Tired of Winter Already - My Spring Project

[linuxman]

Ok, it's not even January yet, and I can't wait to get back on the roof for some more projects.

I have decided to build a T-180.

Everyone keeps talking about the T-90 and how well it works, so I am going to try and do one just a little bit bigger and hopefully a little better.

I am supposed to be getting this dish and mount right after the first of the year.

Edit: Ooops! Wrong pictures:





Fortunately, the arm will unbolt right at the bottom of the dish, so I can bring it and the mount into the warehouse to start work during the Winter months.

The dish is almost double the size of the T-90, so a little reverse engineering with measurements from some of you who already have the T-90s, and I think I can put one together and make it work.

If I can, it should give me ample room for LNBs every two degrees all the way across the arc. For me that would be probably 72W to 148W. If it would bring in all those, that would be great.

Might even be able to throw on a C/Ku combo in a couple of places.

So what do you think?

Is this doable?

Or am just having a grand pipe dream in the middle of Winter with 3-4" of snow in the forecast?

Fred

 

[Anole]

1st thoughts

Interesting idea.
We've got the math to locate some test-LNBs on it and see what the spacing would be for 2º.
Can you measure the actual focal length? We need that for the calculations.

Since it's not really a T-180, the LNBs will probably be located along an arc, unlike the T-90.
And unlike a real toroidal dish, there would probably be a lot more fall-off of signal toward the edges.
But those Ku LNBs right near the middle should melt down from their received signals! -

Since C-band on 6' dishes is crowding it anyway (or so I read), ya might put a C/Ku at the middle (center), but I wouldn't expect to have a lot of luck off the main focus point.

= SantAnole =

 

[linuxman]

Hey Anole,

We've got the math to locate some test-LNBs on it and see what the spacing would be for 2º.

The math would work, but I am planning on making the secondary reflector just like the T-90 has. It will have to be an inverted shield that follows the parabolic curve just like on the T-90.

Can you measure the actual focal length? We need that for the calculations.

I can't measure it until I get the dish in hand, but then the fun will start.

Since it's not really a T-180, the LNBs will probably be located along an arc, unlike the T-90.
And unlike a real toroidal dish, there would probably be a lot more fall-off of signal toward the edges.

I hope to make just like a T-90 with no fall-off in signal.

But those Ku LNBs right near the middle should melt down from their received signals! -

I am hoping they all melt the receiver meter.

Since C-band on 6' dishes is crowding it anyway (or so I read), ya might put a C/Ku at the middle (center), but I wouldn't expect to have a lot of luck off the main focus point.

Agreed!

The C/Ku idea will be an after-thought if everything else goes according to plan.

 

[mikekohl]

There is no doubt that you'll have a fire hazard from those smokin' signals at the center of the antenna's focal point, but my experience on another 1.8 m
offset is not to expect miracles any more than 20 degrees left or right of center, where you will experience a rapid drop off of signal level, due to
the greater directivity (narrower beamwidth) of a larger dish.
Let us know how you do.

 

[linuxman]

Hey Mike,

There is no doubt that you'll have a fire hazard from those smokin' signals at the center of the antenna's focal point,

When I first started reading your reply I thought you were going to say that I had smoke signals from smoking something.

Thanks for the information.

At least it will be a fun project and provide something for me to do inside while I am waiting for the weather to warm up.

I have been thinking of ideas of what to make the secondary reflector out of, and have some things in mind that I have seen in salvage yards etc. For instance, I have seen a lot of large thin wall tubing laying around that could be cut in half, and then heated and shaped for one idea.

Another would be to construct an aluminum frame and put fine mesh wiring on it for the surface, but whatever it is, the surface needs to be accurate.

Oh well, I am sure the collective minds here can come up with some ideas.

 

[turbosat]

How do you get around the oddball skew of AMC1 though?
lol

 

[linuxman]

How do you get around the oddball skew of AMC1 though?

I don't know at this point. I haven't ever tuned in a T-90 type dish, but I would think the individual LNBFs could be skewed individually.

I will have to cross that bridge when I get to it.

 

[voomvoom]

How do you get around the oddball skew of AMC1 though?
lol

Same as with a T90, you adjust/skew the lnbf for best picture.

Al

 

[Anole]

Oh, a subreflector, eh?

Well, that's a whole 'nother ball o' wax...

You will probably want to get your hands (and calipers) on a T-90 for inspiration.
Some drawings wouldn't hurt either.

If ya pull it off to where an average reptile could build one without a machine shop, you'll go down in the annals as a real hero.
I'll try to scale one of those pictures and guess the approx focal length...

I think I'd be happy with a big LNB-mounting track across the front, built in the traditional way.
edit: Kinda like what Netbuilder has shown on his sat site.
... or the multi-feed examples on the Global-CM site.
(and it makes more sense to me, to skew that track-way, based on your location)

 

[linuxman]

Yeah Anole,

I thought about trying the traditional multi-LNBf route like shown in the links.

As Mike Kohl said above, with the bigger dish that may be the only way it would work, and he is correct about the 20 degrees either side of center.

If I could get 30 degrees either side of center with a sub-reflector that would allow for 72W - 121W, maybe even get 123W squeezed in with 91W or 93W as my center. Then I could put White Springs and 148W on a primestar with good signal without any problem. I am going to give 148W a shot on my existing 123W-129W dish as soon as I can get my hands on an un-committed diseqc switch and some warmer days. I don't have the setup for any more LNBFs until then.

Either way it works out is fine with me, but I think it will be fun to try both ways.

 

[Wescopc]

The T-90 is not oval like a single reflector dish. I think there is unique "ray tracing" involved that would require a computer modeling to get a set of reflectors that would work together. I know this sounds like sour grapes - just thinking of a spun aluminum reflector that didn't work well. I have a lot of respect for these T-90 dish designers.
Bob

 

[Tron]

Wescopc is correct. The T-90 has, for lack of a better description, a sort of rounded triangular shape to it. The bottom of the main reflector is wider than the top of it.

 

[linuxman]

Hey Bob,

I know this sounds like sour grapes - just thinking of a spun aluminum reflector that didn't work well.

It's not sour grapes at all, but a realistic understanding of how a real T-90 is made. I haven't ever seen one in person, so I really don't know what the reflector is shaped like.

After thinking about it for a day or two, I'll probably start out with the conventional multi-lnbf approach as the links in Anole's reply above and see how many degrees I can get with that.

I would just like to maximise the use of the dish in the best way possible.

I don't mind putting up more dishes. I have two Primestar 84Es in the warehouse now waiting for a spot to be used.

If I can get 20 degrees either side of center from 91W as my center with great signal quality, that would be pretty awesome for a single dish, especially if I can put an LNBf for every satellite in that 40 degree range.

That would be an LNBf for 72, 74, 79, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103, 107.3, 111.1W, that's a lot of LNBfs one one dish. That's assuming of course that the size of the dish will allow for 2 degree spacing of the LNBFs.

I could then fill in the rest with smaller multi-lnb dishes.

I read here somewhere that someone was hitting 119W, 123W, 129W, and 148W on an 84e with multi-lnbfs. I already have a dish with 123 and 129 on it. Maybe I'll just add to that one for the far West.

I anticipate having a lot of fun building this in the warehouse and putting it up this spring.

 

[linuxman]

Thanks Tron,

The T-90 has, for lack of a better description, a sort of rounded triangular shape to it. The bottom of the main reflector is wider than the top of it.

From the pictures, it is hard to tell what the true shape is, at least for these aging eyes.

 

[scottc98]

Fred,

If you are really serious in persuing with this project, I have a spare T-90 in the garage not in use ( only thing missing are the lnb holders and the mount). Be happy to let you borrow it as long as I get it back I'm not sure when I am going to put it up but it wont be until atleast march.

You could always make a sadoun run and pick it up
I'm 5 min away

Just a thought

Scott

 

[linuxman]

Hey thanks Scott,

I appreciate the thought, but a 5 min run for you would be a 15 hour run for me.

Besides, I might like it and then I would have to buy one. Perish the thought!

Who knows, I might end up buying one before the summer is over anyway, and give this setup to the family for their tv.

The T-90 concept is certainly intriguing to me.

With my current setup, I can switch from White Springs, to G10, to 97W, to 91W C-Band, to 87W, to 30W, and check out what's on without ever having to move the Birdview because most of the time it is left at 91W on the C-Band side.

It is very nice not having to wait on moving the dish. It will be great to have all of Ku on switches.

Then I might have to put up some stationary C-Band dishes to expand the switch idea.

I only have 5 more BUDS in the warehouse that I could put up.

Surely I would be able to tune them in on individual satellites for satisfactory signal quality to suit me.

 

[Anole]

I read here somewhere that someone was hitting 119W, 123W, 129W, and 148W on an 84e with multi-lnbfs.

Netbuilder has 110W, 119W, and 148W, with G10R 123º at the focal point, on a DirecWay Dish of 39X23 inches.
Based on what I've read, that size dish will get ya something linear at the center of the focus, but it's not optimal.
However, the circular birds are receivable on 18-20" dishes, so even way off center on a 39x23, they're still gettin' plenty.

It's confusing and misleading to mix circular satellite locations with linear ones, when bragging how far a span one can get on a dish.

I already have a dish with 123 and 129 on it. Maybe I'll just add to that one for the far West.

If you have a subscription or just want to see what's FTE, I'd think 119º would be easy, and probably 110º.
Not so sure about 148º, but based on recent reports, I'd give ya odds.

 

[linuxman]

Hey Anole,

It's confusing and misleading to mix circular satellite locations with linear ones, when bragging how far a span one can get on a dish.

That's for sure!

If you have a subscription or just want to see what's FTE, I'd think 119º would be easy, and probably 110º.
Not so sure about 148º, but based on recent reports, I'd give ya odds.

I don't know either, but it won't hurt to try.

Maybe put 129W as the center and go that route. That's 20 degrees to the West for a Circular, 7 degrees East for a Linear (G10) which has pretty good signal now. and a total 20 degrees for two Circulars on the East side.

I think I can get 148 tuned in all on the same dish. There isn't much there, but it doesn't hurt to have access. Be prepared is my motto. (Maybe that was the Boy Scouts) Hmmm!

I can see now that I am going to have to start looking for some extremely inexpensive standard Linear LNBFs.