Update Mods for Fortec 120cm dish.

[brentb636]

A couple months ago , we had a thread on Fortec dish modifications. This is my latest attempt, since I just put in a stiffer mast ( 2" Rigid conduit, filled with concrete) and re-aimed my dish. I still had lousy reception at the east and west, so I theorized that the lnb support need help. I strung a line from the top of the dish, to a spot on the lnbf arm, and adjusted it with an eyebolt ( turnbuckle would be better, but I didn't have one ) . The SQ increased by about 12 at both the true south and far west birds, so this is definitely the right track.

 

[Mr Tony]

odd that the LNB support needed.....well support

 

[brentb636]

Doesn't speak well for the engineering, having to "pull" it up slightly to optimize signal. Inspired by Post 26 of this old thread, http://www.satelliteguys.us/free-air-fta-discussion/160081-fortec-1-2m-dish-elevation-mod.html .

 

[turbosat]

Good job Brent, did it work better with a lighter lnbf, or did you just use that one from the start? Doesn't look like the design was tested much on that dish.

 

[brentb636]

The dish came with a smaller lnb, which I'll try eventually. I need to get a turnbuckle and some cable clamps to see if I can get a little more out of it. THEN, I'll get a C/Ku lnbf and play with mini-BUD .

 

[Anole]

alternatives:

Makes me want to find a 4' Primestar.
Perhaps the factory tour of the Prodelin plant will turn up an alternative dish.

 

[Tron]

Makes me want to find a 4' Primestar.

Too late, Anole, March is over now

But you never know, April might be the month of the 6' Prodelin!

 

[brentb636]

Makes me wish I'd driven over to Albion, and picked up a 4 ft Patriot to play with. They're only about 50 miles from me. They have a lot more weight, so motoring would be more of a challenge.

 

[TRG]

I've found that the plastic LNBF holders have too much flex in them sometimes. Especially with the heavier Invacom's. I wonder if you are actually compensating for something like that with your support mod .

 

[brentb636]

The cable support actually lifts the lnbf about 1 1/2" . I think that's too much for holder flex alone. I suspect that Fortec didn't bother to optimize the parts for this assembly.
On the positive side, this lightweight dish moves quickly from bird to bird, using the DG380 motor, and having "modded" the dish, I'm getting nice SQ numbers across the arc . I can hardly wait for it to snow tonight, so I can see how it handles the storm.

 

[Larry1]

Where does the large rectangular tube of the LNB support mount at the dish end? Is it just to the outside edge of the dish itself? Is the dish deformed without the new cable attached and you are just pulling the dish back into shape? that 3 point mount looks to be of heavy enough gauge to hold the LNBF without significant bending. What is bending when you tighen the cable?

 

[brentb636]

Has to be the edge of the dish, at the bottom. A single bolt holds the arm there. I theorize that the side support arms aren't doing their job very well, since not much can be expected from the bottom of dish attachment.

 

[Larry1]

Should try to see if you can email Fortec for a diagram with the measurements to the exact focal point (which will be slightly inside the feedhorn) from different points of the dish for you can make some measurements.

Like this that I have for my StarChoice/Winegard 1m dish
http://www.satelliteguys.us/free-air-fta-discussion/64324-dish-focal-distance.html#post550985
Also the crossed string test should help to point out any deformation/bending of the dish.

 

[brentb636]

Not a bad idea ! Stamps are cheap for email .

 

[Larry1]

That cat in your avatar looks like the cat my neighbour across my back fence has. It was standing off a fox on the weekend, then the cat shot off to his backyard. Must be the reason I have not seen any rabbits for quite some time.

 

[Othea]

fortec 1.2m

Strange. The lnbf support arm of your dish has a curve in it. All of the recent pictures that I have seen of that fortec dish show a straight lnbf support.

I'd be tempted to just remove the arm and step down on it until it straightens that curve just a tiny bit. It shouldn't take much since the side supports would then force the arm higher up.

I like your design.:up

 

[brentb636]

That cat in your avatar looks like the cat my neighbour across my back fence has. It was standing off a fox on the weekend, then the cat shot off to his backyard. Must be the reason I have not seen any rabbits for quite some time.

That male cat of ours ( now deceased) was a purebred Turkish Angora, lived his first years as a stud in a cattery. Then we got him, and he had a REAL life. He's a TIGER at heart.

 

[brentb636]

The new dishes have straight arms, but the diagram for this one definitely shows a curved arm. It's performing well right now, and I'm sure I can get more out of it in warm weather. Good thing this is a hobby, though. Most people wouldn't be interested in buying something just to modify the heck out of it.

 

[skysurfer]

Doesn't speak well for the engineering,

of course it's a poorly constructed dish. If I wasn't such a tightwad, I would have gotten the 120cm patriot.

But with 3 cheap mods as I and others discussed/did in the other thread, it performs great - probably as good as the patriot would and better than my 7.5' and 10' dishes on most ku-band signals - I'm guessing partially due to efficiency of the one piece compared to my others wtih multipanel biggies and partially that I use an invacom .3db integrated lnbf on it instead of a corotor II with the ku-band LNBs being a .7 db or so on each dish.

I did remove my fine elevation adjustment fixture, dish moved forward just a smidge so the bracket looks to be even poor on it - I put back on my fixture and I plan on leaving it on because it helps with support.

I got my due south sat right (I was using a satellite 2 deg off of due sat all that time) and it tracks the arc great with great signal strength from end to end. USALS sucks in some places by not recalculating things very precise in some areas of the arc, but that is a different topic...

edit: interesting slightly different take on the guy wire mod that I used - I went to teh base of the feedhorn arm/dish junction, I didn't put my lower attachment point halfway up the LNBF arm like the OP did. I took care of the LNB placement by changing the holes at each end of the LNBF support sidearms and the guy wire just brought the dish in a better parabolic shape (took out some of the minor "warpage"), it doesn't change the placement of the feedhorn looking into the dish.

even with a light LNBF, the dish isn't engineered right to put the feedhorn at the focal point. I would have still had to do the lnb sidearm support arms mod to get the LNBF in the right area if I had stuck with my $10 cheapie LNBF instead of getting a good invacom.