Utter (and long) confusion on OTA and Satellite coordinates

[Vicki]

Too much info just strains my brain... Following some very helpful links that elocs posted in the Help Desk forum, I found myself in a state of confusion. I'm trying to figure out exactly what my next installer will need to know and do to get it right the first time. Here's how I got confused...hope someone can straighten me out...

Most of the OTA stations I am interested in getting show a compass setting of 184.8 to 186.2. NBC at 185.1 is the channel I most want to insure good reception on, so if my antenna pointed pretty much at 185.5 (splitting the difference of the range of settings) would that work?

All the channels I want to receive are within about 45 miles according to both http://www.2150.com/broadcast/default.asp and http://www.antennaweb.com although the compass settings as well as mileage figures differ slightly between them, with antennaweb ranging from 184 to 185 on compass settings.

I found this link http://tiger.census.gov/cgi-bin/mapbrowse-tbl and used it to zero in on my city by zip code, then moved the marker to my exact location, to determine my exact latitude and longitude, rather than using the generic one for my city as well as to double check Magnetic Declination. (But unless you live in a pretty mountainous area, I doubt the exact latitude and longitude are really necessary.)

I came up with the same Magnetic Declination calculations on this link http://www.2150.com/broadcast/default.asp (using both exact and generic coordinates and putting in longitude as a negative number as instructed), leaving the Magnetic Declination space blank. It calculated a Magnetic Declination of 14.56 (no direction indicated and not negative). Using this site http://www.ngdc.noaa.gov/seg/geomag/jsp/struts/calcDeclination to calculate Declination, it shows 14.56 E (not negative either, but does include a direction).

Does that mean I subtract that number even though neither are shown as negative, since I am in the West? That's what I gathered the following link intends.

With my coordinates, this link for azimuth angles http://www.csgnetwork.com/antennasatelazposcalc.html calculated an azimuth angle of 110.0 and elevation of 14.7 for Rainbow1 at 61.5, or 118.3 azimuth and 22.5 elevation for AMC6 at 72 (if things go that way down the road).

So is the idea to deduct the elevation number from the azimuth number to get the exact angle for my location?

Is the number described as “elevation” the same thing as the number for “Magnetic Declination” above? The numbers are very close for Rainbow1 (but not for AMC6) from both calculator sites.

If they are not the same, do I deduct the Magnetic Declination from the azimuth after I deduct the elevation?

Is there a special tool for determining the final result for the azimuth angle, or is it just a matter of setting that number on a compass reading from magnetic north?

Can anyone help me get straightened out...or am I too far gone?? Vicki
P.S.: I could be worse, I guess...I haven't even started the cocktail hour yet!!

 

[TYORK]

WOW you have got me total confused to i can tell you that you are right on the antenna should be set at 185 now for the rest of your question i will have to study it a little more.

 

[greyghost]

Let me try to simplify this for you.
1. Azimuth and elevation are unrelated to each other. Azimuth is the direction (north, south, east, west) that you will be pointing the dish or antenna. Elevation is the angle that you will be tilting the dish toward the sky. You are never adding or subtracting one from the other- they are unrelated to each other.
2. Don't worry about "magnetic declination". This is a technical term refering to the difference between true north (the north pole) and magnetic north (the point toward which your compass will be pulled). It is of no use to you - just follow the azimuth given on antennaweb.org- it is the one thing on the site that is always accurate.
3. With a directional antenna, anything more than 15 or so miles away is in the same direction if the azimuth is within about 30 degrees. That is to say, something at 180 degrees is in the same direction as something at 150 degrees. Again, generally speaking. The antenna will still need to be tweaked in one direction or another to get optimum signal, but, all other things being equal, if you can get a station broadcasting from 180 degrees, you will be able to get a station broadcasting from 150 degrees with the same directional antenna. So... 184.8, 186.2, 185.1, 185.5, are all the same. Point the antenna as close as you can reckon with your compass and see what you've got- tweak from there (I'm assuming you don't have an off-air meter).
I hope this helps.

 

[Vicki]

WOW you have got me total confused to i can tell you that you are right on the antenna should be set at 185 now for the rest of your question i will have to study it a little more.

Thanks TYORK...I was afraid my muddled explanation would only serve to cause more confusion!! I've PM'd you a little more specific info on my exact location, hoping it may help clarify my muddled explanations...

Let me try to simplify this for you.
1. Azimuth and elevation are unrelated to each other. Azimuth is the direction (north, south, east, west) that you will be pointing the dish or antenna. Elevation is the angle that you will be tilting the dish toward the sky. You are never adding or subtracting one from the other- they are unrelated to each other. OK, that makes sense, but why does this site http://www.2150.com/broadcast/default.asp say: “ Enter the latitude and longitude of your location and press the button to see broadcast television stations within the given range of your location. Use the magnetic declination field to correct for compass headings.”? It appears as if the calculation automatically does this (when used as presented, a positive number) and brings the results more into agreement with the antennaweb compass settings, but I was thinking I still needed to make an adjustment. I admit I missed the note on atennaweb that said “Please note that "Compass Orientation" is referenced to magnetic North.”
2. Don't worry about "magnetic declination". Even for the satellite positioning?
This is a technical term refering to the difference between true north (the north pole) and magnetic north (the point toward which your compass will be pulled). It is of no use to you - just follow the azimuth given on antennaweb.org- it is the one thing on the site that is always accurate. Based on my response above, would you consider this new site to be more accurate than antennaweb? It certainly seems to give a lot more info about the stations.
3. With a directional antenna, anything more than 15 or so miles away is in the same direction if the azimuth is within about 30 degrees. That is to say, something at 180 degrees is in the same direction as something at 150 degrees. Again, generally speaking. The antenna will still need to be tweaked in one direction or another to get optimum signal, but, all other things being equal, if you can get a station broadcasting from 180 degrees, you will be able to get a station broadcasting from 150 degrees with the same directional antenna. So... 184.8, 186.2, 185.1, 185.5, are all the same. Point the antenna as close as you can reckon with your compass and see what you've got- tweak from there (I'm assuming you don't have an off-air meter). You’re 100% right about the off-air meter! I had one good installer during my sad odyssey last summer, and he was the only installer who had one. I gather they are expensive, so that won’t be on my shopping list! So, if my primary priority is NBC at 185.1, splitting the difference using the humble compass, will probably do the trick for OTA pretty well, right? But what about satellite positioning? Is a special tool required to get the right angle?
I hope this helps. I think it has, but your response to my responses may tell the tale for me! I just want to make sure that I don’t leave any stones unturned in this effort! Thanks for your helpl!

 

[greyghost]

Vicki, I tried the various sites you listed, and some that those sites listed and am now certain of what you need to do. Ignore all that crap. I feel like I just tried to take an advanced calculus exam that was all word problems written in hieroglyphics. You are right, it is very confusing and frustrating- the numbers don't quite work out- at least I couldn't get one site to agree with another regarding the direction of my stations. In any case, all you need for direction is antennaweb.org. Understand, this is not an exact science. If you were to draw a straight, visible line in the air from you to the transmission tower (let's say you are the cookie monster), your antenna may not even be pointing down that line. And that's for one tower. Now throw in multiple towers in multiple locations and there is no way to predict exactly where your antenna needs to point. In addition, if you use a directional antenna, especially a small one, you may need to move the antenna three feet back or two feet to the left- this has to do with wavelength. There are many variables. It is not an exact science. It really is trial and error. And a meter only makes the trial and error process quicker.
Now, a dish is different. If you have a line of sight to the satellite, then you can mount it anywhere that you have that line of sight. Point it as best you can in that direction. Again, you will need to adjust it back and forth (an installer does this until he/she learns the true direction in relation to the compass point). Even the elevation needs a little trial and error. The elevation marks on the dish are not always exact.
Finally, as far as which site is better than another, the only real problem I've found with antennaweb.org is that their information on which stations are broadcasting digitally is not always up to date. I'm not sure that any other site is any more accurate since the list changes daily.
I know, none of this will help you get NBC. But it may help your peace of mind.

 

[Vicki]

Thanks for your reply, greyghost. Unfortunately, it didn't actually help my peace of mind! May have made it worse, in fact...I just have difficulty buying the idea that installing and aiming a dish or antenna is "by guess and by golly", "trial and error", etc.

To my uninformed mind, it seems there's got to be more science and expertise involved, and I am determined to try to understand whatever science is involved and hope to monitor the level of expertise of my next installer. The elevation factor for the dish (seems to me) would be particularly important.

...But, could you please explain to me what the cookie monster has to do with the straight line to that one tower? I don't have kids or grandkids, so that was lost on me! Vicki

 

[rvsixer]

Vicki,

Most of the setup equipment you might use to set up dish and OTA antennae will not resolve to more than 1/2 of a degree. Therefore the azimuth/elevation numbers are helpful in capturing a signal on initial setup, after that its all tweaking the antennas using a signal level meter (the one in the VOOM box will suffice) to get it -spot on- for max signal.

Rob.

 

[Vicki]

Thanks Rob, I appreciate your input! From what I've read about some people's experiences, it seems possible to have an installer come up with an 85 on the VOOM signal level meter and say, "that's the best you're going to get."

My thinking is that in some of those cases, perhaps, the initial setup was not correctly calculated to begin with. Now, I love to cook, and I do understand that even the best recipes may require a certain amount of "fiddling" after you follow the instructions...so I just want to try to determine what the optimum starting point should be before the "fiddling" commences.

I guess my main questions remaining are:

Is the idea to deduct the elevation number from the azimuth number to get the best angle for my location?

Is the number described as “elevation” the same thing as the number for “Magnetic Declination” above?

If they are not the same, do I deduct the Magnetic Declination from the azimuth after I deduct the elevation?

Thanks again! Vicki

 

[TYORK]

Vicki,

you signal should be at aleast a 93 or better. i never get under a 93 .

tyork

 

[rvsixer]

I guess my main questions remaining are:

The pro's here did answer those questions nicely already .

And agree with them...if you don't need to know the how's and why's of magnetic variation etc, forget about them its simply not needed. Any initial signal is an "optimum" setting to start the tweaking from.

Best signal should be 95-98 with no weather to the satellite (and yes even on the west coast I get 96-97 with an 18" dish). EOT.

Best, Rob.

 

[Vicki]

OK...I'll give up trying to understand it! I was just hoping to save money for VOOM...time, frustration, and money for me, by trying to preclude any unnecessary additional service calls. (Please keep your fingers crossed for me for minimum roof tile breakage this time!) :river
Thanks to all for your help! Vicki

 

[rvsixer]

(Please keep your fingers crossed for me for minimum roof tile breakage this time!) :river

Don't put it on the roof .

Mines mounted on the side of the house under an eave. No snow build up to worry about, well protected from wind movement/damage, neighbors don't have to look at it, easy to tweak, and no worries about anyone falling off a ladder on my property (including me).

 

[greyghost]

I guess my main questions remaining are:



Is the idea to deduct the elevation number from the azimuth number to get the best angle for my location?

No. Elevation and azimuth are unrelated to each other.

Is the number described as “elevation” the same thing as the number for “Magnetic Declination” above?

No. The two are unrelated.

If they are not the same, do I deduct the Magnetic Declination from the azimuth after I deduct the elevation?

No. Nothing of the sort.

Cookie Monster reference: The Cookie Monster draws visible lines (numbers and letters) in the air with his finger.
Good luck with your installation. Let us know how it goes.

 

[Vicki]

rvsixer, I wouldn't put it on the roof if there's a way around it. I have pretty deep eaves on my house and lots of mature trees all around, not to mention the occasional hill, but I'll check into that possibility! Do you think that would work for the OTA too, in a deep-fringe area? Vicki

 

[Vicki]

greyghost, thanks for the reply again, and especially the Cookie Monster explanation! Sometimes I think I'm the only one in the world who chose not to have kids... Vicki

 

[jame_g]

Oh Vicki, please, no more posts like this. My head hurts. Work was over hours ago. Now I need a drink.

 

[Vicki]

Oh Vicky, please, no more posts like this. My head hurts. Work was over hours ago. Now I need a drink.

OK!! Mine, too!! Not yet, for me. Think I'll join you!

Is that better? Vicki

 

[tanis]

huh

Sounds like every one over complicates it the voom has all you need in the instalation wizard for fine tunning. two people and to way radios or a cell phone would make it easier

 

[Tony N]

Dish alignment is not at all scientific. This aint astrophysics! (It definitely is astrophysics to the guys that put the bird up there!) The DBS dishes use offset feeds which makes the dish look like it is pointing differently that the RAF beam actually pointing. The markings on the dish are crude, not in any way a precise measurement. They are intended only to get you in the ballpark, as are the Azimuth and Elevation numbers you find on websites, or via your receiver setup menu when you put in your zip code. DBS dishes have quite a wide beam width, so engineering accuracy is needless.

The Installer will simply point the dish approximately in the right direction, both azimuth and elevation. Usually they will get some signal right away. Then using a simple signal strength meter, they will rock the dish back and forth very slowly to peak the signal. Then do the same for the elevation. Then they might go back to azimuth and see if it needs a little more touch-up. Same for elevation. Lock it down and it is in business.

FORGET all about magnetic Variation, Compass Error and Declination. That stuff is needed when installing the larger steerable dishes that need more detailed alignment because they are trying to receive all the satellites in the arc from horizon to horizon, as well as having a much narrower beam width than DBS dishes.

Some receivers have an audible signal strength indicator. With that, you only need to set the receiver and a portable TV outside where you can hear it and rock the dish for the loudest, high pitch tone and you are peaked. That comes in handy if your dish got moved by wind or you have to relocate it.

Now about the Off-Air antenna. As was stated in other posts, those antennas have a very broad beam width. The main reason you would want to be picky about the direction would be to minimize ghosts. This is definitely heavy-duty trial and error as there is no possibility you can determine how signal is going to reflect off trees, buildings, steel structures etc. along the way or near the path to the TV stations. This will usually be somewhat of a compromise, because the direction that gets the clearest signal from one station may exhibit ghosts on others.

Elevation, thankfully, does not come into play here. Moving the antenna from side to side while someone watches the picture and shouts up at you as to when it is best is all that can be done.

There are rare cases when the best picture is had with the antenna pointed AWAY from the TV station. This can be the case when hills, tall buildings or other obstructions shadow you from the station. There are places in the Los Angeles area where huge refinery towers intervene between a location and the TV stations, blocking the signal, but a strong signal can be found reflecting off a refinery tank in an entirely different direction!

Hope this helps, rather than adds confusion.
Tony N

 

[rvsixer]

Dish alignment is not at all scientific. ...Hope this helps, rather than adds confusion.
Tony N

Nice complicated repeat of what's already been posted here .