OTA: The Big Trees Factor

21085 Views 55 Replies 20 Participants Last post by stampeder, May 23, 2011

stampeder

Discussion Starter · Jun 25, 2005 (Edited)

tigerbangs said:
Stampeder: get that 4228 and the 1111 up on the roof and quit your stalling!

Oh the irony! Here I am cheering on OTA converts, yet I can't enjoy it myself the way I'd like to! I am chomping at the bit to get those up and running but actually I've now done 2 test placements on the roof and the results were really awful due to the tall trees. I can't seem to find a sweet spot anywhere in the yard after dragging around my CM4228 on its mast, with my LG tuner with a 13" TV in tow. Also 4DTV_HD offered to come by with his spectrum analyzer to see if we can find one but I doubt that we would so I don't want to waste his time. I had to put my ugly little satellite dishes up on a 10' pole in my vegetable garden just to see the BEV sats.

My only choices are

1) put up a 60' tower
2) chainsaw massacre (illegal - the trees are protected, and we love them too)
3) move
4) climb that big tall fir tree and put all the gear up there (not!)

We'll see, but I tell ya its frustating, like having a Jacuzzi with no water connection.

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byebye_cable

· #41 · Aug 23, 2010

jgconnor said:
My Buffalo antenna (70 feet away from the Toronto one) points at a hole in a large maple tree in my neighbour's yard.

Did you make that hole?

There is an antenna tilt thread but it don't really get that specific about the line of tree's senario.

This website page I noted seems pretty specific though - point your UHF antenna at the visible horizon. In my case this would be the tops of the trees some 50 yards away.

http://www.hdtvprimer.com/ANTENNAS/siting.html

Still curious what the resident experts have to say about this.

jgconnor

· #42 · Aug 23, 2010

byebye_cable said:
Did you make that hole?

No, it I had, it would be much larger!

byebye_cable said:
point your UHF antenna at the visible horizon. In my case this would be the tops of the trees some 50 yards away.

I assume that there is a point at which this doesn't make a difference.

Do you have any other possible sites for your antenna?

As I mentioned, moving one of my antennas away from my tall trees made a big difference. This antenna is also not as high as my Buffalo antenna, but it works ok.

byebye_cable

· #43 · Aug 23, 2010

jgconnor said:
Do you have any other possible sites for your antenna?

No, this line of tree's runs alongside a park & is about 100 meters long before the first break. I'm pointing right at them, close to 90 degrees & there is NO way around (or over) from my house.

I'm slitting hairs I guess because I rarely have a problem. Just a perfectionist when it comes to antenna stuff...kinda like it

jgconnor

· #44 · Aug 23, 2010

byebye_cable said:
I'm slitting hairs I guess because I rarely have a problem. Just a perfectionist when it comes to antenna stuff...kinda like it

I hear you. I spent a lot of time experimenting and I'm pretty happy with the results (I cancelled cable, what's the down side?) but every now and then there are evenings when I lose some of my strongest channels.
Weather? Transmitter problems? Solar flares? Aliens? Who knows?

Even channels with 80% strength and 100% quality can fail for me sometimes.
Just the way it goes.

Satellite and cable aren't 100% reliable either.

byebye_cable

· #45 · Aug 25, 2010

hoopitup2000 said:
With all those trees you are a prime candidate for multipath. I have numerous oak and maple trees at close range with extreme levels of mutipath. I tried the 4228 and it performed miserably, even with plenty of signal strength. I then tried the 91-XG and now reception is excellent. I see no difference in reception regardless of whether or not the trees have leaves on them.

Did you point your 91-XG at the trees - or at the treetops (visible horizon)?

GeorgeMx

· #46 · Aug 26, 2010

Multipath Source Document?

I have not seen references to trees causing multipath problems with ATSC before reading some of the posts in this thread. Does anyone have a link or reference document that reports on trees causing multipath problems with ATSC transmission? Everything I have seen before relates to trees causing simple attenuation in the UHF frequencies.

byebye_cable

· #47 · Aug 27, 2010

http://www.hdtvprimer.com/ANTENNAS/glossaryG.html#multipath

It's when the wind blows that this becomes a bigger problem.

GeorgeMx

· #48 · Aug 31, 2010

byebye_cable said:
http://www.hdtvprimer.com/ANTENNAS/glossaryG.html#multipath

It's when the wind blows that this becomes a bigger problem.

I checked the reference which says "Short delay multi-path - This is always caused by something directly in front of the antenna. One common cause is a tree in front of the antenna. There will be chaotically overlapped signals behind a tree."

The tree is not causing multipath rather it is "something" (an obstruction) sitting in front of the antenna blocking the direct path from the transmitter. The main signal from the transmitter is attenuated making it difficult for the ATSC receiver to achieve a lock on the digital stream. When the wind blows and the folliage moves, the signal attenuation caused by the tree(s) will vary and may drop the signal level below the threshold for reliable lock causing data errors that result in picture and sound problems.

If an obstruction causes enough signal loss then the only signals the antenna captures will be from multiple indirect paths (multipath) that the equalizer in the ATSC receiver may not be able to resolve into a coherent stream. The tree is just an obstruction and does not create multipath itself.

I live in a poor geographic location for TV reception with plenty of folliage between the antenna (CM4221 in attic) and both CN Tower and Buffalo transmitters. I use a very high gain (22 dB) preamp and get the CN Tower stations and the main US network stations. NBC is not reliable particularly during the summer months but the rest are pretty good. In my experience, the high gain preamp makes all the difference when dealing with the trees.

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nitrof

· #49 · Nov 5, 2010

trees are loosing their leafs. Is it a possible explanation for increasing signal?

nitrof

· #50 · Nov 10, 2010

Trees loosing their leaves

Look at this link: Waves propagation

Trees and UHF
If a tree loses its leaves in the fall, reception behind it will improve dramatically. Many people get a TV for Christmas, and erect an antenna for it in January, and then wonder why it quit working in May. It’s the trees.

Aflipz

· #51 · Nov 30, 2010

According to the radio engineers I work with, it's a MYTH that leaves affect signal. They too believed that to be true for many years but it just isn't the case.

In fact, air temperature has a lot more to do with it; the colder the better.

ProjectSHO89

· #52 · Dec 1, 2010

Those radio engineers are obviously not working with 8VSB signals in the UHF band...

johnnysmoke

· #53 · Dec 2, 2010

I find I lose signals during the colder winter months. esp the weak signals in high UHF like Global. Warm weather with leaves on trees, and I receive a better signal.

stampeder

Discussion Starter · #54 · Dec 2, 2010

Regarding the effect of leafy tree groves or forests on TV reception, this is a well known attenuation and/or multipath phenomena that particularly affects the UHF band. The effect on VHF-LO is basically nil, while FM Radio and VHF-HI seems to do okay through leafy areas.

Rain, mist, fog, low cloud, sleet, and heavy snowfall are other environmental TV signal attenuators. If you have a leafy area between your antenna and a fringe to deepest fringe station you have a double whammy if the weather gets really wet. Here on Canada's "Wet Coast" it is readily seen as such weather patterns change. Quebec's Eastern Townships see quite a change when the trees lose their leaves for the winter.

ScaryBob

· #55 · Dec 2, 2010

Wet weather, in general, tends to make reception worse. That is especially noticeable in Summer because it kills tropo. OTOH, tropo can cause interference so reception may be better in wet weather if a decent LOS signal can be obtained. Can trees affect reception? Definitely, but I think some people in this thread are overstating the effect. Either way, it's easier to overcome signal attenuation from trees than from large hills or buildings with lots of steel.

stampeder

Discussion Starter · #56 · May 23, 2011

Late Spring in most of Canada this year

It has been a relatively late spring here on BC's south coast and much of Canada has had a soggy, gray spring so far, but now that the weather is getting warmer and the skies brighter the deciduous trees (maple, ash, beech, poplar, oak, elm, birch, etc.) are starting to really fill out, some blossoming.

As noted earlier in this thread UHF antennas are highly affected by trees, while VHF-LO are not, and VHF-HI usually are not.

Here on the West Coast the giant cedars and firs are in a growth phase too. My UHF 4-Bay bowtie reflector pointed at Mount Seymour is being touched by cedar boughs that were about a meter away last year! I have to get up there with my loppers today and cut them away again.

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