Focal finder for scalar ring on dish

[stogie5150]

I am looking in the C-band FAQ and it see a refernece to a focal finder for centering the scalar ring/LNB on a cband dish. I am having a heckuva time locking some TP's with my new Geosat Pro Dual LNB that I never had with my old co-rotor/25 degree LNB setup. When I installed the LNB I just put the 'ol calibrated eyeball on it and tightened it. Anyone ever made a homebrew focal finder? See below for what I am talking about.

 

[gabshere]

I saw one on ebay a while back ..... ok heres something that will also help
when you place several strings on the dish to get the focal distance and to make sure the dish has proper shape. this method will also show you the center of the dish so you should be able to take a small straight edge item and should be able to get the center point at the feedhorn.

i won't say all but i really thing that most dishes when installed were installed inproperly or poorly .....( ok i will correct the poorly statement , older dishes were set up for analog signal which was more forgiving than digital is, so poorly is not the best word for this statement) they were set to the best for signal they were receiving at the time , maybe for c-band only or whatever. plus after so many years being installed some dishes have slight damage or even sag so it would be best to re-tune / peak the feedhorn.


another thing to consider is this and i got this from Linuxman , although you have great signal from on satellite and poor signal from another at the other end of the arc , your best signal for both might be a comprimise between the two (and this could be a loss in signal quality for both signals) so find youe setup satellite (usually due south sat) then find a east satellite and then west satellite and peak between the three to gain the best signal for tha arc (across the arc) (i hope i got the right Linuxman).

 

[SatelliteAV]

I use a 8" level with a built in LASER pointer. Using the concept of the LASER pointer feedhorn insert that was sold years ago, simply lay the level across the throat of the feedhorn and center the LASER pointer.

 

[gabshere]

Brian
thats a super idea , i will try that when i line up my next dishes

 

[linuxman]

Hi Stogie,

I read that last year when I first started out in this hobby and no one makes them any more.

I have tried several methods since then. I made one like the picture using a cheap laser pen and hot glued it to a spare cap that I had. Course that only lasted a short while and the pen died.

I also tried a piece of all thread with a piece of flat steel with a hole drilled through the center and hold the flat piece across the wave-guide. It was too heavy to be of any real use.

What I am using now is a foot long piece of 1" flat aluminum about 1/8" thick. I place that on the wave-guide exterior to provide a flat surface to put a laser level on to shoot to the center of the dish. I check it at the top, bottom, east, and west points of the dish for center.

I do all that after measuring from the outside rim for proper distance.

Here are pictures of what I do.





I put a small piece of tape over the laser eye to form a more precise dot on the dish.

Edit: Well I see that others have replied since I started this reply before church this morning. I like SatelliteAV's idea and will see if I can find one of those critters. And yes George, you are correct.

Fred

 

[stogie5150]

Well, I am not sure I understand all of that...

But I trust its all good information....

I have a laser pen...but I would have to figure out a way to mount it to something to shoot through the scalar ring. I have all kinds of machinst's scales up to 2 feet...I guess I could lay one acrooss the scalar ring and shoot a beam that way...Looks like I have some more homework to do.....

Thanks Yall...:up

 

[linuxman]

but I would have to figure out a way to mount it to something to shoot through the scalar ring.

The scalar ring is important and should be parallel with the base plate of the dish, the most critical part is having the wave-guide pointing at the center.

The little set screw that comes with the co-rotor or polarotor sometimes allows the center piece (wave-guide) to get cocked and difficult to get straight. That is the part that needs to point directly to the center.

Fred

 

[GreatFTA]

If I can find a laser level that shoot a laser beam up as well as across, then I would take a Chapperal blue cap that fit over the mouth of the feedhorn and center it on the cap and have it to stay on. That way when I get ready to finetune the feedhorn as far as centering it to the middle of the dish I would pop on the cap with the laser and go for it. I hope this idea works.
Does that laser level Linuxman shown in the pixs shoot a laser at a 90 degree angle as well?

 

[linuxman]

Hey MrFTAMan,

Does that laser level Linuxman shown in the pixs shoot a laser at a 90 degree angle as well?

The laser level in the picture above does not shoot at 90 degrees. I wish it did.

Fred

 

[stogie5150]

Since the feed I am using has separate scalar/waveguide why couldn't I take a pvc pipe cap that is very close to the correct size and cement a laser pointer in the center of the cap, take the waveguide out,slap the pipe cap on the sky-side of the scalar ring and align it from there?

 

[linuxman]

take the waveguide out,slap the pipe cap on the sky-side of the scalar ring and align it from there?

Hey Stogie,

That would work, but all you would be aligning is the PVC cap/insert. You would have no guarantee that when you took the PVC out and put the wave-guide in that it is aligned properly.

Fred

 

[stogie5150]

Hey Stogie,

That would work, but all you would be aligning is the PVC cap/insert. You would have no guarantee that when you took the PVC out and put the wave-guide in that it is aligned properly.

Fred

Wouldn't that center the scalar ring to the dish though? If I made very sure that the cap with the pointer is centered exactly with scalar ring wouldn't that work? How would it not? Then once I got the scalar ring centered I can put the waveguide in and adjust for the focal length.

Remember I have a two piece lnb/scalar ring assembly.

 

[lumpkin666]

Wouldn't that center the scalar ring to the dish though? If I made very sure that the cap with the pointer is centered exactly with scalar ring wouldn't that work? How would it not? Then once I got the scalar ring centered I can put the waveguide in and adjust for the focal length.

Remember I have a two piece lnb/scalar ring assembly.

Some of those lnb's don't fit all that snugly in the scalar ring (i.e. the BSC621 stuff). The biggest problem I have with them is not getting the scalar ring straight on, but getting the lnbf to sit precisely centered in the scalar (especially since they have only one bolt to tighten them down, and about 1/4 inch play in the whole mechanism).

 

[linuxman]

Wouldn't that center the scalar ring to the dish though?

Yes, it would center the scalar ring.

Then once I got the scalar ring centered I can put the waveguide in and adjust for the focal length.

Remember I have a two piece lnb/scalar ring assembly.

That is my whole point.

You can have the scalar ring centered, but after removing the PVC piece and inserting the wave-guide, it could still be cocked when you tighten down the set screw, and therefore still won't point to the center of the dish. That's why they made the tool in your first post in the beginning. Because it slipped right onto the wave-guide to center it and the scalar ring at the same time.

Fred

 

[stogie5150]

OKAY! Thanks to your perserverance I THINK finally understand. Thank You.

Once I have the ring centered with the dish the issue will be to get the waveguide square (actually perpendicular) with the ring,therefore with the dish, correct?

BUT, and there's always a BUT, IF I got the scalar ring centered couldn't I just adjust the waveguide for the best signal, then check it on various satellites? That's basically what I did when I set it up, and some sats have better signal than others for sure....

One more thing, how CLOSE do I have to be? .125 inch? .100 inch? There has to be some leeway otherwise they never would work 100 percent.

Yes, it would center the scalar ring.


That is my whole point.

You can have the scalar ring centered, but after removing the PVC piece and inserting the wave-guide, it could still be cocked when you tighten down the set screw, and therefore still won't point to the center of the dish. That's why they made the tool in your first post in the beginning. Because it slipped right onto the wave-guide to center it and the scalar ring at the same time.

Fred

 

[gabshere]

That's basically what I did when I set it up, and some sats have better signal than others for sure....

One more thing, how CLOSE do I have to be? .125 inch? .100 inch? There has to be some leeway otherwise they never would work 100 percent.

i suspect this is why my ku is off on some satellites and right on on others. i will have to gain that .125 inch and find a better happy medium for the best ku across the arc .... well maybe that will be this weekends project i do have a laser level

 

[linuxman]

Once I have the ring centered with the dish the issue will be to get the waveguide square (actually perpendicular) with the ring,therefore with the dish, correct?

BUT, and there's always a BUT, IF I got the scalar ring centered couldn't I just adjust the waveguide for the best signal, then check it on various satellites? That's basically what I did when I set it up, and some sats have better signal than others for sure....

I think that is where everyone makes the biggest mistake in the final peaking of the dish.

The F/D ratio is a set parameter, once you have the F/D ratio set, then make sure the wave-guide is centered on the dish and tighten down the set screw.

After that, the only in and out adjustment available to you is with the entire assembly. You don't loosen the wave-guide and just move it in and out. You loosen the bolts on the scalar ring and move it in and out for best signal. After such loosening and adjustment, you again have to make certain all is centered again.

From what I have read, that is the proper method for adjustment, and it has worked well for my existing dishes.

Fred

 

[gabshere]

well i will check it all this weekend .... fred that sound like a plan i will reset my feedhorn assembly and start again.
i first have to straighten out one of my support arms that got bent .....

will have to check to see how much movement my support arms will allow for adjusting the scaler.

thanks

 

[stogie5150]

I think that is where everyone makes the biggest mistake in the final peaking of the dish.

The F/D ratio is a set parameter, once you have the F/D ratio set, then make sure the wave-guide is centered on the dish and tighten down the set screw.

After that, the only in and out adjustment available to you is with the entire assembly. You don't loosen the wave-guide and just move it in and out. You loosen the bolts on the scalar ring and move it in and out for best signal. After such loosening and adjustment, you again have to make certain all is centered again.

From what I have read, that is the proper method for adjustment, and it has worked well for my existing dishes.

Fred

Well that will be neigh impossible for me, there is NO in and out adjustment of the whole assembly. The only way you could possibly adjust it is away from the dish with washers as spacers. Or bend the support legs, and that introduces all kinds of possibilities for errors.

When I inserted the waveguide there defintely WAS a sweet spot for signal, and that's where it is, regardless of the distance printed on the side of the waveguide.

I am going to go out this morning and mess with it a bit...

 

[linuxman]

Hey Stogie,

I understand about the problems associated with adjusting the entire feed-horn in and out. I did have to put fender washers between the support arms and the dish to move the assembly out on the SAMI dish. There were no other adjustments. I am also going to make a special ring to allow for more adjustment on the Pinnacle dish if I can ever get the spun aluminum dish up. Thankfully the welder came by last night and picked up the steel for that mount. Should have it back by this week-end.

The Birdview was a non-adjustable assembly too, but when I put all of that together and set the F/D ratio, BAM! the Focal Distance was already set as close as I would ever get it.

Generally, if the dish is made like that, what the factory has will be close. The place to start is with the correct Focal Distance, or Focal Length as it is sometimes called. That is the distance between the center of the dish to 1/4" inside the wave-guide. The Focal Distance can be found with the factory specs or calculated with an on-line calculator.

The problem is that most of these dishes were manufactured for C-Band. C-Band is much more forgiving. Ku on the other hand is not.

Most people are happy with close. Unfortunately, I am not one of them. Part of the problem with our society is that we are "Addicted To Mediocrity". I literally spend weeks of spare time peaking my dishes. Why? I want every last percentage of Signal Quality I can get out of the dish. But that's just me. That is one of the things I love about this hobby. Always trying to get a better signal. "Every little bit helps."

Other people solve the problem by putting on expensive LNBs to compensate for lack of alignment. That's the second part of this hobby I love so much. Making everything work well with the least amount of money spent as possible.

I hope all of this helps you guys fine-tune your dishes.

Fred