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Re: [HDTV-in-SFbay] Re: after the apocalypse

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  • Ron Economos
    Free space path loss (in air or vacuum) is: Loss in dB = 36.6 + 20 log f (in MHz) + 20 log d (in miles) or Loss in dB = 32.4 + 20 log f (in MHz) + 20 log d (in
    Message 1 of 20 , Feb 1, 2006
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      Free space path loss (in air or vacuum) is:

      Loss in dB = 36.6 + 20 log f (in MHz) + 20 log d (in miles)

      or

      Loss in dB = 32.4 + 20 log f (in MHz) + 20 log d (in kilometers)

      For KGO-DT, the free space loss at channel 24 (533 MHz) is 9.6 dB
      greater than at channel 7 (177 MHz). Assuming they run 316 kW when
      they move their digital transmitter back to channel 7, they will have a 7.1
      dB advantage over their current 561 kW transmitter on channel 24. In
      other words, their signal at 316 kW on channel 7 would be equivilant to
      a 3 Megawatt transmitter on channel 24.

      Ron

      Richard Swank wrote:

      > I would guess if you receive KNTV-DT on channel 12 (Rf) you will receive
      > KGO-DT on channel 7 (Rf) or KQED ch-9 without a problem. VHF
      > propagation is
      > better than UHF as the wavelength is quite a bit longer and therefore it
      > takes larger objects to reflect it or attenuate it. Just the atmospheric
      > air attenuation of Rf signals is a function of the wavelength,
      > basically the
      > Rf strenght of the transmitted signal attenuates to 1/2 at every
      > wavelength
      > it travels from the antenna source. Ch-12 wavelength is around 33 inches.
      > So by a little over 5' from our antenna the signal strength is 1/4th
      > of the
      > 101.3KW we are transmitting and every 33" from there on it is 1/2 again.
      > Ch-40 wavelength is less than 10" so this attenuation occurs much
      > faster as
      > it travels through space.
      >
      > This is why the FCC maximum NTSC power for a High band VHF transmitter
      > at a
      > height under or equal 2000' is 316KW and at the same time that
      > "EQUIVALENT"
      > UHF power is 5000KW. DTV power levels are average power and about 1/5
      > those
      > of these peak NTSC power levels. So DTV power maximums for UHF are
      > currently 1000KW but interference maxification studies can modify this
      > some.
      >
      > For instance KNTV did DTV maximization studies prior to our move to Mt.
      > Bruno and although our NTSC is operating at an E.R.P. (Effective radiated
      > Power) of the 316KW we were able to obtain a license for the DTV
      > transmission to be an ERP of 101.3KW. This means our equivalent DTV
      > signal
      > strength is somewhat larger than our NTSC signal strength in most
      > locations.
      >
      > My assumption is that KGO-DT will also maximize power levels based on
      > interference to other broadcasters and since they have owned ch-7
      > since day
      > one they will likely be able to operate at higher than the 1/5th NTSC
      > power
      > level.
      >
      > Since these transmitters operate at about 35-40% efficiency levels at best
      > you can probably figure that propagation improvement is not the only
      > advantage to being a high band VHF. Monthly PG&E charges are also much
      > lower. DTV transmitters in the high band VHF operations will usually be
      > solid state instead of tube as well. More reliable and considerably less
      > expensive to maintain.
      >
      > Yes, low band VHF (ch 2-6) propagation is even better than high band VHF,
      > for the same reasons, but since bit error rate is "very" critical to DTV
      > reception low band VHF to this point hasn't proven very good. This is
      > mostly due to things like ignition noise. DTV viewers certainly wouldn't
      > like their picture to pixelate and go black every time a truck or car
      > drives
      > by or the neighbor mows his lawn or runs his blender. If receiver
      > manufactures could resolve the error problem most current NTSC VHF
      > stations
      > would remain on their NTSC channel when DTV takes over.
      >
      > I do believe that broadcasters will be forced to kill NTSC and make the
      > magic switch to their new DTV channels at 00:01 on Feb 17th, 2009. During
      > the preceding weeks to this it may mean that neither the NTSC or DTV
      > reception between 1:30am and 4:30am will be any good on these channels
      > that
      > conflict as the stations perform required FCC testing but that is the cost
      > of progress so to speak.
      >
      > Most older high band VHF NTSC antennas and transmitters are not flat
      > enough
      > (=gain over the 6 megahertz channel band) for good DTV transmission. They
      > would probably cause an effective built in error rate to be transmitted by
      > the broadcaster. This in turn would make the viewer reception much more
      > difficult and cause undue problems to the station. I would therefore
      > expect
      > most broadcasters like KGO to replace their antennas between now and 2009.
      > NTSC works just fine on a DTV antenna so except for the couple of days the
      > actual installation of the new antenna takes nobody will notice the
      > change.
      > NTSC broadcasters pre-distort our signals to compensate for antenna and
      > transmitter non-linearity. This works very well in the analog world but
      > this trick is not an option for DTV.
      >
      > I can forsee "new" local DTV channels coming on-line once the current
      > double
      > locals channels are not in exsistance. Maybe not in SF as there is so
      > many
      > stations already but there will be freed up UHF channels so it's possible.
      > Not all the channels being freed up are above the ch-50 maximum. Of
      > course
      > the FCC plans on auctioning these off for other services and for big
      > $$$$$$$.
      >
      > So I wouldn't call Feb 17th 2009 an apocalypse. It will be an interesting
      > time for viewers and broadcasters alike however.
      >
    • thekatdude
      Same here, I can get all the SF channels, but no 11 since the X-mtr left SJ. Strange thing is I can get the digital for KSBW is the conditions are right. ...
      Message 2 of 20 , Feb 1, 2006
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        Same here, I can get all the SF channels, but no 11 since the X-mtr
        left SJ. Strange thing is I can get the digital for KSBW is the
        conditions are right.

        --- In HDTV-in-SFbay@yahoogroups.com, "Michael Portuesi"
        <mportuesi@...> wrote:
        >
        > --- In HDTV-in-SFbay@yahoogroups.com, "Richard Swank" <rswank@p...>
        wrote:
        > >
        > > I would guess if you receive KNTV-DT on channel 12 (Rf) you will
        receive
        > > KGO-DT on channel 7 (Rf) or KQED ch-9 without a problem.
        >
        >
        >
        > Considering I don't receive KNTV-DT at all from my location, I'm not
        > optimistic about KGO-DT's move to VHF after the analog shutdown.
        >
        > To be fair, KNTV is on Mt. San Bruno and that's my real problem with
        > receiving it. But it really would be nicer if all the local stations
        > were broadcasting UHF. It would make it a lot easier for us to receive
        > all the stations if UHF were all we had to focus on receiving.
        >
        > I have a partner who is very adamant about not having a rooftop
        > antenna. While I might be able to sell one fairly small UHF outdoor
        > antenna, having to install two antennas (or one honking huge combo
        > antenna) is a big issue for me. Likewise, I currently use a Silver
        > Sensor indoors, and it only receives UHF.
        >
        > I do wish the broadcasters would think about the viewers when they
        > make their channel allocation decisions. Having two frequency bands
        > rather than one is a pain.
        >
        > Michael Portuesi
        >
      • Swank, Richard (NBC Universal, KNTV)
        Where do you live? ... From: thekatdude [mailto:thekatdude@yahoo.com] Sent: Wednesday, February 01, 2006 11:41 PM To: HDTV-in-SFbay@yahoogroups.com Subject:
        Message 3 of 20 , Feb 2, 2006
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          Where do you live?
          -----Original Message-----
          From: thekatdude [mailto:thekatdude@...]
          Sent: Wednesday, February 01, 2006 11:41 PM
          To: HDTV-in-SFbay@yahoogroups.com
          Subject: [HDTV-in-SFbay] Re: after the apocalypse

          Same here, I can get all the SF channels, but no 11 since the X-mtr
          left SJ.  Strange thing is I can get the digital for KSBW is the
          conditions are right.

          --- In HDTV-in-SFbay@yahoogroups.com, "Michael Portuesi"
          <mportuesi@...> wrote:
          >
          > --- In HDTV-in-SFbay@yahoogroups.com, "Richard Swank" <rswank@p...>
          wrote:
          > >
          > > I would guess if you receive KNTV-DT on channel 12 (Rf) you will
          receive
          > > KGO-DT on channel 7 (Rf) or KQED ch-9 without a problem.
          >
          >
          >
          > Considering I don't receive KNTV-DT at all from my location, I'm not
          > optimistic about KGO-DT's move to VHF after the analog shutdown.
          >
          > To be fair, KNTV is on Mt. San Bruno and that's my real problem with
          > receiving it. But it really would be nicer if all the local stations
          > were broadcasting UHF. It would make it a lot easier for us to receive
          > all the stations if UHF were all we had to focus on receiving.
          >
          > I have a partner who is very adamant about not having a rooftop
          > antenna.  While I might be able to sell one fairly small UHF outdoor
          > antenna,  having to install two antennas (or one honking huge combo
          > antenna) is a big issue for me.  Likewise, I currently use a Silver
          > Sensor indoors, and it only receives UHF.
          >
          > I do wish the broadcasters would think about the viewers when they
          > make their channel allocation decisions.  Having two frequency bands
          > rather than one is a pain.
          >
          > Michael Portuesi
          >




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