The official final DTV Table Of Allotments/channel change thread - Page 6

I highly doubt it.

I suspect FCC "authority" for TV Marti is no more than a formality and it doesn't show on any FCC database that I have seen, unless it is hidden somehow and I have missed it.

Interesting thread (hadn't read it in awhile). It seems that our ch 34, currently broadcasting digitally on ch 4 will revert to ch 34. This means I might be able to get a smaller high VHF/UHF antenna (CM4228 maybe). Our other stations are using 7, 8, and 42. This brings up a question, well more of a clarification really. I guess digital chs 7 and 8 can be in the same area without interference.

The FCC rule about adjacent channel allocations, as I understand it, is dependent upon the transmitting antennas for the two stations being in the same, or virtually the same, physical location.

These are located on the same hill.

I have another odd question:

What will the net benefit be when all of these transmitters go off the air in Feb 2009? Will there be a noticeable drop in interference? There should be a noticeable drop in side-channel (at least when channels are no longer abutting).

I noticed in the FCC files that most of the transmitters will end up at approx half their current power. I'd think with fewer signals at generally lower power we ought to realize a noticeable benefit on many channels.

Am I right?

You will have less interference, at least for a short time. If the FCC gets their way and opens up the white space to wireless, license free devices, like they want to do, the interference will be worse than what it is now.

Are you saying that digital transmitters will generally cut their power after analog shutdown? I don't think I've ever read that before. Can you give a reference?

It is true that digital transmitters generally use less power than analog ones. In fact, I think digital usually uses even less than half the power. Around here, some stations broadcast at an ERP of 5000 kW analog and 1000 kW digital (both on UHF channels), with supposedly equivalent service areas.

After the analog transmitters shut down, there will be a lot less total RF energy feeding into people's receivers, which should reduce problems with intermodulation etc.

I've seen a chart a few times showing the channels and their max powers. Can't dig it out of my history Time to dig... dig, dig... all day long... dig dig dig while I sing this song...

http://en.wikipedia.org/wiki/List_of...rvice_Stations


It's all through the FCC data. For example, in my area WWCP is going to switch back to their analog channel 8, at which time they will cut channel 8's power from approx 360 kw to 180 kw.

Nobody is going to be transmitting above 1000 kw. Which is a huge drop-off, especially for some of the upper UHF channels.

It will be interesting to see what comes of this. Mostly I suspect it will mean building more translators.

As I recall, ATSC receivers can have a lower raw signal-to-noise ratio at the antenna input, and still produce a usable picture, than is the case with NTSC receivers. People have posted technical details in this forum, but I don't have any links handy.

Therefore, digital transmitters don't need as much power as analog ones, in order to serve the same territory. If they all had similar power levels to analog transmitters, there would be serious co-channel and adjacent-channel interference problems in many areas.

My main hope is that we'll see a significant drop-off in interference. I had read an item about how during the Northeast Blackout in 2003 that a number of channels were more easily receivable because interfering channels a state away lost their power.

In my case, in PA, I'm hoping that when WATM shuts down its 23 analog signal that its 24 digital isn't as beaten up.

N+1 stations always take a beating because the analog is the lower channel. NTSC uses the upper side of the carrier while ATSC uses the lower side of the carrier and the two signals interfere with each other pretty bad when the analog is the lower channel and ATSC is the upper channel in a first adjacent situation with lower power density levels. The FCC made a conscience attempt to NOT do that, but with limited spectrum in some areas, in some cases they didn't have a choice.

That interference should clear up nicely post transition.

Groovy. Thanks for the confirmation.

This is an apples and oranges comparison. The 316 kW ERP on analog is peak power, the DTV signal is going to be measured as average power. There are approximations of a near 4 to 1 ratio peak/avg, but I'm no physicist.

That explains a great deal about the adjacent channel interference I've seen. Thank you.

Except that it's incorrect. Both NTSC and 8-VSB use the upper sideband.

http://www.broadcast.net/~sbe1/8vsb/8vsb.htm

Ron

You better recheck your sources, doc.

Are you saying the link I provided is incorrect?

Ron

No, the information is incorrect. NTSC does use upper side of a double sideband reduced carrier and ATSC uses the lower side of a double sideband reduced carrier. I deal with both everyday.

You're kidding right? You're saying that a paper written by a Harris Broadcast Systems employee and submitted to the Society of Broadcast Engineers is incorrect? How about some real evidence to prove your totally wrong point (beside "I work at TV station").

Ron

Here's some spectrum analyzer plots taken by Bob Chase of KHWB.

http://www.avsforum.com/avs-vb/attac...chmentid=43178

On every DTV signal, it's obvious that the pilot is at the lower edge of the channel. Since the pilot is created by adding a DC offset to the 8 modulation levels, it is at the same frequency as the suppressed carrier. The plots clearly show that 8-vsb utilizes the upper sideband.

Ron

I don't see how the graphs or any of the explanations above show that an 8VSB broadcast signal is more susceptible to degradation from an analog channel below it rather than from one above it. No appreciable signal from the adjacent NTSC transmitter above or below spills into the plot of the subject 8VSB transmission.

FWIW, I'm in a market with five digital (edit)"+1s" (14A/15D, 26A/27D, 45A/46D. 50A/51D, 56A/57D). I don't have any digital (edit)"-1s" and have never had to deal with any. I have always considered myself lucky to be in such a situation because I can substantially attenuate the strong, lower adjacent NTSC visual carrier with inexpensive bandpass filters (BPF-UHF used to cost under $20 each before they were discontinued), since it is over 5Mhz below the upper adjacent 8VSB pilot, whereas I have read that other antenna installers whose setups were afflicted by strong upper adjacent NTSC carrier have had to use more expensive ($200), Blonder Tongue MWT narrow notch traps, even at VHF frequencies, and I don't know if they are narrow enough to be useful at UHF frequencies.

I have read that some of the consumer, 8VSB tuners use varactor controlled bandpass filters varying in width from ten to 20dB so if that is correct, they may have some an appreciable mitigating effect on lower adjacent NTSC visual carriers (which is where most of the NTSC's RF power is), but negligible effect on upper adjacent visual carriers. I have observed previously that consumer satellite L-band tuners have more bandpass filtering than do the commercial satellite receivers. I'm sure that this is deliberate, to avoid hamstringing a technician who might not want the L-band input filtered in a fixed manner when he can effect what he considers to be optimal filtering externally. I therefore suspect that commercial 8VSB tuners might not have the same bandpass input filtering that consumer-grade 8VSB tuners have.

BTW, comments and letters are still coming to the FCC under proceeding 87-268, some of them are interesting.

Alamo Public Telecommunications Council, licensee of KLRN of San Antonio, TX, objects to Corridor's, owner of KCWX, request to switch it's final digital channel from VHF 5 to 8 with comments on who says low VHF is bad for digital broadcasting? See http://gullfoss2.fcc.gov/prod/ecfs/r...ent=6519538075.

KTBC 7 in Austin, TX, also objects to Corridor KCWX's request to move to VHF 8 writing hey we spent a lot of money on going digital and will be switching to VHF 7; Corridor has been avoiding building a digital facility for nearly a decade so why should be allowed to interfere with KTBC-DT? See http://gullfoss2.fcc.gov/prod/ecfs/r...ent=6519560128. So where will KCWX-DT end up? Stay tuned...

If anyone wants to try to figure out the channel swapping here, KALO of Honolulu wants to swap with another station: http://gullfoss2.fcc.gov/prod/ecfs/r...ent=6519559325. What I don't get is why there would be so much trouble getting digital channel assignments in Hawaii.

Also, the FCC has started to take comments on the third DTV periodic review under proceeding 07-91. Only a few documents show up so far at the FCC site under 07-91. At this rate, the final digital channel assignments for full power stations are not going to come out until 2008.

I hate that reasoning. If anyone were to check the records, they'd find that KCWX did not avoid building a facility; in fact they sought to have a digital assigned to them (albeit on channel 63) and had it denied. That's more than most other stations can say.

They can argue about the other stuff all they want, but that really seems like grasping at straws, even if their other reasoning is sound.

I also am annoyed by how KLRN just dismisses all of low-VHFs interference and reception problems, despite the fact that they are documented and exist just about anywhere a digital low-VHF operates. I, myself, live in a very rural area and despite having near 100% signal strength for all the UHFs in my market, with a dedicated VHF antenna and amp I cannot decode my local PBS, a low-VHF on channel 3, 90% of the time. With the antenna pointed directly at them.

- Trip

I agree. In the ATSC receiver guide

http://www.atsc.org/standards/a_74-w...rigendum-1.pdf

they do not differentiate between interference from +1 or -1 in terms of signal levels that the receiver should be able to tolerate. See Table 4.2 First Adjacent Channel Thresholds.

Here in the SF Bay Area, we have mostly "-1s". 11A/12D, 26A/27D, 32A/33D. 38A/39D, 44A/45D and 48A/49D. There's also a couple of "+1s". 19D/20A and 43D/44A.

Ron

We seem to be using the "+1" terminology from different perspectives. I have been using the term "+1 assignment" to refer to digital assignments that are one channel above the corresponding analog assignments. You are using "+1" in identifying a source of analog interference that is one channel above the digital.

I probably was more likely to view the interference situation from the perspective of its affect on the analog channel rather than vice versa because that is what I had to deal with as a master antenna system serviceperson who maintains analog headends. If the preponderance of uses of the term "+1" in related FCC documents is of the relationship of an interfering channel to the subject digital channel, rather than of the relationship between the transition channel assignment and the original analog assignment, then I may wind up confusing matters by using it in a manner that is inconsistent with its most prevalent use.

My cerebral survey of digital transition assignments tallys that large markets tend to get as many assigned, contemporaneously transmitted digital channels that are one channel above the original analog channel as are possible. I had assumed that having a digital and analog pairing with the analog below and the digital above was more benign and as such, it made economic sense to favor the larger markets with such temporary relationships, but again, because I don't have a single "digital lower/analog higher" pair in my market, I can't support that speculation with any experiences I have had in daling with such interference.

Here's an analysis concerning the possibility of interference from 'white space' devices.

http://www.tvtechnology.com/pages/s.0072/t.7434.html

The FCC laboratory has been testing prototype devices and will release a report soon.

Where will these devices be practical? In the population dense metro areas, there will not be very much white space. In the rural areas they may be practical but the potential for interference is greater there. I 'm guessing a nearby low power white space device will easily 'out shout' a TV station 40 miles distant.

--- CHAS

I like his solution (in the last paragraph):

"Rather than sandwich UD and DTV signals into the remaining broadcast spectrum (Channels 2-51 after Feb. 17, 2009) I favor some partitioning of spectrum, and to do that would mean repacking DTV channel allotments. This drastic step may be the only way to save terrestrial broadcasting from hopeless interference from unlicensed devices spread across the broadcast spectrum and across the coverage area of DTV stations. This is not a matter of if, but when repacking must be done, I believe."

Ron

KEOMI is correct. NTSC power, as measured at the output of the transmitter, is PEAK power measured at tip of horizontal sync. It is measured with no video content, no chroma and no set-up (aural is measured separately). ATSC is AVERAGE power measured across the channel bandwidth. Video content has no bearing because when looking at the signal on a spectrum analyzer, there is no difference between "video" and "noise".

FoxEng - Re-read your theory.

"A simple inspection of Figure 5 reveals the high degree of redundancy in our double sideband AM spectrum. The various sidelobes are simply scaled copies of the center spectrum, and the entire lower sideband is a mirror image of the upper sideband. This allows us to discard almost the entire lower sideband and all of the sidelobes in the upper sideband. The remaining signal (upper half of the center spectrum) can be further cut in half by virtue of the Nyquist Theory, which states that only a 1/2 frequency bandwidth is required to transmit a digital signal at a given sampling rate." Dave Sparano - Harris

I worked with Dave when he was at Thales (now back at Harris) and he is one smart cookie.

Yes, I agree .... If they do "wise up" on this, I wonder how much bandwidth would be needed/used by the UWD's ? Would 4 or 5 channels be enough, including for future "demand"?

I would rather have the UD's confined to say, ch 2-6, but I'm guessing they'd probably want to use UHF for smaller antennas --- Perhaps repacking broadcast DTV into something like ch 2-46 might perhaps be along the right lines, or, I wonder would they need/want more room for the UWD's ....

Here in El Paso KFOX's analog channel is 14 and digital is on 15. The analog channel is filled with short horizonal lines of static. After some big storms last summer it cleared up and I went to a neighbor's to confirm my suspicion that the digital signal was off the air. As soon as digital 15 came back on the static resumed. Oddly, the static is not as bad on older TV's, I suppose they put in better OTA tuners back then. My late model JVC S-VHS recorder is useless on channel 14. I bought a variable attenuator but would have to reduce the signal to the point of being very snowy to loose the static. The Spanish channel KINT is just the opposite situation with the digital signal on 25 and analog on 26 and shows no problems. I will just have to wait until I can convert to HD before 2009.