NBC Boston info

[M.Casey]

Agreed on the technical points.  A 3db difference in power ratings makes 
sense.
The differences between digital and analog and a poorly designed FCC formula 
for a well designed digital system that over-rates digital signal 
expectation against old analog limits force us to deal with a so-called 
apple and orange comparison.

---The 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."
---agrees with my point:
"most digital TV stations should have 20-50% of their analog power to 
effectively duplicate their coverage on digital"
44's digital power is 45.4% of it's analog.

Of course, there's the problem of VHF stations moving to UHF. After initial 
problems on VHF, and due to the looming repacking, and the FCC letting up on 
power limits as in the LA example below, we may be seeing a reversal to VHF 
to UHF migration to a UHF to VHF migration. Like LA, If Boston Channel 7 was 
allowed 115kw instead of 11.8kw on RF7, they might find it beneficial to 
move their digital signal back to RF7. And, if Boston stations moved back to 
both VHF hi-band and low-band allocations using 30-40% of analog power, then 
many of those folks in mountainous areas like Central & Western Worcester 
County would get back the OTA TV service they lost in 2009.

Maybe when TV was new in the 1940's and 1950's it was a factor, but I 
disagree that any significant segment of analog viewers after the 1960's put 
up with poor signal. I don't know anyone that did. If they got a poor signal 
they either got a better antenna or an outside antenna or bought cable, if 
cable was available. There are thousands of viewers that have been 
dis-enfranchised from OTA TV because of the poorly designed FCC power limit 
scheme for channels 2-13.

The bottom line is the question for the public:
After the conversion to digital, can the viewers still receive most of the 
same stations using the same or similar antenna they had used with analog?

In the cities and suburbs, probably so, farther out in the country, probably 
not.

If not, then digital power needs to be increased, like the example of Ch 11 
& 13 in the Los Angeles market, whose original digital allocated power was 
5% of analog (11,800w), and have now been increased to more than 35% of 
analog (115,000-120,000w) in order to more closely duplicate their analog 
coverage.

Mark

-----Original Message----- 
From: Trip Ericson
Sent: Monday, November 07, 2016 2:43 PM
To: M.Casey
Cc: A Joseph Ross ; Boston Radio Group
Subject: Re: NBC Boston info

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
www.rabbitears.info



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