Best brand dish to retain shape in tropics

Christian,

Im not a subject expert, but I am not aware of any brand of 1.2meter antenna that has the feed arm connected to the frame. (There may be one out there but Ive never seen one)  I prefer Skyware type 183 design but thats a 1.8meter. The feed arm is securely bolted to the frame (not the reflector) while it does have the support arms from the mounting block to the dish they are designed for ensuring the focal point and reinforcing the dish against wind instead of supporting the feed. I also think the 183 has the best (strongest) mast and EL/AZ adjustment design on the market. All just my opinion but Ive dealt with hundreds of 1.8 and 2.4's an have never had a problem with Skyware (formerly Raven) but Ive seen a few Prodelin's with sheared bolts, and other issues.
As for the Class question - Class III are heavyweight, "industrial use"designs and Class I seem to be "Home user" quality.

Unless someone absolutely needs a small form factor design of a 1.2m (like for building code restrictions) Id always advise to go to a 1.8m Type 183.

Thanks for info, Dave: quite useful! Sorry for late reply, but I am on HI time zone.

Did you mean you don't know of any 1.2 dish that does not have CONTINUOUS >metal< from the post pipe to the metal of the feed structure?  Lucky you!

Is there a STANDARD SPOT where I should search for "fine print" ID on dish reflectors? I haven't found much of anything so far.

My RavenSkyware 122 uses the VERY SAME SIZE ribs on the back, that hold a few ounces of skin at the top of the dish, as for holding the 3 foot cantilevered lower leg that is loaded with tons of cast aluminum BUC...   And also to take the pull of the side legs...

Just measured: 22' of plastic to go from the nearest mount bolt to the metal bottom leg foot. And 20 inches of plastic betweeen the mount metal and the feet of the metal side legs.  The metal mount is just tied to a center patch of the plastic reflector with 4 bolts on only a 7" square pattern. The ton of cast alum on this 4 footer dish is cantilevered over 3 horizontal feet away from the center of that 7" square!

The "Raven-like" dish with the 1/2" SE (String Error    ) is quite similar in insane engineering. 1.5 years from brand new un-packing.

The Andrew 3 040 942 with the 5/8 SE, is 5 years old, has the mount bolt pattern extending DOWN toward the bottom leg by a few more inches (like on pics of Eric's links, where possibly the ribs look taller as well as perhaps containing a higher concentration of glass fibers...), so a bit less stress on the plastic in this case, on that one leg, BUT, once again, the rib size is the same as at the top of the dish.

Eric: if your links show a much older Andrew, would you know if the bottom ribs going near the foot of the bottom leg, could be oversized? (I once had a DirectWay very elliptic dish done that way). Your pics show square-patterned ribs, and the dishes here are all "triangulated" pattern. So may be you have an earlier US-made original version?

I managed to have a peek through the fence, at a recently installed ChannelMaster 6 footer, and sure enough it is all the same, just scaled up, with just 4 bolts tru the plastic, that are quite a bit more spaced of course, but still same tiny ribs all around the dish and zero metal beam that I can see from a distance, from the metal cap mount to any of the 3 metal legs -just feet of plastic.

There is about 13 of these systems on the atoll, all from the same service provider, most 4 footers, most under 2 years old, and only 3 are 6ft.

Dave: where can I find www drawings of the back of your well engineered dishes? And get some ideas about designing a 3 pointed metal beam...   I spent a few hours yesterday but could not find any.


Eric: for various reasons my own Raven-122 is temporarily installed on a palette, in the "upside down" attitude, for minimum footprint, ie spun 180 deg aroung the "lower leg"; we end up with the reflector somewhat flat (around 11 deg from hz, for my 54 sat elev, and I had to drill a rain water drain hole), and the tripod is on the high side of the satellite beam, not below. I also have the whole thing resting, just with gravity help, on just 3 home made adjustable jack screws, located at the reflector PERIMETER.

a-this Raven is also 2 years old and the string test is rather perfect!

b-in a general manner, the 3-legged pyramidal feed support is now well upright, with the ton of cast alum rather pushing downward and evenly on the 3 legs. In my case the 3 jackscrews are near the 3 leg loads, for absolute minimal stresses.

c-the center of the skin, a the 4 mount bolt holes is fully unsupported, so perhaps in a few years the plastic of the dish center will sag down from the well supported rim, and the dish will take a deeper shape -wet noodle style!

d-as the huge cantilever (torque at the mount 4 bolts) is much eliminated, for people using the standard "pole and cap mount", why not remove the 4 center bolts, spin the whole dish 180deg, rebolt, and figure out what correction to apply to the factory elevation scale. If this was done at original install time, it might avoid all distortions whatsoever for a lifetime?

e- in general what are the cons with the upside down attitude? Horn looking more downward and getting a bit more noise from the ground? Or catching LESS noise if installed over a tin roof? Condensation more likely to drain to the horn window, and away from the electronics. In my case I'm unable to see a difference, over concrete floor...

f-another option to completely avoid distortion: built a gantry straight above the CG of the feed assy, rig a couple of pulleys, use a small rope and a carefully adjusted COUNTERWEIGHT!

g- I just can't believe how insane the whole mickey mouse thing is!


RE: if a dish is distorted, pull it straight if possible...

The problem is when we get to an extreme 5/8 in "SE", we really need to know what proportion needs to be "pushed back" into the sides, and how much pulled up from the bottom.

If not, applying the wrong proportions, in first approximation the dish becomes either shallower, or deeper, and the feed horn needs to be moved back or fwd, to the new focal length....

There is also the issue of plastic creep: if constant correcting forces are applied will the plastic keep moving mm's for weeks and months?


In my case I'm thinking of making a glued 4-arms reference jig (same geometry as the 2-strings) from my apparently perfect Raven; and as we are hunting for almost an inch, it will likely be appropriate for most brands of offset 4 footers that are wildly out of shape...


Thanks guys

Christian

Sorry I misspoke (or mistyped!) I meant to say that Ive never seen a 1.2 that HAD the feed arm directly bolted to a metal frame!

Every 1.2 Ive ever dealt with had the feed arm mounted with a single bolt thru the fiberglass at the base of the parabolic.

I will look around and see if I can find a engineers drawing of those type 183 antennas.

Ive also pondered the idea of making a additional support arm using all thread rod to support the feed arm - especially when using larger BUC's.