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Attenuation of roofing material


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6 replies to this topic

#1 OFFLINE   chrisk

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Posted 07 June 2004 - 04:19 PM

I live in a two story wood frame house with an asphalt roof. I am planning on putting an antenna for HDTV in my atttic. Any info on the signal loss due to the asphalt shingle roof? I am about 40 mi. away from Raleigh, NC according to www.antennaweb.org. The stations there broadcast in the 900 - 1000 KW range. I am looking at an antenna from www.hdtvantennas.net that have a gain of around 14DBi and using a pre-amp. Any thoughts on my chances of receivning HDTV broadcasts with my Dish 811 receiver.?

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#2 OFFLINE   RJS1111111

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Posted 09 June 2004 - 10:58 AM

I live in a two story wood frame house with an asphalt roof. I am planning on putting an antenna for HDTV in my atttic. Any info on the signal loss due to the asphalt shingle roof? I am about 40 mi. away from Raleigh, NC according to www.antennaweb.org. The stations there broadcast in the 900 - 1000 KW range. I am looking at an antenna from www.hdtvantennas.com that have a gain of around 14DBi and using a pre-amp. Any thoughts on my chances of receivning HDTV broadcasts with my Dish 811 receiver.?


Assuming the HD broadcasts are on UHF channels (based on the Mega-Watt ERP levels), attenuation through the roof might possibly get slightly worse in wet weather. Other than that, I'd say your chances are very good, if you've got a line-of-sight incoming signal without too much multipath reception. Line of sight requires considerable altitude 40 miles away; for either the transmitting or receiving antenna or both. Multipath is usually caused by signal bouncing off nearby tall buildings.

#3 OFFLINE   red hazard

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Posted 11 June 2004 - 01:41 PM

Two articles I've read on the subject indicate about a 50% (-3db) signal loss through a typical roof (plywood + asphalt shingles). Of course that is approximate loss since not all houses have the same slope.

#4 OFFLINE   chrisk

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Posted 26 June 2004 - 12:25 PM

This install started as a question on www.dbstalk.com about the attenuation of roofing material. My research indicated I would loose about half the signal (3db) going through the roof versus outdoor mounting. The Chief Decorating Officer (my wife) really did not want an antenna on the roof nor did I. I began by researching the available stations on www.antennaweb.org. This site showed that I would need a “Blue” antenna to get all the stations. I am located in Fayetteville, NC and antennaweb showed six stations broadcasting DTV out of Raleigh, NC. The longest distance was listed at 41 miles on an azimuth of 36 degrees. My house faces north and is located on a hill. The view of the nothern horizon is ok but there are a few pine trees about 125 yards away that partially obscure the horizon. I looked at a topographic map for the area and I did not see any mountains or large hills between my house and the towers. I also read about over the air (OTA) antenna installations on www.avsforum.com , www.remotecentral.com and www.hdtvpub.com. Most indications were that the roof would cause 3db attenuation however one post on avsforum said basically the roofing material was transparent to UHF but it is the water on the roof during rain storms and trapped between the shingles and the moisture barrier that would cause signal loss.

Most sites spoke very highly of the Channel Master 4228 8-bay bow tie antenna. This antenna has excellent gain and a fairly flat gain curve at the UHF frequencies I was interested in receiving. I found a gain plot on www.hdtvprimer.com for the 4228 and it indicated a peak at about 14dbd. I also looked at the www.antennasdirect.net DB-8 which the manufacturer rates at 15.8 db gain. Figuring I needed the most gain since I was planning an attic installation, I purchased the $99 DB-8. While this was more expensive than the $49 CM 4228, antennasdirect offers a 90 money back guarantee. If the antenna did not pull in the signals I could return it and only be out shipping. All the vendors for the CM 4228 I could find on the net did not accept returns for installed antennas so I would be out shipping plus the cost of the antenna if it did not work.

I received the DB-8 on 23 June and I was planning the install for the coming weekend. Just for kicks, I assembled the antenna and placed it a front room on the first floor of my house on the floor. The lower half of the antenna was behind the wall and the upper half was behind a window. A large bush was in front of the window and the antenna was pointed due north versus at 36 degrees. I hooked it up to my Dish 811 receiver with 50 feet of RG6. When I scanned for digital channels I was surprised to see I received eight DTV signals. When I checked the signal strength I found six of them were in the 70% range, one in the 60% range and one with the dreaded 811 49% reading. The one at 60% would not lock in so the picture was not usable. I now felt much better about the attic install coming up this weekend.

Early Saturday morning I installed a CM 1.25 inch mast with a swivel mount hung from a rafter in the attic. I attached the DB-8 to this mast and pointed the antenna at 36 degrees azimuth using a Walrmet compass. I already had an unused RG-6 CATV run from the attic down to the crawl space so I terminated the cable run and attached it to the antenna with no preamp. In the crawl space I had to attach another length of RG-6 to the run from the attic and pull this through the floor and wall to the box behind the TV. From there I used a 6 foot jumper to the Dish 811. When I scanned for digital channels I was able to receive ten channels. Eight of them have signal strength in the 80% - 90% range, one is in the 62% range and one has the dreaded 811 49% reading. I tried moving the antenna both azimuth and elevation wise but I could not improve reception further. It was raining quite hard when I scanned for the channels but this did not seems to affect signal strength since it is virtually the same now that the rain has stopped and the roof has dried. I plan on trying a preamp to see if I can over come the loss from the 50 feet of cable and two splices to pull in that one station that is at 62%. We'll see.

Well I tried a preamp, Channel Master 3041, from Lowes but it did not help pull in the on UPN station. I checked and it looks like is is braodcasting at 500KW while the rest of the stations are broadcasting at 900 - 1000 KW. I'll just have to watch UPN from my Dish versus over the air. Maybe I'll try one of the preamps listed in one of the responses below. Doubt it will help since the transmit power is so much less than the other stations.

#5 OFFLINE   red hazard

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Posted 27 June 2004 - 10:51 AM

From a practical point, RF signals below 7.5 Ghz are immune to rain fade. It would take extremely intense rain to affect TV signals. Possibly a hurricane could produce rain intense enough to attenuate TV signals.

The station that you are having problems with may be transmitting low power. See http://www.tvradiowo...a/usastates.asp Some of the UPN digital stations are notorious for low power.

A good preamp might help. They are not recommended if you are close to the TV transmitters. About 20 miles away or more might be OK. If all digital TV stations are UHF, suggest getting a Channel Master 7775. If some are VHF & UHF then a Channel Master
7777 is recommended.

#6 OFFLINE   Shappyss

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Posted 27 June 2004 - 12:27 PM

I live 20 miles from TV stations in NY and I used to have antenna in attic and could only recieve one out of 5 channels. I moved it onto roof and it worked much better and was able to get 100% signals on almost all channels (except for one the is on a temp. channel that is really weak. Also don't use a splitter/diplexer anywhere or a one-to-one connecter to connect two shorter cables together. When I eliminated the splits and put it on the roof my signal was much better. I also find that the biggest radio shack antenna is great, much better than what Ive heard about terk!

#7 OFFLINE   chrisk

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Posted 28 June 2004 - 05:39 PM

Red Hazard,

I think the post I read about moisture was stating that wet shingles versus rain fade could cause signal loss. Based on my observations I have not seen a problem during rain storms so I would tend to agree with you.




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