. 3 needs far more power than
> > it is getting.
> >
> > Doug McDonald
----------------------------------------------------------------------
You can UNSUBSCRIBE from the OpenDTV list in two ways:
- Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
Other related posts:
