Need help with Primestar 84e multi-feed

[brada]

I set up 84e to get my Globecast channels, but I want to put another LNBf to get AMC3. G25 LNB is in the center, and I tried to use MJFlash formula to find a place for AMC3 LNBf, but had no luck: no signal I got at all
This is how I think it should be calculated:
Azimuth/Elevation for 97W: 142.6/39.6
Azimuth/El. for 87W: 131/33.6
Distance between LNBf and center of the dish (between 4 bolts): 54.5 cm

Horizontal offset should be then: 545 x sin (142.6 - 131) = 109mm
Vertical offset: 545 x sin (39.6 - 33.6) = 57mm

I tried my best to put second LNB in that spot, but had no signal!
I think, my problem is that the whole dish is tilted (skewed with the scale on the back).
Should I set it straight? And just turn LNBf?
If someone has any thoughts, please, let me know, I don't beleive, it cannot be done. In the picture below, I put a circle where I had the second LNBf for 87W:

 

[turbosat]

I read someplace else that a dish that shape needs to be skewed, even if its not motorized, in order to get the best efficiency from it. (Sounds logical to me) The question then would be how to get a happy medium between the needed skew for 87, and what is needed for 97. And then finding the right spot for the 87lnb to focus on. I can't recall reading where anyone got 2 sats 10degrees apart on a single dish, it must've been done by somebody....

 

[voomvoom]

I think if you have G25/IA5/T5 in the center, you are maybe stretching it a little. 10 degrees may be too far from the center for that dish. If you put 91.0w or 93.0w in the center and put an extra lnbf on each side, I think you would fair better. Just my opinion.

Al

 

[Keith Brannen]

I set up 84e to get my Globecast channels, but I want to put another LNBf to get AMC3. G25 LNB is in the center, and I tried to use MJFlash formula to find a place for AMC3 LNBf, but had no luck: no signal I got at all
This is how I think it should be calculated:
Azimuth/Elevation for 97W: 142.6/39.6
Azimuth/El. for 87W: 131/33.6
Distance between LNBf and center of the dish (between 4 bolts): 54.5 cm

Horizontal offset should be then: 545 x sin (142.6 - 131) = 109mm
Vertical offset: 545 x sin (39.6 - 33.6) = 57mm

I tried my best to put second LNB in that spot, but had no signal!
I think, my problem is that the whole dish is tilted (skewed with the scale on the back).
Should I set it straight? And just turn LNBf?
If someone has any thoughts, please, let me know, I don't beleive, it cannot be done. In the picture below, I put a circle where I had the second LNBf for 87W:

While 10 degrees off-centre will have some loss of signal quality, you should be able to get AMC3 on the dish. I currently have (see signature below) AMC9 10 degrees off-centre on a 60e dish (which is good enough for what news feeds show up). At one time I had AMC4 on my Star Choice dish (60e), again 10 degrees off-centre. Signals were fairly good, got all channels viewable.

I did, at one time, have G25 (97) and AMC3 (87) on one dish (80cm) and I detailed some of my experiences in this post:
http://www.satelliteguys.us/918723-post35.html
and the whole thread:
http://www.satelliteguys.us/free-ai...123w-129w-1-meter-primestar-4.html#post918723

When you do lock on to AMC3, and if the signals are not strong enough, then you migh want to move both LNBs off-centre, so you might want to check this thread:
http://www.satelliteguys.us/free-air-fta-discussion/99108-87w-97w-primestar-84e-multi-lnbf.html

In regard to your specific questions:
Keep the dish skewed for G25 (97). Your bracket for the AMC3 LNB should run parallel to the tilt of the dish, the difference in vertical off-set from that parallel line will be very minor. See this thread for some explanation for skew (page 2), etc.:
http://www.satelliteguys.us/free-air-fta-discussion/101134-91w-97w-123w-75e-dish.html

Your horizontal offset seems about right, but should be used only as a starting point, I have found the "sweet spot" can vary in distance from off-centre for LNBs with the same degree difference (as well as angle towards the dish). I always do a hand-held approach to zero in roughly where the LNB should be.

Good luck!

 

[Anole]

all things are relative

I didn't check your math, but if you read all the info in the MJflash thread, (and I went over it in Linuxman vs the 123/129 thread), you should be good.

What that calculates, is the location of the 2nd LNB, all right, but . . .
. . . relative to the earth, not to the skew of the dish.

So, if it comes out with 2 inches east/west of your existing LNB, move the new LNB 2 inches left or right, not diagonally.
Ignore the skew of the dish for locating the new LNB.
And as KB says above, that's just a starting point.

 

[brada]

...
What that calculates, is the location of the 2nd LNB, all right, but . . .
. . . relative to the earth, not to the skew of the dish....
And as KB says above, that's just a starting point.

Yes, that I think, my mistake was: I measured those mm's from that metal LNB bar, which is parallel to the dish skew. I will try to do it one more time on weekend. And yes, Keith's signature was a first thing for me to confirm, that this is possible to get sats 10 degrees apart (while one is in the center) even with STarChoice 60e dish, which I think is a smaller brother of my 84e.
Thank you everyone, I will get back with results

 

[brada]

In less than half a year, I finally got some result: a signal from 89W though, not from 87W. I got 41-49% "signal quality" from 11955 V transponder (with ABC_Now), and it's viewable!
But I feel, something is wrong, because the second LNB gets the signal not from the center of the dish as I expected, but from its "left wing":


Is it normal direction, or it's possible to aim dish better?
The central LNBf gets a good signal from G25-97W.
I will appreciate any advice

 

[Mr Tony]

Looks like the LNB's are even with each other. Unless the elevation for 97 & 87 (or 89) is the same its going to be difficult. Where I am in Minneapolis 97 & 87 are almost the same elevation (93 is my true south) so it would work but in California (according to your location) the elevation is different (and dramatic since from 97 to 87 it drops a fair amount)

You'd have to bend that bar a little bit

 

[Keith Brannen]

But I feel, something is wrong, because the second LNB gets the signal not from the center of the dish as I expected, but from its "left wing":

Is it normal direction, or it's possible to aim dish better?
The central LNBf gets a good signal from G25-97W.
I will appreciate any advice

It does get the signal from the "left wing" but the LNB shouldn't be angled so much to the outer rim of the dish, and suspect you are only get part of the signal.

I think part of the problem is that the LNB is too far forward in relation to the G25 LNB, it should be more parallel to it.

Below are photos of my 60e dish and LNBs. The LNBs, from left to right on the photo from in front of the dish are: AMC9 (83) (about 3 3/4 inches off centre), left side of the dual Star Choice LNB at G28 (89) (not in use, as I have it as the centre LNB on the dish behind it), right hand side of the dual Star Choice LNB at G26 (93), and G16 (99) (about 2 1/8 inches off centre).

(Note: Your distances from the centre on your 84e would be slightly larger if you had the same setup.)

The side photo shows how the LNBs are basically parallel to each other.

Try moving the LNB back, and angling it more parallel to the dish and other LNB (your distance from the G25 LNB will probably change).