[opendtv] Re: STATEWIDE DTV TEST

  • From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Sat, 20 Dec 2008 15:26:14 -0800

So, propagation at 85 mHz is similar to propagation at 770 mHz?  And, there
is no to little difference between both on the ability to penetrate or go
around obstructions?

You will go to great lengths to support dumb positions on things you barely
know enough to opine about.

John Willkie

-----Mensaje original-----
De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de Albert Manfredi
Enviado el: Saturday, December 20, 2008 3:05 PM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [opendtv] Re: STATEWIDE DTV TEST


Dale Kelly wrote:
 
>> I'd worry too. Especially because WPVI analog,
>> on Ch 6, is transmitting an ERP of 74.1 KW, whereas
>> in digital, they are scheduled for 7.56 KW, on the
>> same tower. That's a 9.9 dB reduction in power.
>
> Equivalent power for analog to DTV is not 1:1. The
> analog picture power level is about 6db lower than
> it's peak power level, where the extra 6db is used
> to transmit the synchronizing pulses. Since those
> sync pulses are not part of the DTV signal, an
> equivalent DTV power level for your example would
> be about 18.5KW. In this case the channel 6 DTV power
> is still down 3 to 4 db below equivalency, which is
> certainly problematic
 
That was my point. A 6 dB reduction in power, digital compared with analog,
should result in similar reception range. A 10 dB reduction in power, when
the analog is already barely receivable, is asking for trouble.
 
I already posted on here that in the Balt and Wash markets, the VHF DTV
stations will be operating between 12 and 18 dB BELOW where their analog
levels are now.
 
This is all part of the same reality I've been trying to point out for some
time. In spite of the "common wisdom" that VHF is easier to receive, it
looks like some of these ATSC VHF stations are trying to make it be exactly
the opposite.
 
By the way, it's also instructive to know just how difficult it is for Cliff
to receive analog VHF at his location. In any other OTA country, there would
be a repeater tower closer to where he lives. Over here, his reception
problems are attributed to 8-VSB.
 
Bert
 
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