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Author Topic: Metal roof on our house a problem for OTA antenna?  (Read 950 times)
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sliderule
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« on: December 11, 2017, 12:15:33 AM »

Currently using sat TV and am considering getting an OTA antenna.  We have a large house with a metal roof.  I don't need to be aiming through the roof and won't need to mount an antenna higher to see over the roof.  But if the antenna is aimed away from the roof, will the large expanse of sheet metal interfere with reception?  I use a portable AM/FM radio around the house & garage sometimes and the roof really messes up FM reception.  Roof is not grounded of course (and can't be), if that would make any difference.

I have a tower at one end of the house for a shortwave radio antenna and the top is above the highest point on the roof.  *If* it would really, really improve things, I could mount the antenna on it but would be a major job and would have to lower the mast to the ground.
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Gil
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« Reply #1 on: December 11, 2017, 12:21:48 AM »

If we still had analog tv, you might get some 'ghosting', but with digital tv, I am not sure what to expect. Hopefully your ota antenna has enough front to back ratio to reject any signals that might be present. I have to wonder if the digital tv is like FM signals where the strongest one by 6 db captures the receiver. JMHO   Viejo
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E_V
The old tomcat sat on the backyard fence, his feet were full of blisters; his head was up and his tail was down, and the wind blew through his whiskers.
Xubuntu 14.04.5 LTS AMD64 ASUS M4A7XTD EVO
True FTA: DMSI Hotdish90 (37") for 91W, 97W and 103W; Samsung JS851C11 (33") for 123W ITC; DN pro plus for 118 ITC & 125W; Winegard DS3101 1Meter 103W, Prodelin 1.2m for 99W-C.    All going to a Amiko Nano HD, an OpenBox S9, and Linkbox 9000i Local.
sliderule
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« Reply #2 on: December 11, 2017, 03:10:01 AM »

If we still had analog tv, you might get some 'ghosting', but with digital tv, I am not sure what to expect. Hopefully your ota antenna has enough front to back ratio to reject any signals that might be present. I have to wonder if the digital tv is like FM signals where the strongest one by 6 db captures the receiver. JMHO   Viejo

Haven't chosen an antenna yet.  Looking around at Channelmaster, Wineguard and others, there's such a bewildering number of them in all sorts of shapes, sizes and performance claims...   
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Gil
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mopat
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« Reply #3 on: December 11, 2017, 09:02:31 AM »


There are a lot of unknowns with your questions.  Could you post your tvfool report?

What does this mean "won't need to mount an antenna higher to see over the roof"?
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WS9036 dish, Spitfire Lnb, Powermax SG9120 rotor, .
10' solid dish with C1-PLL, TBS6982 card running SmartDVB
sliderule
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« Reply #4 on: December 11, 2017, 12:26:41 PM »


There are a lot of unknowns with your questions.  Could you post your tvfool report?

What does this mean "won't need to mount an antenna higher to see over the roof"?

The highest peak of our roof is something like 30' above the ground but looking at TVfool, I won't have to aim in a direction that would require the antenna to be above the peak (to clear the sheet metal).  Antenna would be on the west side of the house and be in line of sight to the available stations in a westerly and south-westerly direction.

TVFool report:

Code:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d60ed46cba743c3

The rear of the main house portion faces west as in this photo and the garage portion (has the lower roof) is turned 22 degrees.  An antenna at either the north side of the house or south side of the garage would be best for getting coax into the house where the receiver would be.

« Last Edit: December 11, 2017, 08:19:52 PM by Hyper » Logged

Gil
Langley, BC
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« Reply #5 on: December 11, 2017, 08:22:11 PM »

Wow, nice place you have there sliderule. And this is an excellent question, one i have never thought of before. And i am planning on getting a metal roof next time i have to replace my roof. I actually have no idea if that will affect reception from an OTA antenna. Hopefully somebody who knows can chime in here.
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Hyper
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« Reply #6 on: December 11, 2017, 08:25:56 PM »

Based on your TV Fool Report, i think for an outside antenna the RCA ANT-571 would be a decent choice for an outdoor antenna.

Check out this thread for that antenna, plus a few others that forum members have tested:

http://legalfreetoair.com/index.php?topic=33807.0

For an indoor attic antenna check out this one:

http://legalfreetoair.com/index.php?topic=47819.0

Both these will work well in the 40 mile range

If you need to get those channels 70+ miles out you will need a big deep fringe antenna, and those are expensive!
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My son Evan, taken from his family and friends on March 26, 2010 at the age of 15. We love you and miss you Evan. We will see you again soon in heaven. I miss you son. You were the best son a dad could have. I am so proud of you. Save a place for me.
elbandido
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« Reply #7 on: December 11, 2017, 10:28:38 PM »

Start looking and you will find many examples of television antennas, and other types of antennas on top of or near metal roofs. The metal may actually help the signal somewhat, depending on several conditions, but at the worst case, the antenna will see the metal as ground. Personally, I would not spend time worrying about the metal. I would worry more about the height above ground and size of the antenna.

VHF tv signals seem to work pretty good starting at around 7 wavelengths above ground, or around 14 wavelengths above ground for UHF.  Bigger is better for television antennas, especially in rural areas.  A Good rotor also helps, or at least use- multiple antennas for different directions. Some people combine the signals from two antennas which is a compromise. I use enigma2 receiver with multiple atsc tuners that allows me to seamlessly switch between two ota antennas without the loss of combing them.

Attached is a picture of the tv antennas that I normally use. On a given day, I can usually get between 80-90 OTA channels. This sounds like a lot, but one frequency may have many sub channels. Being near a big city such as Atlanta helps too.
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El_Viejo
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« Reply #8 on: December 12, 2017, 09:36:15 AM »

Don't think he should consider an attic antenna because the metal roof would block most if not all signals.  JMHO  Viejo
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E_V
The old tomcat sat on the backyard fence, his feet were full of blisters; his head was up and his tail was down, and the wind blew through his whiskers.
Xubuntu 14.04.5 LTS AMD64 ASUS M4A7XTD EVO
True FTA: DMSI Hotdish90 (37") for 91W, 97W and 103W; Samsung JS851C11 (33") for 123W ITC; DN pro plus for 118 ITC & 125W; Winegard DS3101 1Meter 103W, Prodelin 1.2m for 99W-C.    All going to a Amiko Nano HD, an OpenBox S9, and Linkbox 9000i Local.
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« Reply #9 on: December 12, 2017, 10:27:57 AM »


Thanks for your tvfool report.  Your reception should be pretty good.

You should be able to receive those listed down to channel 39 with a NM of -2 dB.

Your beam-width situation is also not bad, promising.
The majority of stations between 325 and 281 degrees for a desired beam-width of 44 degrees.

All of your stations are in the UHF band except channel 3 the GTN network; I would not bother trying to receive this.
Your antenna choice would only need UHF not high-band VHF, making the antenna smaller and more manageable.

With the distances involved and the desired beam-width I would avoid antennas of a Yagi design and focus on those with a bow-tie design.

A 4-bay bow-tie antenna pointed about 290 degrees magnetic should do the trick;  I would use a pre-amp mounted on the antenna mast, something like a RCA TVPRAMP1R .
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elbandido
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« Reply #10 on: December 12, 2017, 12:20:46 PM »

It might be a good idea to check and see if any of the UHF tv channels are moving to VHF for the repack?


A bow tie antenna probably has advantages over a yagi when a lot of ground clutter is involved, but a good yagi at a reasonable height is hard to beat! Yagi type designs are the main choice of cable operators. You see few if any bow tie type antennas on cable towers.
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mopat
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« Reply #11 on: December 12, 2017, 12:34:35 PM »


Just thinking Yagi beam-width is narrower, this situation 44 degrees of beam-width would be nice.
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WS9036 dish, Spitfire Lnb, Powermax SG9120 rotor, .
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« Reply #12 on: December 12, 2017, 01:27:45 PM »

Good point about the channel changing due to repack, bandido!!!!   Viejo
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E_V
The old tomcat sat on the backyard fence, his feet were full of blisters; his head was up and his tail was down, and the wind blew through his whiskers.
Xubuntu 14.04.5 LTS AMD64 ASUS M4A7XTD EVO
True FTA: DMSI Hotdish90 (37") for 91W, 97W and 103W; Samsung JS851C11 (33") for 123W ITC; DN pro plus for 118 ITC & 125W; Winegard DS3101 1Meter 103W, Prodelin 1.2m for 99W-C.    All going to a Amiko Nano HD, an OpenBox S9, and Linkbox 9000i Local.
DAVE5
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« Reply #13 on: December 12, 2017, 08:02:18 PM »

If you mount the antenna on or near the metal roof like an eve mount you are required by NEC code to ground the TV antenna bounded to the electrical service.  WHY???  You will have a feedline going into the house and and when your antenna gets hit by lightning the bolt  of lighting will come into the house and will start a fire. You will also have to install a lighting arrestor when the feedline penatrates the wall.   This includes any antenna on your grounded tower.   There nothing wrong having a complete lightning protection system on a metal roof with lightning rods.  Many 200 year old barns and all commercial building have metal roofs have lightning rods and they are required by NEC code for fire prevention.  Even with proper lightning protection systems on the antenna does not mean it will keep from having lightning damage to TV tuner or even a satellite receiver. If you get a direct hit you most likely have first Field Effect or LNB HEMT front end damage as the gate is less than a micron thick and it does not take much static electricity to puncture and destroy the  gate of the semiconductor.   There is a upside you will not burn down the house if you do get a lightning  strike.  Also you wont have to file a claim with the insurance company as they will pro rate everything to a very low rate and will not get full value of the contents.

Lightning protection is cheap insurance.

DAVE5
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sliderule
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« Reply #14 on: December 13, 2017, 01:55:59 PM »

Thx for all the comments!

Attached is a photo of the tower against the north side of the house and is about 35' tall.  It's just begging to have an antenna sitting on top.  I am going to think about that.  I hoisted it up using a come-along and was a slow process.  A few years ago there used to be a guy that advertised on Craigslist that he was available to climb antenna towers, but even if a person was available, I don't think it would be fun hoisting an antenna, rotor and a few other things up to the top and imagine it would be expensive.

I'm leaning towards a yagi type and if I put it atop the tower along with a rotor, I'm thinking it would be as good as I can get.

Interesting point from DAVE5 on grounding and lightning and thanks for bringing that up.  The two towers I have are each grounded at the base with a couple of rods.  We rarely get lightning around here and when we do it's usually sheet lightning.  You don't see lightning rods on houses around this part of Canada which is where I am (southwest corner of BC).  Not sure what the current regs are for lightning protection and will have to look into it.  Our metal roof is a "standing seam" type with interlocking 12" wide panels running in a vertical direction.  Panels have a painted coating and are electrically isolated from each other.   It might be better if all 12" lengths were bonded together but not feasible.  Just bought a new FTA receiver (Geosatpro) and I certainly don't want that to ever get fried.

I'm an EE (retired).  I once did a lightning protection system for Dept. of National Defense.  It was a small solid rock island and I ran heavy bare copper cables in a grid pattern and had a bunch of plate electrodes in the ocean.  Had to hire a couple of divers to inspect the plates.  One of the most interesting and challenging projects I did.   I studied radio wave propagation in school way back in the 70s but probably forgot it all shortly after.  Computers and electronic stuff isn't my thing either so have lots to learn when it comes to satellite & FTA TV and OTA TV.  About to put up a 36" dish for KU FTA TV and have a line on a 10' BUD but it's long way from home and have to work out logistics of getting it here.  I'm going all in on this stuff!  Got interested in sat & OTA TV from having an RV and started using sat TV a couple of seasons ago and have been playing around with LNBs, dishes, tripods, etc.

Wow, nice place you have there sliderule.
  Thanks.  I had someone do the framing, concrete, roof & drywall and I did the rest.  Has only taken 14 years so far, lol.  Pretty much done now and just a few minor things left to do.  Never building another one at my age - time to focus on some hobbies...

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Gil
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