Two LNBF alignment question

[tvropro]

Let's throw this out and see if I can get some feedback. I currently am running my ADTH 84cm with a dual LNBF setup on AMC4 and G-19. I have G-19 at boresight and AMC-4 as an offset. Im looking for a better signal out of AMC-4 and can gain 15 Q points if boresighted at that bird. Seems though G-19 looses more though if I go that route then AMC-4 does now.

My question is you guys that are doing a dual LNBF on those birds which bird is your boresight? Also I was thinking about pointing in between the two and seeing if I could add gain that way. Possibly skewing the dish came to mind too.

Feedback Please.... Thanks.

 

[Mr Tony]

When I had mine setup that way 97 was the dead on and 101 was the offset

101 in most cases (couple TP"s are the exception) is much stronger than 97. I lost too much signal on 97W as the offset

 

[tvropro]

I was thinking of fabricating a holder that would not be at boresight on either bird. Kinda in between each, then point the dish halfway between at 99 and then each bird will see more of the dish. What's your take Ice?

 

[Mr Tony]

Thats what Glorystar does with their 2 LNB bracket. Its 2 degrees offset for both

 

[tvropro]

Thats what Glorystar does with their 2 LNB bracket. Its 2 degrees offset for both

Thats what I want to do. I spoke with my neighbor friend today (the one who designed the base for the W5 project) and told him what I want to do. We looked at a couple designs on the net. He said he had a pretty good idea on what I want and said he will ponder a design. This guy is good and has the smarts and tools to fabricate stuff out of whatever.

On the Glorystar bracket are the LNBF cradles right in line? I was thinking of having adjustment left to right for each cradle. Then have the whole cradle twist to adjust for any skew between the two birds.

My goal is to increase AMC-4 HTN mux signal and loose the least amount on G-19.

 

[Mr Tony]

On the Glorystar bracket are the LNBF cradles right in line? I was thinking of having adjustment left to right for each cradle. Then have the whole cradle twist to adjust for any skew between the two birds.

correct. There is a skew adjustment on the holder and then each LNB can skew or be pushed in/out

Free Christian Satellite Television - No Monthly Fees from Glorystar Christian Satellite!

 

[Wescopc]

Because you are East of 99W the Glory Star bracket will place 97W closer to bore site. You can check on it by going here:
GeoSatFinder - Satellite Finder Calculator - Satellite AV
You will see that the rotation is + when you choose 99W (half way between 101 and 97W)
Bob

 

[tvropro]

This is what I see in my head and want to build

 

[Mr Tony]

that looks just like the Satelliteav/glorystar setup

 

[tvropro]

that looks just like the Satelliteav/glorystar setup

Yeah the only difference is I want to make the lnbf's able to slide closer together and farther apart. This would probably help my dish since it's an elliptical. Plus it gives me more to play with down the road if I decide to spread the spacing to 6 or 8 degrees between birds.

My current setup works but the HTN mux on AMC-4 seems to go from a high of 60 to below threshold quite a bit. When I was aligning it I was getting 45 from it with offset 4 deg off boresight. If I boresighted the dish it went to 60. Tonight I was getting 14 or so I'm hoping with the mod I can at least hold 30 when there signal drops down. I tried having 101 at center but 97 went from 60 to 30 so I figure that was a worse situation.

In theory at 2 deg off center I should effectively maximize each bird as much as possible being offset from boresight.

All in all though Ice it's a good learning experience and how multiple lnbs work. Also what needs to be done to maximize what you have.

 

[SatelliteAV]

We have a sample of this exact concept. The design is acceptable for two satellite (LNBFs) in close proximity (I.E. 4 degrees) or on a dish designed for reflecting multiple satellites into multiple LNBF positions. A vertical fine tuning adjustment is necessary to optimize feedhorn positioning as the distances increase as skewing the LNBF mount will not place the feedhorns in the optimum position if placed too far outside the prime focus position. The convergence points do not remain linear on a typical offset reflector designed for a single convergence point.

Wow.... That was a mouthful!!!

 

[tvropro]

Brian, What would be the maximum spread between birds be on a ADTH eliptical dish? I figure about 8 degrees. After that there would be too much loss.

 

[SatelliteAV]

Never worked with that dish, but with a FD of .7 and the extreme height to width ratio I would think that it would not be a good candidate for a skewing LNBF bracket. It would be a tough dish get a wide spread of birds. Won't speculate on the performance of reception on multiple satellites or the limits for spacing.

 

[tvropro]

Isn't wider than taller better for multiple birds? The ADTH is that, 29.53' high x 34.25' wide. What I've been told that taller and narrower is better for adjacent satellite rejection. It seems the pie services use wider and shorter dishes for multiple birds. I would think that will hold true with fss ku also, any take?

 

[Anole]

Elliptical dishes (wide) like the DirecWay used for internet access, are wide to help suppress adjacent satellite interference.
(acts like a big round dish)
With such a dramatically elliptical dish, you'd need to skew the entire dish for best performance.

I didn't realize the ADTH was other than round.
Brian may have a good point about the dish performance.
Certainly so for far LNB spacing.
If all else fails, you might try skewing the entire dish.

You could calculate horizontal spacing and vertical spacing for your two LNBs.
It helps if the two satellites you are shooting for are not way low to your east or west horizon.

I have G-19 at boresight and AMC-4 as an offset.

edit: I re-read your original post.
Just measure the horizontal and vertical LNB spacing NOW, and use that as a starting point for your offset bracket.
If you'd post those numbers, it might prove educational.

 

[tvropro]

I took some pictures of the current setup. The last one I put some measurements on. Okay Sat Guys Guru's give input

I only want to do 4 degrees right now.

Edit added location lat & long plus sat specs for me, don't know if that helps.

 

[Keith Brannen]

Isn't wider than taller better for multiple birds? The ADTH is that, 29.53' high x 34.25' wide. What I've been told that taller and narrower is better for adjacent satellite rejection. It seems the pie services use wider and shorter dishes for multiple birds. I would think that will hold true with fss ku also, any take?

It has been my experience that elliptical dishes (mine are all skewable) are better at both separation of satellites, and at maintaining signal quality the further off centre you go than "round" dishes.

If you remember (which I'm sure you do, considering our many conversations!), during the interference that the Equity (RIP) channels were experiencing from AMC21 (125) , my only solution was to point my 75e at G18 (123). Not only was the interference gone, but the signal quality on all transponders was equivalent to what I had been getting on my 80cm, and the G18 LNB was the 4 degree off-centre LNB!

Currently, my 75e has AMC9 (83) at boresight, with AMC6 (72) at 11 degrees off-centre. AMC6 is very strong here, and I am getting a stronger signal now, than when I had the LNB on a 80cm at roughly the same 11 degrees off-centre.

The Star Choice 75e is 35 3/4 wide by 26 1/2 high, so is more elliptical than your dish, and, as I said, is skewable.

It looks like your dish is on a pole (can't really tell from the photos), which would appear to make it unskewable, but if you can skew it at all it would be beneficial. If it is on a universal mount, then it is possible!

 

[tvropro]

The dish isn't skewable now. Im sure I could adapt something if really needed. I think at 4 degrees though that it shouldn't be a large concern. Im mostly looking to optimize AMC-4 while loosing very little on G19.

In theory placing each lnb at 2 deg off boresight (and point b/s at 99) should hopefully achieve this. I figured being elliptical would be a benefit here.

 

[Keith Brannen]

The dish isn't skewable now. Im sure I could adapt something if really needed. I think at 4 degrees though that it shouldn't be a large concern. Im mostly looking to optimize AMC-4 while loosing very little on G19.

In theory placing each lnb at 2 deg off boresight (and point b/s at 99) should hopefully achieve this. I figured being elliptical would be a benefit here.

Only thing I was concerned about as far as skew goes, is that you are already giving up some of the benefits of the elliptical dish due to the LNB skews of 10 and 14 degrees.

Currently, I have one dish in a similar situation as what you want to do, where there is no LNB on the boresight. As well, I had the same dish in another set of LNB configurations without a boresight LNB. In both cases, the closest LNB was about 3 degrees off centre (the width of the LNB holder).

Now, my LNB arm is flat (unlikely your rounded one) so what I did may not work well for you (depending on how you can mount a bracket to hold the LNBs). First off, my dish was peaked on boresight at the satellite that would be closest to the arm (3 degrees off-centre). Then I removed the LNB and mounted it on the bracket so that it was against the LNB arm and parallel in height to where the LNB had been. Then I repointed the dish, but did not change the elevation. This way, I believe, the LNB is seeing slightly more of the dish than if I had adjusted the elevation to point at an imaginary satellite 3 degrees off-centre, and lowered or raised the LNB.

If you can do a similar thing on your dish, then I would suggest using G19 (97) to do the pointing so that when moved off-centre it sees as much of the dish as possible, which could minimise some of the loss of being moved off-centre.

 

[tvropro]

I read your alignment trick. Interesting concept I'll give it a try. My neighbor friend stopped by today to get some angles and dimensions needed to fab the LNBF holder. I leave that part in his hands since he's a retired machinist and can do some wild stuff. Once that's put together I can slap it up there and see what happens.

BTW Keith does your HTN channels on AMC-4 get weak at night allot? I wonder if it's weather related at the uplink since it's clear here. Wonder where the uplink is too?