[opendtv] Re: STATEWIDE DTV TEST
- From: Albert Manfredi <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sat, 20 Dec 2008 18:04:33 -0500
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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