Slimline "Firing pattern"

[houskamp]

Does anyone have any sort of a "engineering" type diagram of the pattern for a slimline 5lnb? sort of like an antenna pattern drawing.. would be nice to have one for identifing LOS problems.. Idealy a top view and side view would be nice :)

[litzdog911]

I've never seen a drawing like that. But it's pretty easy to find a location with line-of-sight to all of the DirecTV satellites .... see the link in my signature where you can use the moon & sun's location to "see" where the satellites are located.

[harsh]

sort of like an antenna pattern drawing.There is no real "pattern" as in the case of an OTA yagi or corner reflector. All you need is to look out the center of the dish at the elevation that is indicated on the scale on the base and you'll see where the 101 satellite is. It will be quite a bit above the vertical center line of the dish.

[hasan]

There is no real "pattern" as in the case of an OTA yagi or corner reflector. All you need is to look out the center of the dish at the elevation that is indicated on the scale on the base and you'll see where the 101 satellite is. It will be quite a bit above the vertical center line of the dish.

You are correct about the elevation being off from "line of site"...it will be about 20 to 25 degrees higher than the "physical" aiming point of the dish...this is due to the offset feed.

There is a very real "pattern", based on the geometry of the dish. If there weren't, it wouldn't work. The pattern is every bit as real and identifiable as that of a yagi or corner reflector...albeit quite a bit "tighter".

The pattern will be a single very narrow lobe for each LNB again, the angle of which, both azimuth and elevation is a direct function of the dish geometry and the placement of the LNB. In addition, there will be "side lobes" down at least 13 dB from the main lobe. Think of each lobe as a three dimensional cone being approximately 3 degrees wide at the half-power points, with minor lobes off each side, that are 13 dB or more down (and not useful) If that isn't a classic antenna pattern, then I don't know what is.

The pattern is well defined, replicable and available for viewing in any decent microwave antenna text. The math and diagrams for it are in any ARRL Antenna Handbook, as well as the Microwave Experimenter's Handbook (sic.)

For visualization purposes, thinking of the dish and feed optically will get you where you need to be, in terms of where it's pointing. The easiest to visualize is the pattern for the LNB/Satellite directly centered on the dish (left to right). In this case, the "lobe" or pattern is straight ahead, but elevated 20 degrees or more, in a tight, 3 dimensional "cone".

[houskamp]

I just posted this because 1:I have several trees south of me and am trying to figuire out which to trim (will try to take a pic tonight) 2: I have read several post trying to figuire out the same thng.. This dish is much harder to guess where it is actualy pointing..

[Smuuth]

I just posted this because 1:I have several trees south of me and am trying to figuire out which to trim (will try to take a pic tonight) 2: I have read several post trying to figuire out the same thng.. This dish is much harder to guess where it is actualy pointing..I used the link in litzdog911's signature on a night when the moon was going to be in the same position as the satellites at specific times. I posted pictures (http://www.dbstalk.com/showpost.php?p=926888&postcount=46) in that thread that were taken from behind the dish at the times the moon position synchronized with each satellite. I was pleasantly surprised that the satellites are considerably higher in the sky (as stated by others in this thread) than it would appear from looking at the dish itself.

[hasan]

I just posted this because 1:I have several trees south of me and am trying to figuire out which to trim (will try to take a pic tonight) 2: I have read several post trying to figuire out the same thng.. This dish is much harder to guess where it is actualy pointing..

You posted a VERY good question!

How far "left" and "right " of the center look angle do you need clearance at an elevation angle of about 20 to 25 degrees above the axis of the dish?

For this, you either need the experience of an installer, and of course, how far away the potential obstruction is.

There is an easier way, however. Find out the pointing info from your site to each of the birds you are interested in. That will be specified in azimuth and elevation. Get out your compass. Stand immediately behind or in front of your dish, in line with the dish and point yourself in the azimuth direction you have for a particular sat. Start with either 99 sat or 103 (the two extremes). Look up at an angle of about 38 degrees or so....do you see any obstruction?

Basically, find the az/el to the sat you are interested in, get out your compass for the azimuth, look up about 38 degrees (or whatever your elevation says) and see if you have obstructions.

[litzdog911]

I just posted this because 1:I have several trees south of me and am trying to figuire out which to trim (will try to take a pic tonight) 2: I have read several post trying to figuire out the same thng.. This dish is much harder to guess where it is actualy pointing..

If you private message your latitude & longitude to me, I'll run the numbers at the site in my signature link and let you know dates & times when the moon can help you locate the satellites. It's the easiest way to be 100% sure of the best location for your dish, or what trees need to be cut/trimmed.