NBC Boston info

Trip Ericson webmaster@rabbitears.info
Mon Nov 7 14:43:14 EST 2016

As an engineer, I disagree because you're comparing apples and oranges.
Analog power was peak power.  You only hit 5000 kW analog when a solid
black picture was being transmitted; the rest of the time, the signal was
lower than that.  ATSC digital power is average power.  Since ATSC's peak
to average ratio is about 3-5 dB (with the maximum, very rarely, being 7
dB), the typical peak power of a 1000 kW ATSC signal is closer to 2000-3000
kW.  That's a 3 dB difference on UHF.

And then that doesn't take into account the difference in receive
thresholds.  A perfect digital decode requires an SNR of 15 dB, give or
take a bit of margin to account for fading.  A decent analog picture
required something like 30 dB SNR, and a perfect picture was closer to 50
dB SNR.  So the power has gone down, at best, 6 dB on UHF, but the margin
for reception has dropped at least 15 dB, depending on how clear you want
to make the picture before calling it acceptable.

The real difference is that people were willing to put up with very poor
pictures in analog and low-VHF was more forgiving of rough terrain.  Even
if you ramped up the power and put digital stations back on low-VHF, many
of those people still wouldn't have service because the signal was never
that great to start with.

Here's a good example.  WGBX's analog was at 1100 kW.  Its digital is now
500 kW.  That's slightly more than 3 dB of difference.  They're basically
equivalent when you account for the difference between peak and average
power.  An outdoor antenna should receive WGBX, notwithstanding
interference from other stations, out to at least Webster, Charlton,
Rutland, and Ashburnham, notwithstanding a few really serious
terrain-caused holes, and see increasing terrain blockages west of that.

- Trip

On Mon, Nov 7, 2016 at 11:25 AM, M.Casey <map@mapinternet.com> wrote:

> 22,40,57, 50/51 & Springfield's version of Channel 3 are on OTA TV. 40 &
> 57 have , sort of, a reasonable coverage area. 22 is just fair and suffers
> from low power on RF channel 11. 3 and 50/51 are UHF low power stations.
> The Hartford area stations-3, 18, 20, 24, 30, 61 cover up into the lower CT
> River Valley on OTA TV. But, to be fair, there are few places in the area
> between Worcester and 15/20 miles east of the Connecticut River that have
> OTA TV reception. That's a large geographic area that, for the most part,
> had some coverage from OTA TV stations before digital.
> I know that some engineers will disagree, mostly because of predicted
> interference (that would rarely occur), but even with closer station
> spacing,  most digital TV stations should have 20-50% of their analog power
> to effectively duplicate their coverage on digital, not 5-20% (or even much
> less in many cases). Today's coverage problem (with the, mostly, 5-20% of
> analog power limits), is not quite as bad in flat terrain areas like most
> of Florida, but much worse in mountainous areas, like most of New England.
> Mark Casey
> -----Original Message----- From: A Joseph Ross
> Sent: Sunday, November 06, 2016 1:09 AM
> To: boston-radio-interest@lists.BostonRadio.org
> Subject: Re: NBC Boston info
> Nothing on OTA TV west of Worcester?  What about the Springfield stations?
> On 11/5/2016 11:23 PM, Mark Laurence wrote:
> I don't think anyone on the Cape can receive TV without cable, and I know
> for sure that there's nothing on OTA TV west of Worcester.
> -----
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