AVS Forum banner

Status
Not open for further replies.
1 - 20 of 29 Posts

·
Registered
Joined
·
304 Posts
Discussion Starter #1
I am having trouble with my UHF channels when it is windy. My one VHF channel seems fine. I have a yagi which is about 6 feet long, including the UHF component. I think this must be a dynamic multipath problem.


I think that directional antennas help with multipath problems. I tried an omni-directional first, and have much better results with this medium yagi. All 4 of my stations are 6-8 miles away in almost (but not exactly) the same direction. It is heavily wooded here in Atlanta. When it gets windy, the trees sway and my reception gets very flaky and I hate that.


So my question is: How directional are yagi antennas?


How many degrees apart can stations be to suggest rotation is needed?


Would a larger (UHF) antenna, more directional, help with my dynamic multipath problem, and would they require rotational adjustment (i.e. how directional are yagi antennas)?


Please reply in degrees, not radians.
 

·
Registered
Joined
·
24 Posts
example of a yagi antenna by Lindsay:


ch: 2 to 6 = 60deg beamwidth

7 to 13 = 36 " "

14 to 69 = 34 " "


As far as loosing the picture when windy; something is wrong with either

the tower,mast,& or guying of the mount system.


Check all electrical connection that could be loose.
 

·
Registered
Joined
·
1,525 Posts
cbgenrich,


I have a 4248, some weak channels are +/-3 deg, strong channels can be +/-20 deg. Are you using a rotator? They are a must.


Glenn
 

·
Registered
Joined
·
304 Posts
Discussion Starter #4
I'm not using a rotor, nor do I want to start. I'm not that far from the transmitters, and they are pretty well clustered together (about 30 degrees total spread). On the following map, I live at the "Tucker" label northeast of the transmitters.

http://groups.yahoo.com/group/ahdtv/...Atlanta-DT.gif


I'm starting to get answers; if they are 30 degrees apart, then I shouldn't get a longer antenna unless I want to get a roter, which I don't.


I'll check the stability of my antenna next time it's windy. I just figured it was the trees. There is a giant transmitter tower pretty much directly between me and the DTV transmitters, but other than that no obvious source of multipath distortion, especially wind sensitive sources. My current setup works very well when it isn't windy, so I think I am close to having done all I can.

 

·
Registered
Joined
·
1,084 Posts
Quote:
Originally posted by cbgenrich:
I'll check the stability of my antenna next time it's windy.
Don't underestimate the role a poor cable connection might play in your troubles with wind. Before I went digital, I had a severe wind related problem with the analog signals whenever we had one of our periodic "Santa Ana" winds where I live. I tried everything to lock a better, more consistent signal by checking the aim, guying, etc. Everything except the coax, that is. It turned out I had simple loose connections at two places in the line. Once secured, the reception never wavered thereafter regardless of the severity of the wind (sometimes over 60 mph). The poor connections weren't the result of the unions completely separating, but apparently the grounding (threaded connections) were whipped in the gusts just enough that it broke signal continuity frequently and randomly.

 

·
Registered
Joined
·
1,525 Posts
Quote:
Originally posted by cbgenrich:
I'm not using a rotor, nor do I want to start. I'm not that far from the transmitters, and they are pretty well clustered together (about 30 degrees total spread). On the following map, I live at the "Tucker" label northeast of the transmitters.
I can pick up 2 San Diego channels 113 miles away, transmitted from the same location. Channel 25 comes in best at 142 deg, ch. 55 comes in best at 147 deg. Once you try a rotator, you will realize its importance in locking in the signal.


Glenn

 

·
Registered
Joined
·
18 Posts
I am also having problems with my Fox station (ch 31) breaking up when it is windy out. My 2 VHF and other UHF stations (ch 15) are fine. I know it's not a loose connection since my RS yagi antenna is in the attic (only choice right now). I get strong signals now in the 70-90 range but ch 31 bounces from 0-70 whenever it gets windy. I was going to add a preamp but I believe it will not reduce multipath interference. Would a dedicated UHF antenna help reduce multipath? Will a good preamp help any?


[This message has been edited by Scott Moore (edited 04-20-2001).]
 

·
Registered
Joined
·
18 Posts
I am also having problems with my Fox station (ch 31) breaking up when it is windy out. My 2 VHF and other UHF station (ch 15) are fine. I know it's not a loose connection since my RS yagi antenna is in the attic (only choice right now). I get strong signals now in the 70-90 range but ch 31 bounce from 0-70-30-70 whenever it gets windy. I was going to add a preamp but I believe it will not reduce multipath interference. Would a dedicated UHF antenna help reduce multipath?
 

·
Registered
Joined
·
516 Posts
Scott,


Maybe you have some tree blowing around which, due to localized topography/geometry with Fox's tower, causes dynamic multipath (possibly frequency dependent). Perhaps it could be minimized by repointing or changing to a different antenna with narrower beamwidth or higher front-to-back ratio in case the reflections are coming from the side or rear. Or how about adding a Blonder-Tongue model BTY-10-U/C (ch. 31) yagi using a Channel Master model 0585-2 separator/joiner?

http://www.blondertongue.com/WebPage...ingleCh_01.pdf

http://www.channelmaster.com/pages/cjs1.htm


------------------

George at WNDU
 

·
Registered
Joined
·
1,267 Posts
Hate to say this but most people resisting rotors really need them. The beam width is not the only consideration to tell if you need one, if you are in a bad multipath area.


Most people have excess signal strength, and can afford to be off from the main beam anyway. What is critical is where the multipath is located, and where the side and rear lobe nulls are. These can be very sharp (compared

to the front beam width)!


As others have mentioned, you can have several stations at the same location, and still have to aim the antenna differently (due to the effect of channel frequency on the multipath), if you want good reception without dropouts.


So if you can get good reception without a rotor, great, you are very lucky.
 

·
Registered
Joined
·
1,084 Posts
Quote:
Originally posted by Engine-Ear:
Getting 30 or 40 million people to "be proficient" ... seems like an unlikely approach to making HDTV work.
HDTV works just fine if it arrives by cable or DBS. What I believe you really meant is "digital OTA" (which would include HD OTA). On that score, sadly, you hit the nail on the head, and the more I read, the more I've come to suspect that the modulation method (the FCC's and the NAB's favorite vs. Sinclair's favorite) is largely irrelevant in this issue. There are soothing promises of better days to come with further development, but the breakthrough was supposedly to arrive with 2nd generation STBs. Time'll tell if the 3rd generation boxes will deliver when they eventually arrive...

 

·
Registered
Joined
·
5,200 Posts
Quote:
Originally posted by Engine-Ear:
Getting 30 or 40 million people to "be proficient" in all of that (And to move their antenna a few degrees towards the south) seems like an unlikely approach to making HDTV work.
IMHO, The introduction of H/DTV OTA had two grave errors in the way it was introduced. 1- Complete lack of training for everyone involved and 2- The feedback a H/DTV set and/or STB gives to the user trying to set-up the system. A quasi signal meter just does not cut-it.


Proof: DirecTV and Dish users has to have the antenna precisely aimed and can-not have obstacles in the path. To date, they have about 15,000,000 users, so the rigid antenna (dish) requirements does not seem to be a deterrent.


I have stated here many times, no RF, no Reception. On the flip side, look at the number of people here that get H/DTV stations 40, 50, even 60 miles away. In most cases, NTSC (UHF) at these distances will be snowy.


------------------

Wendell

Technical Services Supervisor

MAETV
 

·
Registered
Joined
·
5,200 Posts
Quote:
Originally posted by Engine-Ear:
Using a rotor to reduce multipath or maximize the signal(Tune the station) can be a very frequent requirement. And there really isn't any good way to know if you will be successful when you install an antenna initially. But I do believe that additional power can reduce much of this complexity.
EE, all your points are well taken, but I think if the prospective buyer/user is properly informed, then there will be far fewer complaints about H/DTV reception. It is a complex process and needs to be properly presented and explained to the buyer. Many of us have said from day one that the H/DTV receiving device needs to provide much more feedback than all models presently do [and its imperative to be on the local cable system]. To connect a H/DTV STB/receiver up, tune to your known channel, then have the device sit there and display Weak Signal, No Signal, etc. will not win it many friends (it took me awhile to figure out you had to do a scan before it would work).


More power could help in many (most?) situations, could be a hindrance in others!


P.S. I wish that I had a quarter for every time I pointed someone to Rich Peterson's DVB FAQ, or Jim Talyor's DVD FAQ, or ... AFAIK, there is no FAQ for H/DTV


------------------

Wendell

Technical Services Supervisor

MAETV


[This message has been edited by Wendell R. Breland (edited 04-22-2001).]
 

·
Registered
Joined
·
304 Posts
Discussion Starter #15
I have spent dozens of hours, perhaps many dozens, getting satisfactory antenna performance. It was easy to get reception, very difficult to get highly reliable service without futzing with the antenna every time I changed channels. The expense (not including the STB) has not been great, but the effort has. It is difficult to imagine most going through this. In the end, I get great PQ almost all of the time for free, and that's nice.


It was windy Sunday afternoon and I had some time to try some things. The only time I can even try to improve my reception is when it is windy, since the reception on all 4 available channels is flawless the rest of the time (without a rotor).


I realized that a tree branch or two was just barely able to touch the antenna. Perhaps wind caused an intermittent phenomena with respect to that, so I risked life and limb and eliminated that possibility. This had no effect http://www.avsforum.com/ubb/frown.gif


I watched the antenna sway in the wind to see if I might need guy wires. I could see it move, but not much. The long wings moved some, which guy wires wouldn't help. The whole antenna moved as well, but not much. Maybe an inch of sway, irregularly. http://www.avsforum.com/ubb/rolleyes.gif


I marked the original rotation of the pole which represents the angle which has worked well for me for several weeks. After observing occasional dropouts for some time I tried rotating the antenna in roughly 6 degree increments. This just made matters worse and it didn't take that long to figure out that I already had it pointing in a very nearly ideal direction. In the end I left it about 3 degrees off the original. http://www.avsforum.com/ubb/smile.gif


Conclusion:


I'm about out of ideas on how to improve things. It is extremely difficult to diagnose, because I can only work on it when it is windy (and I'm available and it's not dark or rainy).


The only clear option may be to get a more directional antenna and a rotor. I really would hate to do that unless I could be very very certain that it would solve the problem.

http://www.avsforum.com/ubb/confused.gif
 

·
Registered
Joined
·
304 Posts
Discussion Starter #16
I have one of those preamps installed. It is a Radio Shack unit, and it does provide more signal strength as observed on the STB tuner display. I also have a medium sized yagi and only live 6-8 miles from the transmitters, and used RG-6 cable, and installed outdoors, and everything else I could think of to ensure I don't have a signal strength problem. I don't think I do, because I either get a solid indication from the signal meter (and a picture) or no signal on the meter (and no picture). That, and the fact that the omni-directional didn't work well has convinced me that I have multipath problems. When the wind blows, it gets to be too much for the system.


I am sure that I have tight connections because I put it up myself and I built it on the ground and even put electrical tape at the connections. I couldn't use the rubber boots because they didn't want to fit over the molded connectors that came with my cables. I prefer to let the machines put the connectors on.


I do about 65 feet of cable, and there is a grounding block 15 feet down from the top which is rather like a barrel. I don't see how these could be problems, or eliminated.


After the indoor unit of the amp. I split the signal once to the STB and the other side is distributed to the rest of the house for analog purposes, being split a number of times and some of those possibly unterminated. It is my understanding that the 1 to 2 split before the STB cuts the signal in half, but that whatever happens on the other side of that split is largely irrelevant. I've been known to eliminate all the splitters to try to get the STB to work more reliably, but there's no silver bullet there. I'm interested in thoughts on the effects of splitters and unterminated ends anyways.


Now I'm thinking that a rotor may not be such a bad idea. It's really not tollerable to keep changing the rotation with every channel change. But now that I think about it, I only have to do that when it's windy. And the ability to use it for diagnostic purposes alone may be worth the cost and trouble of installing it. http://www.avsforum.com/ubb/wink.gif Could also help with the occasional need to watch something analog. I'm thinking: Why not install a rotor?


However, a more directional, higher gain antenna is probably not a good idea, because it would make the normal non-windy reception more likely to require rotation. http://www.avsforum.com/ubb/frown.gif


Still, I don't understand the source of my multi-path problem, especially the wind related multi-path. I've polled others in the Atlanta area as to their wind related difficulties, and my problem is clearly worse than most. Possibilities include:


o Large (unrelated) transmitter tower almost directly in my path.

o Huge (600 ft high) granite outcropping 90 deg off axis with an extra 8 miles of path.

o Generally forested landscape in the Atlanta area (would affect most others in the area but does not appear to).

o My antenna moves in the wind (not much by my observation, but not guyed).

o Atmospheric phenomena such as skip.

o My STB doesn't deal with multipath well (it is the recently developed Samsung SIR-T150, one of the 2nd generation units I should think).
 

·
Registered
Joined
·
1,084 Posts
Forgive me, cbgenrich, for what may seem like needlessly flogging a dead horse, but it might be illuminating to get up on the roof on a calm day and lightly whip the lead-in while someone in the house watches the TV. If this maneuever results in the same signal loss you experience in windy conditions, it's almost certainly a connection/cable indictment. Even factory-made cabling can be defective or develop defects. (That's why I roll my own... http://www.avsforum.com/ubb/biggrin.gif ) Also check the active elements on the antenna - those mounted with plastic insulators to the boom and tied electrically to the "multiple drive system" of alternately crossed-over bare wires that eventually lead to where the lead-in connects. If your antenna has a two-piece boom, verify that both bare wires are properly attached to their respective connecting studs with wingnuts on the insulator closest to where the two boom segments join. Especially look for the possibility of intermittant "shorts" to each other or to the boom at the cross-over points because of insufficient spacing. If you suspect any particular areas, don't hesitate to bend the wires a bit further apart. The wires should be separated by at least 1/2". Check the insulators that individual active elements aren't shorting against something because of a crack or break.


[This message has been edited by Ray H (edited 04-23-2001).]
 

·
Registered
Joined
·
5 Posts
Put this in the for what it is worth category. Since you are so close to the transmitters, I wonder if a 6' yagi is really necessary. Generally speaking, antennas of that type are designed for longer distances of 50 to 60 miles.
 

·
Registered
Joined
·
1,525 Posts
Quote:
Originally posted by cbgenrich:


If I take the indoor portion of the amp out of the signal path, would the outdoor portion become largely irrelevant? Or would it damage the signal if it didn't get it's DC power? I'm thinking of trying the system for a while without it on the basis that I should get enough signal from an outdoor yagi of this size. I may have installed it before I got the direction figured out as well as I have it now.


[/b]


When I bypass the amp, I install a barrel connector in place of the amp and unplug the power supply. The signal goes through the power supply with no problem.


Glenn
 

·
Registered
Joined
·
304 Posts
Discussion Starter #20
Quote:
When I bypass the amp, I install a barrel connector in place of the amp and unplug the power supply. The signal goes through the power supply with no problem.


Glenn
My "amp" is connected directly to the antenna. I'd have to replace it with a 300/75 adapter, after taking the whole thing down from the roof.


I was thinking of leaving the amp in place and simply skipping the power supply indoor unit.
 
1 - 20 of 29 Posts
Status
Not open for further replies.
Top