Rooftop Antenna Location
August 9, 2017 11:20 AM   Subscribe

Antenna Experts: I just upgraded our rooftop antenna, and while it's got a direct sightline to the CN Tower here in Toronto, it's mounted on the old satellite arm which is on the dormer/third floor wall of our house. I'm wondering if it's being under the overhang and so close to the wall hinders the signal in any way, and if raising it up by mounting it on the roof fascia so the antenna just clears the roof will get me more channels... or if that's not worth the hassle. Currently averaging about 25 channels.

Pictures here: 1, 2, 3.
Above the antenna is the flat roof of the third floor.
posted by chococat to Home & Garden (8 answers total)
I think we need some more context, and i am not familiar with Canadian broadcast tv.

Do you expect to receive more channels? Have you compared the channels you do receive with the ones you don't for things in common (direction, difference, antenna band?) I know in the USA many "HDTV" antennas don't receive VHF signals.

For a random address north of toronto, i get this report on tvfool
tvfool: maple,

which shows most in the direction of the CN tower(i think) but a few off in other directions.

It also shows several channels in the real 2-13 range which is vhf, which is sometimes harder to receive depending on your antenna.

It looks like you have a clearstream 2antenna , but i dont see great specs on what frequencies it receives and how well(other than a generic uhf+vhf).
posted by TheAdamist at 11:36 AM on August 9, 2017 [1 favorite]

The proof of the pudding is in the watching, but I think that the mounting next to wall will have little or no effect. I'd be less sure if you told me the was significant amount of metal, or other conductor in the wall.

Fifty years ago we had a TV antenna in our attic which picked up signals from NYC 40 miles away.
posted by SemiSalt at 12:54 PM on August 9, 2017 [1 favorite]

Thanks TheAdamist!
Yeah I'm good with the direction I'm pointing and where all the channels are broadcasting from. I'm getting all the ones I expect to; there are a few Buffalo ones that are spotty.
I guess my question was more if the placement of the antenna under the roof and against a wall is affecting reception, vs. above the roof with nothing behind it. Everything I've read only mentions the direction it's pointing.
On preview: SemiSalt, no metal or conductor that I know of.

And yes it's a Clearstream 2v antenna, sorry forgot to include that.
posted by chococat at 12:59 PM on August 9, 2017

The antenna has a 70 degree pattern, so the building wall behind it shouldn't affect the reception at all.
posted by vansly at 1:09 PM on August 9, 2017 [1 favorite]

It could cause a multipath issue that nulls certain frequencies, but you'd see either a much lower than expected signal strength relative to other starting at similar distances/broadcast power or a high signal strength with marginal signal quality.

Mounting that low definitely affects the signal strength enough that very distant stations may be unwatchable due to obstructions in the fresnel zones when they would be viewable were the antenna mounted well above the roofline. You're literally receiving less of the signal than you otherwise would. (Think of a partially shaded light bulb)
posted by wierdo at 1:44 PM on August 9, 2017 [1 favorite]

I have that exact antenna on a roof in DC. We're so close to everything we have a lot of multipath interference. As a result, siting and aiming the antenna was tedious. We have one broadcast tower we can see from every back window in the house (straight north); the other DC-specific local broadcast towers are on "Broadcast Hill," separated from the first one by almost exactly 90 degrees (more or less straight west). There's a single spot on the roof where we can get clear sightlines to the west, but it turned out to be impractical to mount the antenna there. When I found a spot I could actually mount the antenna, where I could get reasonable enough reception from the west, then I had to tweak it a lot to get the one tower to the north into one of the secondary lobes so that channel also comes in.

That antenna is good for VHF-HI (channels 7-13) and not great for VHF-LO (2-6). It is thus unlikely to pick up CJOH or CIII, whatever those are. You are unlikely to pick up anything broadcast on the opposite side of the house from the CN tower at all, but that doesn't look like much in the TVFool chart.

What I'd try before moving it to the roof is: (1) aim it to the southwest (away from the CN tower) at just such an angle it will pick up the channels being broadcast from SW and WSW, while still picking up the ones broadcast from the CN tower. That may or may not work. (2) remove the back grid and mount just the ring portion, and then try (1) again that way. The back grid serves no receiving function; it just acts as a shield preventing multipath interference. You may be able to receive channels bouncing off your house if you remove it, and then aim the antenna a full 90° west of the CN Tower.
posted by fedward at 2:26 PM on August 9, 2017 [1 favorite]

Yeah, there seems to be a sweet spot just west of the CN Tower, but only a very few degrees. If I go too much, it gets worse. This is the sightline to the Tower; the antenna is about 3' higher than this so it's slightly blocked by the big tree.
Just messed around a bit more, holding the thing in the air above the roofline while I texted my wife over and over to do a channel scan. Didn't seem any better, maybe one channel but hard to tell because the weather seems to be changing now. I eventually gave up and will try removing the back grid tomorrow.
On the bright side, the neighbours must be enjoying the performance. I've climbed headfirst out the 3rd floor window onto the 2nd floor roof about 30 times now; it's not pretty, especially when I climb back in with my ass and legs flailing out the window...
posted by chococat at 3:43 PM on August 9, 2017

Oh, that tree will cause serious signal attenuation. You may want the 4V instead of the 2V, just to punch through the tree a little better.
posted by fedward at 4:08 PM on August 9, 2017

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