# Homemade OTA antennae?



## whitey809 (Jan 30, 2006)

Was fiddling around my attic in the house I've lived in about a year, and discovered the previous owner had at one time constructed a TV antennae using wire connected to terminals. It's a four sided antennae, each side running about 10 feet. I'm wondering if this could be used to pick up OTA HD signals. I'm pretty close to the antennae cluster in L.A. County (91001 zip). Using a silver sensor in the attic, I get CBS and ABC pretty reliably, and everything else sketchy, with Fox not at all. Does this seem worth the effort (would just have to buy a new attachment for the coax cable)? Thanks in advance.


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## dswallow (Dec 3, 2000)

You can try, though it doesn't sound like a configuration I've heard of before; it might have been used for some purpose other than VHF/UHF television.

It'll either work or not. No harm should come for trying. Odds are if a silver sensor isn't working well for you and if you're close to the transmitters, you probably need something rather directional that can reject reflected signals well, so I wouldn't hold my breath that what's up there is going to be an improvement. You'd probably be better off trying some commercial antennas that are very directional.


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## JimSpence (Sep 19, 2001)

That antenna was most likely used to improve AM radio reception. But, if you are close enough to the towers it could work. Some people use coat hangers.


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## captain_video (Mar 1, 2002)

Don't forget to don your tinfoil hat before firing it up!


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## dswallow (Dec 3, 2000)

JimSpence said:


> That antenna was most likely used to improve AM radio reception. But, if you are close enough to the towers it could work. Some people use coat hangers.


Except his silver sensor isn't doing well in the attic.

Also note that 99% of the signal is blocked by the average attic. I'd be curious to know how well the silver sensor does outside the attic.


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## Andy in NYC (Apr 3, 2002)

I'm not sure how accurate that 99% number is.

We live in NJ and just had our roof reshingled (whether that is meaningful or not isn't something I can attest to, but it is information). My guy put my antenna (a Winegard 9095 and a pre-amp) suspended by wire in my attic. I receive all the Philly stations (pointed the other direction would get me the NY stations) perfectly. Saves the WAF of a 10' mast above the house with a big Christmas Tree as well as the weathering effect of having it outside.

I'm using a Leviton 47692-GSM (1x8 2GHz Distribution Module) to feed the splits to various locations around the house. The Leviton's power is tuned all the way down or I'd overload the HR10-250 with the signal.

Given that I can avoid combining signals and then resplitting them, I like using separate feeds for each line (although the outlet behind the TV now has far too many lines coming out - 2 x sat, 1 cable, 1 OTA, 1 phone, 1 net, and lines going IN to the sub and sat speakers. Good Grief. lol.

Andy


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## dswallow (Dec 3, 2000)

Andy in NYC said:


> I'm not sure how accurate that 99% number is.
> 
> We live in NJ and just had our roof reshingled (whether that is meaningful or not isn't something I can attest to, but it is information). My guy put my antenna (a Winegard 9095 and a pre-amp) suspended by wire in my attic. I receive all the Philly stations (pointed the other direction would get me the NY stations) perfectly. Saves the WAF of a 10' mast above the house with a big Christmas Tree as well as the weathering effect of having it outside.
> 
> ...


The 99% number is based on actual measurements a television engineer has made from numerous actual attics of differing construction and outside those same homes with the same antennas.

Signal level doesn't matter that much as long as the signal level is a minimum threshold above the noise level.


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## newsposter (Aug 18, 2002)

dswallow said:


> Except his silver sensor isn't doing well in the attic.
> 
> Also note that 99% of the signal is blocked by the average attic. I'd be curious to know how well the silver sensor does outside the attic.


Sorry but I have to correct another 90% statement (other thread also)  Ok maybe you saved yourself by saying 'average' but i'd expect a more accurate and detailed statement from someone with more knowledge  No way is *99%* of the signal blocked unless you have some seriously reflective stuff on the roof. If that is 'average' in America, well I truly dont know that. People that have homes with just wood/shingles, can get a significant signal through just fine.

40 miles from the towers, from my attic mount, I was getting 2 low UHFs on the HDtivo with 90s signals and even upper UHF (ch 64/67) at a signal of 70ish to 85 ish. It was 2 lower powered mid ranges that were tough for me.

For comparison, even outside, the high UHF did not improve beyond the 85 i had as my indoor maximum. But what it did do, is help stablize the signal so yes, i was losing something, but nothing near 99% of the signal.


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## dswallow (Dec 3, 2000)

newsposter said:


> Sorry but I have to correct another 90% statement (other thread also)  Ok maybe you saved yourself by saying 'average' but i'd expect a more accurate and detailed statement from someone with more knowledge  No way is *99%* of the signal blocked unless you have some seriously reflective stuff on the roof. If that is 'average' in America, well I truly dont know that. People that have homes with just wood/shingles, can get a significant signal through just fine.
> 
> 40 miles from the towers, from my attic mount, I was getting 2 low UHFs on the HDtivo with 90s signals and even upper UHF (ch 64/67) at a signal of 70ish to 85 ish. It was 2 lower powered mid ranges that were tough for me.
> 
> For comparison, even outside, the high UHF did not improve beyond the 85 i had as my indoor maximum. But what it did do, is help stablize the signal so yes, i was losing something, but nothing near 99% of the signal.


I'm talking 99% of the signal energy. That has nothing to do at all with the "signal level" readings you see on your receiver; that represents an error correction usage rate showing whether or not the signal is being decoded well.

Here's a post from the guy who actually has made the measurements; Somewhere he's probably talked about it more specifically but last year he sent me some of his raw data graphed -- 20db loss is typical; that means 1% of the signal is making it to an antenna in your attic versus what would get there if the antenna were outside and unobstructed.

http://www.avsforum.com/avs-vb/showthread.php?p=6307937&&#post6307937


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## newsposter (Aug 18, 2002)

dswallow said:


> I'm talking 99% of the signal energy. That has nothing to do at all with the "signal level" readings you see on your receiver; that represents an error correction usage rate showing whether or not the signal is being decoded well.


I had no idea. Wonder where i can get more detail on what this meter is telling me. they really shouldn't label it as a signal meter if that's what it's not!

So i was only getting 1 percent energy in and got that good a pic. Wild..wonder why they dont just cut the signal down since for outside antennas you dont need that much


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## whitey809 (Jan 30, 2006)

I'll try it out anyway, and let you guys know how it turned out. Thanks for the input.


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## Stanley Rohner (Jan 18, 2004)

It's all your fault if martians invade earth the day after you hook up that contraption.


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## wje (Jan 8, 2005)

The antenna design sounds like what's called a rhomboid. With the dimensions you gave, it's not appropriate for the UHF signal range used for digital TV... it's a low-frequency antenna for AM radio. While you might pick up something, it sure won't be anywhere near optimal. If you're in a fringe area, you really should go for a high-gain antenna designed for UHF.


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## TheBigDogs (Oct 14, 2004)

I gotta tell you guys, you really brought back the memories. 

When I was a kid, I'd spend my summers with my uncle who ran a dairy farm with grapes, almonds, chickens and pigs. A new radio station came into town, Chico, and the milk production dropped. My uncle called them to turn off their radio station because the electric waves were messing up his milk production. 

Well, they didn't respond so he took some bailing wire and we spread it on the ground and measured meticulously. Once we got the right length, he wrapped the wire around the pig sty and connected a 100 watt bulb to the two ends of the wire. The bulb lit and kept the sty lit 24/7 for the remainder of the summer. 

When I returned the following summer there was no light (the wire remained). I asked about the light and got told that the "damn government made me take it down". 

So, ******, be ready for the "damn government" to pay a visit when you hook that thing up. 

....and, good luck!


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## TyroneShoes (Sep 6, 2004)

wje said:


> The antenna design sounds like what's called a rhomboid. With the dimensions you gave, it's not appropriate for the UHF signal range used for digital TV... it's a low-frequency antenna for AM radio. While you might pick up something, it sure won't be anywhere near optimal. If you're in a fringe area, you really should go for a high-gain antenna designed for UHF.


That's what I thought, too. Rhomboids were also used for DX-ing distant TV stations, but if I remember correctly they were pretty frequency-specific, and not very directional, even though they had a lot of gain. Probably not a good choice for ATSC, especially when a 4228 can be had for $39.


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## Runch Machine (Feb 7, 2002)

dswallow said:


> Except his silver sensor isn't doing well in the attic.
> 
> Also note that 99% of the signal is blocked by the average attic. I'd be curious to know how well the silver sensor does outside the attic.


I don't know where this 99% figure comes from but it's way off. I have a field strength meter and measured signal level from a 4221 on the roof and then in the attic. Raw signal strength delined by a little less than half. I still have more than enough to split it and feed 3 receivers, including an HD Tivo. I am 16 miles from the transmitters and live in a one story rambler.


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## TyroneShoes (Sep 6, 2004)

By "half", I'm assuming you mean about 3 dB? If so, you are correct. The signal would have to drop by 20 dB to be 1/100th of the original strength. Not too many received TV signals, ATSC or NTSC, could tolerate 20 dB of loss, so the preponderance of successful attic installs over the last 5 decades makes me think the "study" is flawed.

A 20 dB loss sounds about right for an attic that has metalized film insulation bats or metal screen under stucco, or the equivalent, and a 3 dB loss sounds about right for an attic without either of those little problems, so maybe a better "study" would include delving into the construction materials rather than just trying a bunch of different attics blindly in serial fashion. Odds are against it, but maybe the "study" was done in a neighborhood using the same construction techniques in all attics tested. Bottom line, it doesn't appear to be very empirically sound.


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## Runch Machine (Feb 7, 2002)

You are of course, right when you say the attic construction material makes a HUGE difference. Mine home is made of wood with asphalt shinges. No metal is used which could cause reception issues. I like the reliability of over the air reception. No matter how hard it storms, I can always pickup our local digital stations and see what is going on.


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## TyroneShoes (Sep 6, 2004)

Oh my God.

I just reread the "source" of the study. Not only did the guy only do 3 attics, he mentioned 15-20 dB, not "99%". While 20 dB of loss would be equivalent to 1/100th, 15 dB would be more like a loss of about 65% of the signal, so the truth probably lies somewhere in between for his little non-scientific sample. Not only that, but by the name and location, I think I know this guy, and if I do he's one of the more "clueless" fellow broadcast engineers I've had the "pleasure" to know or work with (1983-90) in the last 30 years. And I'm honestly trying to be nice, not cruel, when I say this.

Much of what he says is true, however. But that sweeping generality about vertical directivity? Huh-uh. Typical arrogance of that guy. The 4228's polar plots look very similar in both H and V axes, as do those of many other antennae. And tilting a directional antenna and noting the drop-off is hardly any indication of its vertical directivity when you aren't in free space but are traversing normal (or abnormal) terrain. Also highly unscientific, and also typical of this guy's fuzzy thinking processes.


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## newsposter (Aug 18, 2002)

nice to see i'm not the only one that thought the 99% was a tad off


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## dswallow (Dec 3, 2000)

Anecdotal conversations are always fun; now let's see your real data.

http://www.2150.com/files/20041211_attic_antennas_v03.pdf


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## dswallow (Dec 3, 2000)

TyroneShoes said:


> Oh my God.
> 
> I just reread the "source" of the study. Not only did the guy only do 3 attics, he mentioned 15-20 dB, not "99%". While 20 dB of loss would be equivalent to 1/100th, 15 dB would be more like a loss of about 65% of the signal, so the truth probably lies somewhere in between for his little non-scientific sample. Not only that, but by the name and location, I think I know this guy, and if I do he's one of the more "clueless" fellow broadcast engineers I've had the "pleasure" to know or work with (1983-90) in the last 30 years. And I'm honestly trying to be nice, not cruel, when I say this.
> 
> Much of what he says is true, however. But that sweeping generality about vertical directivity? Huh-uh. Typical arrogance of that guy. The 4228's polar plots look very similar in both H and V axes, as do those of many other antennae. And tilting a directional antenna and noting the drop-off is hardly any indication of its vertical directivity when you aren't in free space but are traversing normal (or abnormal) terrain. Also highly unscientific, and also typical of this guy's fuzzy thinking processes.


Your "clueless fellow broadcast engineer" at least has a grasp on a 15db loss being 3.125% of the signal.


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## whitey809 (Jan 30, 2006)

No dice. I hooked up the infernal contraption this weekend. Only got one digital channel (foreign language). Must have indeed been an AM antennae. No aliens or government spooks have dropped by...yet.


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## newsposter (Aug 18, 2002)

If possible, i'm sure we'd love to see a pic of it


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## TyroneShoes (Sep 6, 2004)

All of this concentration on what per cent of the signal remains after attenuation by an attic is leading us to focus on the wrong thing, which is the difference in how large the signal is compared to how large it is after passing through an attic. While a loss of 99% sounds like a lot, you have to put that into perspective before it can really mean anything.

The difference between what is radiated from a transmit antenna in any particular dimension as measured from very close to the antenna and what is received by the first receiving antenna the closest to it is also hugely different, and significantly more than an attenuation of 99%. The first number (EIRP) may be as much as 5 megawatts (less of course in a particular direction), and the second number (based on the current induced into your tuner front end from your receive antenna) is in the microwatts. That's up to 11-12 orders of magnitude of free space attenuation, which makes an attenutation of 99% of the signal by an attic seem pretty infinitesimal by comparison.

Here is the important thing. It's not how much signal is lost from point A to point B, it's whether you have enough remaining to stay +15 dB over the noise threshold. Period. If the signal is at least 35 dB above the noise threshold as it reaches your attic, losing 99% of the power would not matter one bit, because you would still be above that critical point once the signal reaches your tuner. In short, that kind of loss just doesn't matter if you have enough signal to begin with. Folks close to strong transmit towers might be able to tolerate that kind of a loss, and folks far from weaker transmit towers might not. That's important. What percent of the power is attenuated really isn't.

The signal received from DTV is attenuated -200 dB from its strength as it is transmitted from the satellite. You math whizzes out there must realize that this is but a tiny fraction of a percent of the power remaining, much, much tinier than what a 20 dB attenuation from an attic might be. But that comparitively huge power loss is just not a problem. Being 65 miles from a terrestrial transmit tower might be a handicap, yet being 23,000 miles away from the satellite just never is. As a matter of fact, the entire amount of power of every received satellite signal that ever reached a receiving dish on earth since the first sat transmission in 1957 _combined together_ is still less than the force of a single snowflake hitting the ground. Now that's a lot of transmitted power, and not so much received. That's real attenuation.

Reception is not really about power and what percentage of it might be attenuated. It's instead all about and only about having enough power at the front end of the tuner to remain comfortably above the noise floor. Concentrating on the former is a roundabout way of attending to the latter, and can end up obscuring the real goal. A loss of 99% of the signal sounds significant. It can be. But it can also not be, even when limited to the effect of an attic on OTA DT.

Bottom line, if you are far from the towers it makes common sense to realize that you might have to do everything you can to maximize reception, including not installing the antenna in an attic, as well as using a directional antenna and mounting it as high as possible. If you are fairly close, an attic install might be just fine, and one attic might have a quite different effect than the next, depending upon its construction. That makes the sensible advice to just forget about the attenuation percentages and the abstract numbers surrounding and confusing the issue, and to rely on common sense instead.


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## newsposter (Aug 18, 2002)

TyroneShoes said:


> As a matter of fact, the entire amount of power of every received satellite signal that ever reached a receiving dish on earth since the first sat transmission in 1957 _combined together_ is still less than the force of a single snowflake hitting the ground. Now that's a lot of transmitted power, and not so much received. That's real attenuation.


What's the standard measurement for

a. power of every signal that reaches earth
b. force of a single snowflake


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