Question: line of sight, except that it isn't?

Cyril279

DTVUSA Rookie
#1
Summary:
I have read over and over again about these UHV/VHF antennas needing line-of-sight, and that they simply won’t see through trees, or other homes, but my current setup seems to receive reliable signal through both. Why/how is this?

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=2c157b72c18402

Setup:
Antenna -> pre-amp ---50’--> power -> splitter ---15’--> Tuner1
…splitter ---30’--> Tuner2

Background:
I am an recent-cord-cutter, and therefore an antenna noob.
I am in a single story, stand-alone home with aluminum siding. I am surrounded by two-story stand-alone homes with aluminum siding, AND trees (both evergreen and deciduous). The aluminum siding is why I did not attempt an indoor antenna.

FEB 2014, I started with an attic installation of a RCA ANT751 +pre-amp (split to two tuners), since the antenna specs seemed to cover the range that I was looking for, aimed at magnetic 173*; but was having trouble getting reliable signal on a few channels (most notably PBS, CBS, FOX, & ION).

I migrated the attic installation to an outside eave-mast (already attached to the house from a previous direct-TV installation) and signal improved, but the trouble-stations were still unreliable, and very susceptible to weather changes (the antenna was again aimed at magnetic 173).

*I realized today, 2015/01/05, that this should have been TRUE 173 (Magnetic 184).

DEC 2014, My wife was tired of the spotty reception on the football channels. The better answer would likely have been to erect a taller mast, but considering that we seemed so-close, while using such an itty-bitty antenna, we went the easy-route, and simply bought a bigger one (Winegard HD7697P). We gained several channels, and the trouble-channels (so far) seem much more reliable. One stupidly windy day let us know that we still weren’t impervious to weather changes; we were able to watch the game, but it was annoying at times. The antenna definitely improved the reception, but I was a bit surprised that it seemed sensitive. <-- maybe I should stabilize the antenna-end somehow?

What seems to have had a notable effect:
- Relocating to the roof
- Grounding the splitter (to home AC system)
- Re-aiming the antenna (tvfool and antennaweb report true north, not magnetic north)
- Re-terminating a few crimped coax-connectors (someone else’s crimps from a prior installation)
- Reduced run-lengths

So now we’re looking better, but the angle correction has the antenna pointed directly at our neighbor’s second-story aluminum siding. After the reading that I’ve done thus far, I didn’t expect to receive any kind of useful signal with an antenna pointed at a tin box surrounded by trees. I don’t plan on rocking the boat, but I’m sure curious to know how it’s still afloat.

p.s. I have read that vertical vent tubes will likely NOT affect signal, but the roof flashing might? Does that mean that one of those spinny-turbines would affect the signal?

-Cyril
 

Cyril279

DTVUSA Rookie
#2
Steve, I don't trust "civilians" (no offense, Bryan) when they disagree with TVF on line-of-sight. Most people think they should literally be able to see the transmitter, or at least that it's straight across from the antenna.

Bryan, if you can imagine a line at a 20° upward angle from the top of your antenna, does that slam right into those trees or a building? From looking at the radar plots, 20° should be enough clearance. It's OK if it skims the treetops, you just don't want ALL the signal plowing through lots of leaves.

Rick
Ah, then "line of sight" is definitely different than what I was thinking.

View from my antenna:


That next roof-peak is around 6° degrees from where I'm standing, and above it is much-more like clear-sky.

The mis-aimed efforts (~162) all point into the trees, and could explain poor reception of some channels, especially during the summer months.

So in theory, the ant751 may have been suitable if correctly aimed...
 
#3
It sounds like you are just going through the normal learning process of establishing good OTA reception at your location. In a world of direct, reflected, diffracted, multi-path, and layered signals you learn to place and aim the antenna where it works best for your location. Which might not be where you or anyone else thinks it should work best. In the real world the cleanest signal is not always achieved by aiming exactly at the transmitter. If you have never looked at this page on antenna siting it is a good read.
http://www.hdtvprimer.com/ANTENNAS/siting.html
While it can't explain how to work around all of the variables that can be going on at a given location. It does give you some insight as to some of the effects environmental objects have on signals.
Steve
 

Cyril279

DTVUSA Rookie
#4
It sounds like you are just going through the normal learning process of establishing good OTA reception at your location.[...]
It seems that this learning process, according to how far you push it, could get time-consuming, expensive, and/or frustrating very quickly; while possibly yielding far less actual improvement than practical knowlege or assurance.

I appreciate the info link.

In your opinion, what is the likelihood of those aluminum attic-exhaust pieces having a negative affect on signal reception?

-Cyril
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#5
:welcome: Cyril

Free OTA reception is pretty straight forward as long as you believe in black magic and pixie dust. Yes, every metallic object (especially attic fixtures and metal roofs) 'might' totally wreck or contribute positively to your reception, so as Steve suggested, keep trying different antenna locations before you permanently mount it. Up/down/right/left/forward/backward and eventually, you will find a hot-spot for it. To establish new channels you have to tell your tuner to 'scan for new channels' every time you move your antenna, so it will be a lengthy process.

Regarding NON-line of sight reception, here is one way it works: picture yourself standing on the side of a road a quarter mile from the top of a hill at midnight. A car is climbing the opposite side of the hill has its headlights on. Before you have a direct view of the car, you see a glow like a sunrise or sunset. You cannot see the car nor the headlights but you know its there because there is refracted light. Not much light, but as in the case of OTA Digital reception, signal levels or strength barely matters: it only requires a clean data stream.

Solid reflections rarely happen but I have a personal example: there is a transmitter almost due east of me, shadowed by a tall hill. However, I have a straight 'shot' at the downtown skyscrapers and sure enough, I have a dependible reflection off of a building. My antenna must be at a specific height, not even 6" higher or lower and finding this reflection was a fluke and it works for me.

Jim
 
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