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Dumb question about antenna pointing.
I've been having fits with my OTA channels.
Long story short, one channel and it's sub is VHF, all the others are UHF.
So I have a separate VHF and a separate UHF antenna with a signal combiner and a preamp about 20 feet up on a pole next to my house. I had to put the antennas outside because of I have a steel roof so inside the attic was totally impossible.
I can't get the antennas any higher because it would take a cherry picker to get up any higher. As it is now I have to stand on the peak of the roof to adjust it and that's scary enough.
The other problem is that the transmitter antennas for the local stations are scattered all over the place.
Most antennas are generally north of my house but two of them are to the west.
On of those two is RTV and I'm not really too worried about it. The other one is MeTV and I am getting it now but it's weak and drops out a lot because my antenna is pointed more or less to the north.
I have a 10' C-band that I pick up MeTV and RTV on but I also like having it on OTA because my Dish tuner can receive OTA and it's nice to have everything in one tuner.
So I went to Wikipedia and looked up all my local broadcasters. I followed the links to the FCC site where I downloaded Google Earth KML files for the location of each antenna of all the local stations I can receive.
I loaded them all into Google Earth at once and I can see where all the antennas are and it also shows a circle where I suppose if you're in the circle you should get the signal. I do get all the channels, that's not the problem, it's signal strength and aiming that is.
So with each antenna pinpointed, I used the drawing tool in G.E. to draw a straight line directly from my TV antenna to each TV antenna tower. I made them each in a different color.
One of the lines points to the one antenna that is transmitting the VHF signal, for that one, I have an antenna I can aim at it.
As to the other UHF towers, they are pretty much all to the north and I'm thinking that if I just ~average~ them then aim towards the average center of them, that should be good enough. Right?
But, what to do about the ones to the west? That's a full 45 degrees off from where I need to aim for the others. I've been thinking I need to add another UHF antenna, aim it to the west and use a special signal combiner that is designed just for this sort of situation.
But the aiming thing that's messing with my mind is, aren't you supposed to point the antenna in a perfectly straight line towards the transmitter? If say the transmitter tower is at 270 degrees, wouldn't I aim my antenna straight at 270 degrees? I ask this because even though ~ I KNOW ~ where the towers are and in theory pointing at them should get me the best signal, I've found that I actually have to aim a fair bit off from where they are to get the strongest signal. That doesn't make any sense to me.
Is there some secret to aiming OTA antennas? I've looked into buying a meter similar to the ones I have for FTA and DBS but those are really way too expensive for me.
I have a little 7" TV but I can't use it up there because of the preamp. I can put the video from my Dish tuner into a capture card on my PC and use WIFI to view the video on my iPhone up on the roof but when I put the tuner into a mode to display the signal strength bars, by the time I climb the ladder and get to the antenna, the tuner times out and returns to normal viewing sans the signal strength meter..
So really the only way for me to do this I suppose is use the google earth stuff I did to help me aim the antennas. Is my picking the average direction the right way to go about this?
I'm not including the antennas to the west in this because if I do it causes the others to take a hit in signal strength for the ones to the north.
Here's a screen shot of the lines from each transmitter tower to MY antenna.
The green line is to the one and only VHF signal. There are two channels on it, a main and a sub channel. For that I have a separate VHF antenna I can aim that way.
The amber, cyan and red lines are three UHF signals, each of which has a main channel and a sub channel. For this I have a separate UHF antenna I can aim down the middle of these.
In reality, if you follow them out to the towers, the tower are many miles apart, two of them are less than 15 miles and close to each other (amber/cyan), the red one is like 40 miles to the north and probably 10 miles east of the other two. But the lines all are in the same general direction from me.
The black line is the UHF for RTV, it's very low power and weak. I really don't care if I can pick it up or not but it would be a bonus if I could. Currently it comes in but it's horrible. It's unwatchable so I don't bother.
Besides, RTV ain't what it used to be and I don't really worry myself over it anymore. And then of course there's the fact that I have a gaggle of ku dishes and several large C-band dishes I can get it on anyway.. So, meh....
The blue line though, to the west, has the local Me-TV. It carries two sub channels for the same broadcaster that is transmitting the green VHF line above. They bought up a bunch of small local independent channels and changed the content. One of them was an Azteca channel which they just converted to MeTV. I don't know why they own four different channels but broadcast from two different towers that are spread so far apart.
I see no other way to pick up the two channels on the blue line without adding another UHF antenna and combiner. I would aim the second UHF antenna dead on the blue line and not worry about RTV on the black line. RTV is in that general direction so if it happens to come in then fine. If not, boo hoo.. All I want is the strongest signal on the blue line. Besides, I get MeTV on C-band but when I can get it OTA I can also watch it on my Dish Network tuner via it's built-in ATSC tuner so that's handy, switching back and forth between tuners is a bit of an annoyance, the home theater PC blows up when the display is switched off of it to something else and I end up having to crash it to recover the video. Stupid windows!
As it is now, my antennas are not pointed at the towers because doing so causes problems with other signals. But then again, I had never sat down and plotted out where the towers really are as I have this time, I had just blindly aimed the antennas in the general direction I ~thought~ the towers to be. So before it was all just hit and miss, trial and error. But now I want to be scientific about it and do it right.
Is there ever any situation where you would not aim the antenna directly at the broadcast tower? If a tower is at 20 degrees from me, wouldn't I aim the antenna at 20 degrees north? Wouldn't I follow the lines I plotted on google earth from their towers to my antenna? There would never be a case where I would instead aim my antenna at say, 45 degrees when the tower is at 20 degrees, no? Like bouncing the signal off stuff?
The land here is __F__L__A__T__. No hills, no obstructions other than the curve of the earth and from what I can tell, my antenna is plenty high enough to compensate for that. TV signals travel a straight line like lasers, right?
There is a full oak tree in the way of all of the signals to the north of me and there's little I can do about it. I can't move the antenna to anywhere else, it has to stay where it is. I can't afford to have the tree cut down though I wish I could. As it is, the tree doesn't seem to impede the signals too much, the signals to the north come in fairly strong.
My sense of direction is not good so when I get up on the roof and look at things I sort of have trouble envisioning where things are. Thank goodness for GPS!! And believe it or not, I even get lost with a GPS. Often... So that's why I had to resort to google earth to try and figure this mess out.
I could use some advice, I think I'm trying to over-think this thing and it's making me crazy.
Last edited by Dee_Ann; 03-27-2012 at 09:49 AM.
03-27-2012 09:44 AM
You are working too hard. You can get all this information, plus signal strength and necessary antenna height from TVFOOL.COM. Just type in your address and it will provide a map and list of everything you can receive.
The oak tree is a problem, and is providing some major attenuation. It would be best to move the antenna to where it would clear the tree on line of sight to the towers. However, if you are getting the signals from there, don't worry about it. Is the tree currently in leaves? If it is still winter bare, you may have problems as it leafs out.
With that much difference in direction, you really only have a few choices. Either go omnidirectional if the signals are strong enough, put up a second UHF antenna and use a combiner, or install a rotor.
Yes, ideally, you would point your receiving antenna directly towards the transmitting antenna for highest signal strength. However, adding into the mix such things as your angled, metal roof acting as a partial ground plane (and other buildings, trees, etc. reflecting and antennuating the signal) and things get a little more complicated. These things could be modeled to provide a better approximation of where to aim your antenna, but it's much easier to simply rotate the antenna until you get the highest signal.
Also, directional antennas can receive (and transmit) effectively in directions other than their "front." Google "antenna lobes" images and you'll find antenna radiation patterns with smaller side radiation lobes (and some with rear lobes that are nearly as large as the front lobe). The radiation pattern shows how effective an antenna transmits to (or receives from) different directions. (Hopefully), I've attached an image that shows how the height of an antenna (a dipole is modeled in the image) can also change its radiation pattern. This also may help explain why you have to turn your antenna slightly away from the transmitter.
Your antenna options were summed up nicely by jayn_j, and I second the suggestion for using TVFOOL. I considered multiple antennas at my location, but I ultimately installed a rotor, and haven't had any reqrets with that decision.
I went to TV Fool and their data is out of date. Many sub channels are not listed, this is a problem because some sub channels may come from the same parent channel but are transmitted from different physical locations.
Their google earth KMZ files won't download, they offer them only via bit torrent and the torrents are dead. No seeds, no peers, no download..
I can't find much there of any use to me.
Oh, and their little pie graph thing, it's so cluttered with cr*p channels that are dead anyway that you can't read it. And you can't filter out the dead garbage channels.
The concept is awesome but they've left it to go to rust and it is in bad need of updates and ways to filter out junk you aren't interested in.
Oh well. It looks like I didn't waste my time doing it myself..
Sorry that didn't work out for you. There is an alternative site at
AntennaWeb - Home
that might have better data in your case, but both receive their raw data from the FCC database, so it wouldn't help the subchannel issue.
The metal roof will definitely affect reflection patterns. The tower will help, but you are going to need to sink a significant part of one section into the earth to get something stable. Figure on no more than 35 ft of elevation from it, and more likely around 32'. I guess I would mount a rotor when the tower work is done and then you can adapt to changing conditions. Otherwise someone will need to be constantly climbing that tower.
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