-
Get involved.
We want your input!
Apply for Membership and join the conversations about everything related to broadcasting.
After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
If you use a disposable or false email address, your registration will be rejected.
After your membership is approved, please take a minute to tell us a little bit about yourself.
https://www.radiodiscussions.com/forums/introduce-yourself.1088/
Thanks in advance and have fun!
RadioDiscussions Administrators
Relationship between DTV power levels and antenna height
- Thread starter alg2468
- Start date
50kw vs 1MW is a big difference...especially at the fringe area....Antenna height makes all the difference regardless of power...depending on surrounding terrain
There are several factors taken into consideration. Whereas field strength is field strength, no matter what the frequency, there are considerations made for signal propagation for VHF vs. UHF, analog vs. digital, line of sight or with terrain. As the FCC always has since the beginning of OTA TV, coverage calculations makes some assumptions beyond the transmission site, such as; the receive antenna is X-gain, horizontally polarized, mounted 30 feet off the ground, line of sight to the TX location. Or, calculated based on the Longley-Rice method, which includes terrain into the calculation. If you'd like to see some free examples of DTV coverage in your area, visit tvfool.com. I think you'll find it interesting.
My guess is that "theoretically," digital TV signals can be received with perfect quality with a lower signal-to-noise ratio than analog signals. That theory is BS because it assumes perfect signals in both cases, and with the same antenna.
Trouble is, many, if not most residences in urban and suburban areas are not allowed outside antennas thanks to HOAs and apartment leases. That means the antennas available have less gain and less directivity. The latter is the killer. Multipath means ghosts in analog, and no signal at all in digital.
In many cases, high-powered FM stations overload the TV tuners and/or the antenna preamp. I found this when I lived in Phoenix and was 5 miles from the South Mountain transmitters. An FM trap was mandatory to get much of anything on VHF. Now that I'm 30 miles away, in Mesa, it's not an issue.
The FCC needs to restore the analog power levels (100 kW 2-6, 316 kW 7-13, 5 MW UHF) for digital transmissions.
Oh they most definitely should increase digital power levels to their old analog equivalents but that will likely never happen as those days are long gone. If it were up to the broadcasters, they would shut off their blowtorches in a hot second, lie back and rake in those cushy retransmission fees from the cable cos and enjoy a much lower electricity bill to boot. But as it stands, those pesky grey haired dinosaurs at the FCC require them to throw out an OTA signal to the unwashed masses and freeloaders (like me). At least for now, they do.
So, they put out "just enough" signal reluctantly and call it a day.
Height is the driver of coverage much more so than power is. If you believe the models, a 1000 kW signal at 365 meters is equivalent to a 316 kW signal at 610 meters. As long as you have line of sight, power is a lot less relevant after a certain point. With line of sight, I easily got a 17.9 kW signal, indoors, at 53 miles.
It's not BS at all. First of all, power is measured differently in analog versus digital. Analog was peak power, while digital is average power. The only time a station at 5000 kW actually made that power was when the screen was solid black. On average, power was closer to 2000 kW. Meanwhile, you can flip it around; the peak to average ratio for ATSC is about 6 dB, which means the peak power is about 4000 kW. In truth, the numbers really aren't that different; the difference between 1000 kW and 2000 kW is 3 dB.
So the power levels are very close, but then there's the difference between analog and digital. The analog Grade B level is 64 dBu, while the noise-limited contour is 41 dBu. That is, the necessary signal is 23 dB weaker with digital than analog. So the power remained the same, but the signal became much more resilient. So say you really are 3 dB weaker in ERP, that means you still have a 20 dB improvement over analog.
https://www.fcc.gov/media/over-air-reception-devices-rule
Many (not all) people can have an outdoor antenna and choose not to.
Unfortunately, this is a problem with modern receivers. Analog TV tuners had FM traps in them and digital receivers generally don't, from what I understand. But putting an FM trap in the line usually solves that problem.
The VHF power levels do need to go up in a sense, but the UHF power level is adequate. I already explained UHF; on VHF, the theoretical max power levels are fine (45 kW on low-VHF, 160 kW on high-VHF), but due to the way the protections are done, the power levels are typically much lower than they probably should be.
There was an attempt to fix the VHF power levels after the transition, but it never went anywhere. Broadcasters said they preferred to handle cases like these by seeking waivers one-by-one instead of by changing the rules to permit more power.
- Trip
Thanks for the clarifications, trip. Will the FCC be addressing this as part of the repacking, or maybe later?
K
K.M. Richards
Guest
I'll take a market you're familiar with, Rob (Los Angeles) to at least partially disprove that theory or opinion, whichever you meant it to be.
KTLA/5 sells local advertising on their subchannels (Antenna on 5.2 and This on 5.3). So does KDOC/56 on MeTV (56.3).
KSCI/18 is running something like a dozen ethnic subchannels, each one programmed 24/7 by lease. Similar arrangements are in place for KXLA/44 and KRCA/62. There are also scattered leased religious subchannels on various stations in the market.
That's all extra revenue to the stations, and doesn't increase the power bill at Mt. Wilson by very much.
I presume you -- like myself -- are getting at least 30 channels worth watching from the arrangement, once you subtract the shopping, foreign language and religious services?
Can't say anything for sure, but it doesn't look likely. The rules for the repacking basically continue the status quo; a station which opts to be paid to move to VHF will be replicated in the same way as the DTV transition and then will be able to seek waivers to boost power one-by-one. Which is what the broadcasters said they wanted when the rules were up for discussion.
- Trip
As a retired Television Engineer, I can tell you that you are mistaken if you believe that the local TV station does not get involved with cable and satellite reception issues.
At my station, we watched our channel on analog and digital cable as well as on Dish and DirecTV. At the first sign of a problem, our Engineers would report the issue to the cable/satellite provider and demand immediate attention.
All too often, the cable company would tell the viewer that the problem was with the TV station and not the cable company. Fortunately, the satellite companies would put a message on the screen to inform the viewer that they are aware of the problem and are working to resolve it.
I wonder if other stations are also as dedicated in the reverse, i.e., worrying about their OTA signal as opposed to their cable/sat signal? Following the DTV conversion I had nothing but trouble with the three high-VHF stations in my market, submitted detailed problem reports to all three, got not one response and their signal is still very sensitive to failure although it is marginally better than then. I sure didn't see any urgency on their behalf.
You missed my point Frank. Maybe because I wasn't clear enough.. Cable and satellite subscribers pay cable and satellite providers to get them reliable TV signals to their homes. This takes a great part of responsibility for QOS away from local TV stations. By promoting OTA TV, now stations are taking-on responsibility (at least from the viewer perspective), of the installation quality of that TV signal to the home.
I'm not sure if you were retired by the time the DTV conversion came around in 2009, but I was in the thick of it. Between pissed off viewers trying to use some old 300 ohm rabbit ear antennas, to a viewer who bought a $29.99 sick-on window antenna from a drugstore end cap that lived 40 miles away from town, it was a hectic five or six years listening to various irate viewers who wanted my engineering staff to go to their home and make OTA TV work to their satisfaction. In some cases we did and depending on the situation, had no recourse to tell the viewer they would probably need to buy basic cable.
Last edited:
See..Landtuna makes my point.
K
K.M. Richards
Guest
Again, speaking from an unfair perspective in market #2 ...
I've had conversations with the engineering staff at about a half-dozen stations here since the conversion, including the Fox-owned and NBC-owned stations, plus the owner/engineer/bottle washer at one of the LPTVs. They have all been very responsive, they've consistently asked me for additional information about reception problems (most of my issues have been when the encoder for a stream gets "locked" in a display mode, preventing me from seeing a normal picture).
Of course, that level of response and attentiveness is going to vary from market to market, and from station to station (tipping the hat to the late Mr. Bowie on that last).
Done.
One station I watch with an antenna had so many complaints with their high VHF signal that they switched back to the UHF channel they had used before they were required to turn off the analog signal. Not everyone is so lucky. I was too far away to ever receive the VHF signal but the UHF usually does well even with the indoor antennas I use.
And now with repacking how many stations are going to do the reverse?
- Status