Monday, 12 May 2008

In Passing

Question for the engineers


Stumbled across this while searching for recommendations for a CECB:

Don Bouldrey: Since I’m still dumb as a stick about this dtv, I've assumed [component over-] heating has been causing signal dropouts but now it appears as though it’s the wind causing that on the weaker stations. I use folded dipoles of different wavelengths hung in a cedar tree to pull from transmitters that are in three different directions and spread by 50°. Hey, it works fine for analog, even in a hurricane, but I’m learning digital is a different animal.

bdfox18doe (Charlotte, NC): You’re encountering dynamic multipath that the receiver isn’t fast enough to correct for. Nearby trees, especially when wet, will really affect ATSC reception, especially at UHF frequencies. And some receivers handle it much better than others.

Don Bouldrey: I can see that I’ll be rethinking my old antenna system. Even though my dipoles are tuned to frequency and aimed at the towers, this wind issue will be a pain. Otherwise, everything is about as good as it can get. Funny thing with the ATSC is the propaganda is really exploiting the safety and reliability of DTV and discussing the value of it for keeping people safe in emergency.... while showing footage of a hurricane in action. Like you, I'm thinking ATSC will be useless in a hurricane whereas the analog TV works just fine no matter what the conditions. When ’cane Ivan hit us @ 135, every time I saw the red doppler bands heading for our house, all hell broke loose. Our reception remained perfect all night long. I should say it was perfect for the one station that managed to stay on the air throughout the night.

I wonder if there's any contingency plan for reverting to analog when hurricanes are heading in. An inoperative television system just won’t fly in hurricane country.

Scooper (Youngsville, NC): I'd like to hear from some members in hurricane country right after a ’cane goes through to get the straight scoop on this. I've noticed that my reception is rather spotty with blowing, wet trees, but that is exactly what I attributed it to - blowing, wet trees. It doesn't do DBS any good either.

satpro (central FL): ATSC works fine in a hurricane, tested during trifecta hurricane season a few years ago during Charley, Francis and Jeanne in Orlando. What doesn’t work is when the stations don’t bother to have a generator with gas in it hooked up to the DTV transmitter or the cheap %^&&*(# choose to shut the DTV off to conserve fuel, shutting down distant cable companies who take the DTV feed.
What about it, engineers?  What can we expect re: digital television reliability under adverse conditions?

Posted by: Old Grouch in In Passing at 17:30:31 GMT | Comments (6) | Add Comment
Post contains 453 words, total size 4 kb.

1 I am not an engineer, nor do I play one on television, nor did I spend the previous night in a Holiday Inn Express, but DTV around here holds up pretty darn well in severe thunderstorms and/or tornadoes, at least at close range.   Then again, almost all of our towers are on an antenna farm to the northeast of the city: you point in their general direction, and you get 'em.   I'd be a little more leery were I 40 miles away instead of 9, especially since all our current DTV is UHF.  (After the switch, two stations will revert to their VHF channels, and a third will move to a different one.)

Posted by: CGHill at 05/13/08 02:57:15 (g/E2o)

2 Multipath does affect 8-VSB DTV badly, especially when it changes rapidly.   For instance, if you're using any antenna with poor front-to-back ratio in a hurricaine.  Simple dipoles and rabbit ears are among the worst that way.  At UHF, you can add a close reflector on the side away from the stations and it will help a lot -- VHF, not so much, as it has to be larger.  (Foil on cardboard, bend into a shallow V and stand it up behind the antenna). Outdoor Yagis work much better...of course, in a hurricane, they've got a lot of windloading.  An attic Yagi might be a better choice, along with (if possible) prompt evacuation ahead of the storm. No amount of TV will make you safer if the thing visits you.

Posted by: Roberta X at 05/13/08 19:43:08 (pGthN)

3 <em>"No amount of TV will make you safer if the thing visits you."</em>

That's for sure.  I noticed that almost all the DTV assignments are for either high-band VHF (7-13) or UHF (14-51); channels 2 through 6 are being mostly abandoned.  Could the multipath issues be worse on the longer wavelengths?

Posted by: CGHill at 05/15/08 01:05:30 (g/E2o)

4 Hmm.  That's what I get for assuming every editor speaks the same dialect of Tag.

Posted by: CGHill at 05/15/08 01:06:53 (g/E2o)

5 Test.

Hmmm, again.

The comment editor is the one screwy thing around mee.nu. I don't even see it when I post comments-- appears that the javascript widget doesn't like K-Meleon. Instead I get a raw entry box in which even linebreaks have to be coded. (The WYSIWYG one for posts works fine... go figure!)

Posted by: Old Grouch at 05/15/08 01:42:58 (c5WZW)

6 I'd fix yours, but it only allows me to delete comments, not edit them.

Posted by: Old Grouch at 05/15/08 01:47:35 (c5WZW)

Hide Comments | Add Comment

Comments are disabled. Post is locked.
73kb generated in CPU 0.0145, elapsed 0.4226 seconds.
53 queries taking 0.413 seconds, 214 records returned.
Powered by Minx 1.1.6c-pink.