: Understanding OTA DTV Broadcasting Technology in Canada
2007-01-24, 12:12 PM
Ok in simple layman terms 99gecko said the antenna does need to be pointed in the direction where the transmitters are.
If the signal was to come south of you the antenna cannot be pointed west or east it should be pointed south.
Also if you were to look towards that direction at the transmitters and close by you don't have taller buildings or trees etc you should be ok.
2007-06-27, 08:56 AM
just wanted to know what is the maximum signal in db that the a tv can receive in OTA (hd and SD).I have a cable meeter to check the signal.Some pre amp and amplifier have a gain of 22???It seems a little bit high
By the way I cant found the thread where I can see the exact frequency for all the HD channel,anyone can post a link
2007-06-27, 09:08 AM
I remember reading that DTV tuners must be able to receive signals ranging from -8 dBm to -84 dBm. That being said, the bare minimum signal needed for lock is a little higher due to receiver noise (about -73 to -75 dBm) but is always better. Hope this helps.
2007-06-27, 11:00 AM
jtheman, almost all new HDTVs have built-in AGC circuits in their ATSC tuners that are meant to adjust to the signal load. Even so, when first using an amplifier it is sometimes best to put an attenuator in line. It is a safe thing to do. Afterwards if it looks like the attenuator is costing too much signal you can take the attenuator out and check signal strength again.
Regarding amplifiers, the purpose of using them is to combat line loss over long distances by making the signal stronger at the input end. You would never use an amplifier going over a 1 meter coax cable into your tuner because it would certainly overload. You would use an amplifier if the coax cable is about 12 meters or more and is therefore losing signal on the way to the tuner.
You can do the arithmetic to calculate roughly how much signal strength you are getting, how much the coax is taking away, and therefore how much amplification you might need.
Here is a great frequency list:
2007-06-27, 12:29 PM
Finally found it in the spec, A/74 states the dynamic range of DTV signals is -83 to -8 dBm.
2007-06-27, 09:46 PM
thanks for the info guys,I know a lot about amplifier,I work in cable...thanks for the link stampeder they are very appreciated
2007-06-28, 02:36 AM
A/74 states the dynamic range of DTV signals is -83 to -8 dBmThanks for that patrbois, but a warning that we need to be clear that dBm and dBu values for the same signal can be quite different depending on the impedance and other factors, so we need to really think this over to understand OTA ATSC signal strength numbers (usually expressed as a station's contour in dBu) and the numbers you've found for receiver input circuitry in dBm, not to mention an antenna's, amplifiers's, or preamplifier's gain as expressed in either dBd or dBi. :)
Here's a good web link that illustrates how confusing the different values can be, and it has some formulae for computing what jtheman is probably thinking about:Q: What is the difference between dBu, dBm, dBuV, and other units?
A: There is a great deal of confusion when engineers, technicians, and equipment salespersons talk about units of antenna gain and field strength. People in different disciplines of the radio telecommunications industry seem to be speaking different languages and most people are not multi-lingual. This article will discuss units of gain and field intensity and explain how to convert between some of these units when appropriate. http://www.softwright.com/faq/engineering/FIELD%20INTENSITY%20UNITS.html
2008-04-04, 02:23 PM
This thread mostly discusses the actual broadcasting technology with respect to antennas, dB, power, etc., but not much has been said about getting the signal ready to be transmitted. ATSC, the DTV transmission standard applies 8-VSB modulation to the MPEG 2 signal (the compressed A/V feed) prior to "sending it up the tower".
Here is more info about 8-VSB if you are interested:
WHAT EXACTLY IS 8-VSB ANYWAY? (http://www.broadcast.net/~sbe1/8vsb/8vsb.htm)
2008-09-26, 03:10 PM
Industry Canada restricts the noise-limited contour for digitial stations to 89-km, regardless of how big the analog B-contour was for a given station.
Is this limitation only for digital stations, or for all new applications and old allotments were grandfathered. If it is only for digital stations, is this going to change after the analog shutdown in 2011?
2008-09-26, 03:58 PM
Is this limitation only for digital stations, or for all new applications and old allotments were grandfathered.
AFAIK, only for digital stations. There aren't any new analog stations, so that point is probably academic.
If it is only for digital stations, is this going to change after the analog shutdown in 2011?
I was wondering the same thing, but my source on B-TAC says no, the 89-km limit stays post-transition.
At least, that's the plan.
The plan was also that more than a handful of stations would build their transitional digital stations, so who knows?
Other tidbits derived from published BTAC minutes:
- most VHF-low analog stations will be given priority to get VHF-High allocations.
- VHF-High allocations will be given priority to stay on VHF-High.
By the way, none of this precludes CBOT from changing from 160kW max ERP directional to 160kW ERP omnidirectional (or the equivalent parameters for a VHF-High allocation), as this does not extend the radius beyond 89 km. However, this just extends reception northward through sparsely populated territory towards Maniwaki, where there is already a CBC Montreal repeater (albeit unlikely to be digital anytime soon).
2008-09-27, 03:42 PM
tvlurker, are you sure they meant 89 kilometers for countours? I just spoke yesterday with an antenna engineer from one of the Canadian networks who said all the talk now with Industry Canada and the FCC is to raise the signal level of all digital station A contours up into the range of 60 to as high as 88dBu.
2008-10-03, 01:13 AM
are you sure they meant 89 kilometers for countours?
digital station A contours up into the range of 60 to as high as 88dBu
City Grade (formerly known as Grade A contour) coverage in FCC speak is just used, AFAIK, to prove coverage of the nominal city of license. In other words, if you can't provide a city grade signal throughout your city of license, you'd better explain why.
It doesn't say anything about how far away the noise limited contour (which is roughly equivalent to the former Grade B analog contour) can be from the transmitter site. In calculating the noise-limited contour, it appears to me that the FCC just cares about:
- the percentage of covered population that suffers interference to/from other channels.
- how much larger or smaller the contour is than the original transitional contour that the FCC came up with
- which contour is the largest in the market.
- maximum power levels for frequency band, region, and EHAAT
- public and occupational RF radiation safety limits at the transmitter site.
Back to the Canadian discussion: I spoke with my knowledgeable contact, and he said that as far as he knew, the 89-km radius limit will hold for post transition contours, as well.
I think what you may be seeing is recognition that ERPs will have to be higher than previously thought to provide reliable, robust transmission to a large area. So while this could result in higher power levels so that those with 16dBi super antennas ;) can reliably receive beyond an 89-km limit, for the great unwashed, the design limit will stay at 89km. It's just that what dBu level is required to reliably provide service to that radius may have to be higher than previously thought.
2008-10-03, 03:12 PM
recognition that ERPs will have to be higher than previously thought to provide reliable, robust transmission to a large areaYes, that was the exact context of what I was hearing is the issue - a rethink of previous ERP expectations, especially for penetrating large urban areas.
2009-01-16, 10:57 AM
It is interesting that you all understand the DOC has protected a bunch of freqs for OTA stations that are not likely to be built. I refer to that as the canadian RF defense shield. It is a shield of paperwork designed to protect canadians from recieving american programming. I believe it explains a lot of the trouble you are having getting some of our signals. The paperwork shield uses the power of litigation to insure protection for those of you north of the border that need to be protected from recieving what you want to recieve.
2009-01-16, 11:14 AM
By way of introduction, FraserR is a broadcast technician from WCAX who generously contributes regularly to the Montreal Station Status thread.
I'm intrigued by his viewpoint of the Canadian broadcasting regulatory system, which certainly can be both maze-like and snail-paced. Canada has a strong gut-level drive to do as much as possible to assert Canadian culture, so in facing the giant U.S. cultural onslought I think our country tries to use regulatory levers to protect itself. To me that's why things take so long and are so detail-oriented in the broadcast policy and licensing game.
I've had a suspicion that the channel allottments had deeper meaning in some ways, and people have commented here about that in the past.
2009-03-05, 03:00 PM
This thread is meant to be a more technical one, so recent posts regarding the current and future state of Canadian OTA broadcasting have been moved into their own thread:
2009-03-05, 07:26 PM
It is interesting that you all understand the DOC has protected a bunch of freqs for OTA stations that are not likely to be built.Why would the DOC "reserve" station on behalf of the CRTC? The CRTC is responsible for ensuring cancon rules are enforced and respected as well as access to "foreign" programming restricted. The DOC along with Industry Canada allocates the channel frequencies based on radiation footprint and interference patterns with other channels in cooperation with the FCC along border areas. Are you saying that there is collusion between government agencies to restrict access to some of the American channels along border regions?
2009-03-05, 10:47 PM
The DOC along with Industry Canada
AFAIK, DOC == Industry Canada. I think the DOC refers to the former Department of Communications, which is now part of the Depertment of Industry (Industry Canada).
Are you saying that there is collusion between government agencies to restrict access to some of the American channels along border regions?
I think FraserR probably feels that way, but its probably an artifact of protecting potential Canadian interests. Don't forget that across national borders, the number of channels to protect becomes much greater, because the borders do not occur on the natural boundaries between broadcast areas, and all of a sudden, you need to have many more signals co-existing to be able to supply 5 or 10 or 15 channels per market twice over.
2009-03-06, 12:36 PM
I think FraserR probably feels that way, but its probably an artifact of protecting potential Canadian interests.
Kind of like the way people at CBC often feel that Bell Expressview intentionally degrades CBC's HD signal to make it look worse than CTV or TSN. This likely isn't true and is likely the result of other technical issues from the signal being down converted it to 720p, but it makes a great conspiracy theory.
2009-03-24, 07:25 PM
Not sure if this is the right thread, but I'll pose the question anyway.
Why are broadcasters using 1080i as opposed to 1080p?
In this day and age, isn't interlaced video kind of.. useless?
It had it's uses in analogue, but why digital? All the digital display devices use progressive to display pictures, no more CRT's doing so)
If I'm not mistaken, the video I've recorded and processed is 60 half-frames interlaced to 30.
Why not just do 1080p30 instead of 1080i60?
720p stations send 60 progressive frames at 1280x720
Half the framerate and double the res and you're at 1080p30
Since it's a little bit over double the res, even 1080p24 is feasible.
So, are there any reasons to use interlaced over progressive? (aside from "Because we want to", of course ;))