watchability - dtv vs analog

[tekha]

What's the difference in watchability between digital and analog tv? I know that analog pictures get progressively worse the further you get from the transmitter and at some point the picture becomes unwatchable. But this is a personal decision. Some people don't mind if the picture is a little snowy but some people won't watch.

Am I correct in understanding that digital tv is all-or-nothing -- you get a perfect picture or you have "no signal" message?

Thanks

[tigerbangs]

There is a gray area in digital TV reception where you can exprience macro-blocking and momentary dropouts with a less-than-good signal on a digital receiver. That occurance is usually the result of using an inadaquate antenna (indoor antennas are expecially guilty of this) or severely weak signals at the fringes of the TV signal. Many people find that the disruption of picture and sound inherent in bad digital reception is more bothersome than snow and color loss in analog. The issue is largely moot at this point because in three weeks, almost all analog broadcasting will cease and digital will be your only choice. The only analog transmitter sthat wil remain on the air will be low-powered translator stations that feed rural markets.

The upside of digital reception is that, when it is working as it should, even the standard-definition picture and sound far exceed what was available in analog broadcasting. The moral of this story is get ready to invest in a decent antenna or be prepared to subscribe to a pay-tv service.

[tekha]

I'm gearing up antenna-wise, trouble is I live in rural analog Canada close to the border and want to get the digital US stations. I live about 80 miles from those transmitters. I know this from feeding my co-ordinates into tvfool.com. My readout from them shows the digital stations I'm interested in are in a grey zone (their colour-coding) with a noise margin NM(dB) of -10 to -13. Will an antenna with amp increase the number to the point where the signal is "watchable"? And if so, what kind of antenna?

Thanks again.

[tekha]

By the way, they seem to suggest that a NM(dB) reading of 0 is sufficient to make a station watchable? What do you think?

[tigerbangs]

a 'zero noise-margin' should be an acceptable picutre 95% of the time. We can't always account for man-made obstacles or trees, so I always like a few dB more just to be sure. If you give me your Postal Code, I can tell you whether or not you have any hope of being to get the stations that you are looking for...

[tekha]

My co-ordinates are 43.09 and -80.18 and postal code is N0A 1M0.

[tigerbangs]

From your location, I would guess that you are looking for the Buffalo, NY stations. ost people in GTA an see Buffalo's digital stations, but it is going to take a very powerful antenna system to get you what you are looking for as most of the Buffalo tations are farter than 60 miles from your location. How much antenna height can you get? 30' is about average on a rooftop without using a freestanding tower, but more would help you, and I know that many Canadians erect towers to get distant TV stations. Even if you can get only 30 feet, here's what I would suggest:

Go with my deep-fringe prescription: A Wade-Delhi VIP-306SR VHF deep-fringe TV antenna plus an AntennasDirect Xg-91 UHF antenna mounted on a mast above a rotator separated by a minimum of 4'. The XG-91 should be mounted above the VIP-306SR. I am suggesting a broadband VHF antenna to you rather than a high-band yagi because Canada is going to do a lot of reassigning of their stations when they do their digital conversion, and you still have a LOT of analog stations that use channels 2-6 analog in Canada: don't rule them out for the moment. Mount the XG-91 so that it's front is tilted 15 degrees +or- from the horizon.

Use a Heavy-duty rotator like a Hy-Gain AR-40 to turn this array, as I have found that the lighter rotators like the Wade, Channel Master and Philips rotator motors are too lightweight to turn a large rig like this, particularly in the cold and snow of the Great White North...LOL

Use a high-input preamplifier like a Winegard HDP-269, since you have a LOT of local stations whose combined signal strength may overload a preamp like a Channel Master Titan 7777 or a Winegard AP-8275.

Here are some links to help you:
http://www.pctinternational.com/channel ... lation.pdf
http://www.winegard.com
http://www.antennasdirect.com
http://www.rotorsevrice.com
http://www,wade-antenna.com

[tekha]

Tigerbangs, can we nominate you for a Nobel Prize or something? You're doing such a fantastic job here. Thanks a ton.

I found your prescription for the deep fringe fix on another site from a couple years back and noticed that you recommended the CM4228 for the UHF antenna in this situation and you are now recommending the AD XG91. Just curious as to why since they look so different.

Also, the XG91 says it has a max gain of 16 and the the stations I want to reach are already at -14 -- if I can put it on a 45 foot tower. I'm thinking of not going with the VHF antenna so would I still need the heavy-duty rotor? And if I don't go with the VHF, is the Winegard HDP-269 still the best pre-amp to use? Also, would it double the Noise margin dB to something above zero?

I'm going to wait a while til the ground thaws before setting up the tower so I'll probably have a few more questions about cable splitting and the like. In the meantime, thanks again.

[tigerbangs]

If you use the XG-91 by itself, you can use a much lighter rotator. I would suggest using a Channel Master 9521a rotator, which is automatic and very easy to you. I wounder why you would want to give up VHF, though

A preamplifier cannot ever raise the digital noise margin beyond what the antenna provides, it can only compensate for line and splitting losses. If you have a signal at -14 dB Nm, and you use a 16 dbd gain antenna, then you have a net noise margin of +2 dB Nm. If you add the preamplifier to it, you have to subtract the noise lever of the preamplifier, which is 2-3dB, then subtract the line and splitting losses of your distribution system, and make sure that the preamplifier covers those losses. Even a 25dB preamplifier cannot bring you beyond 0dB Nm under these circumstances, assuming that the preamplifier has a noise figure of 2dB. If you have a preamp with a noise figure of 3dB, then the most that you can get out of the system is a Nm of -1, which may still work, but is really calling it close...