Solid versus mesh dish for ku

[gordonkearse]

Was just viewing the previous thread and didn't really want to hijack it. So has anyone experimented with solid versus mesh dishes for ku?

Right now I'm noticing my ku quality is significantly lower than c-band quality on my 10 foot perfect ten mesh dish. I've adjusted and adjusted the lnb.

I've considered putting up a smaller 6 foot solid dish to compare the two for ku signal strength and quality.

 

[caddata]

Use a No.2 wood pencil as a go-no go guage to test the reflecting surface. The rule-of-thumb for a Ku capable mesh/expanded metal/perforated dish is: If a No.2 pencil (wood part) will pass thru any opening, it's not suitable. Any surface material that the pencil WILL NOT pass thru, is seen as a SOLID SURFACE to the Ku frequency electromagnetic signal. If your dish reflecting surface passes the pencil test, there's some other reason for low signal strength. Reasons can include, dish surface not a true parabolic, LNBF not at exact focal point, dish not looking directly at signal source (satellite), LNBF not adequate in gain, feedhorn not optimized, trees or obstructons in field of view, or numerous other reasons.

 

[SatelliteAV]

To add to Caddata's excellent information.... In my experience I have found that a mesh dish for KU-Band will never perform as well as a similar sized solid or perforated reflector. A fiberglass dish will have varying performance depending on the type of RF reflective materials used in the forming of the dish and the support of the parabola. Some fiberglass dish designs do not age well and the parabola tends to warp.

Loved my 12ft Paraclipse for C-Band, but it performed similar to a 4' offset for KU and was difficult to keep on KU satellite signals during any wind.

 

[B.J.]

Unless the mesh dish is very very old, I'm confident that the mesh is small enough that it is 99% as efficient as a solid surface. But as the above responses mention, shape of the dish is really a critical factor, and it's very common that a mesh dish doesn't have very good shape. {Actually, the shape should in theory be an elliptical shape, not parabolic, but this is a trick statement, because at these distances, they're essentially the same.}
Also, as mentioned above, having the focal distance set properly, is very important, because with Ku, if the focal distance is set wrong, the signal pattern will look more like a donut than a spot.
But the main reason for responding is that even though most C/Ku feeds don't illuminate well for Ku, and the dish shape may not be perfect, and the focal distance might be off a bit, since the Ku sats are generally more powerful than the C-band sats, and since a dish theoretically will have a higher gain on Ku than C-band, and since a big dish will generally have more resolution to reject adjacent satellite interferrence, you'd really expect Ku performance to be better than C-band, unless the dish is really in bad shape.
In MY case, when my 10' mesh dish was new, it performed pretty well on Ku. Significantly better than a 3' solid dish, and much better than a 6' mesh dish I have. However over the years, it has gotten dented and warped, and it now gives extremely poor performance on Ku. I've tried all sorts of things to get my dish back in shape, but so far nothing's worked. I think that when the weather gets better, I'm going to pull out some of the mesh panels and see if I can flatten them, but I'm not real optimistic that this will help. I really think that I need a new dish.

 

[caddata]

......Actually, the shape should in theory be an elliptical shape, not parabolic......

Not true. The reflecting surface is parabolic in shape. All parallel waves (electromagnetic, light, or sound) striking it's surface are reflected to one point, travel the same distance, and arrive in phase with eachother at one focal point.

An elliptical surface has two focal points, reflected waves travel unequal distances to those focal points, and arrive out of phase with eachother. Elliptical reflectors are used for lights and parabolic reflectors are used for satellite dishes.

Any reference to elliptical when discussing satellite dishes is in reference to the shape of the outer permiter of an offset focal point dish. Prime focus dishes have a round perimiter.

 

[B.J.]

Not true. The reflecting surface is parabolic in shape. All parallel waves (electromagnetic, light, or sound) striking it's surface are reflected to one point, travel the same distance, and arrive in phase with eachother at one focal point.

An elliptical surface has two focal points, reflected waves travel unequal distances to those focal points, and arrive out of phase with eachother. Elliptical reflectors are used for lights and parabolic reflectors are used for satellite dishes.

Any reference to elliptical when discussing satellite dishes is in reference to the shape of the outer permiter of an offset focal point dish. Prime focus dishes have a round perimiter.

Well, I kind of agree, and kind of disagree.

But the reason why I contend that it should be an elliptical surface is because a parabolic surface will focus parallel rays to a common focal point. An elliptical surface will focus rays which come from 1 specific point, which just happens to be the other focal point of the ellipse. Ie an ellipse has 2 focal points, which are often used to draw them via a string tied between them. For an elliptical surface, RF coming from one focus will be reflected to the other focus. A parabolic dish only focuses to a single point if the object is infinitely far away, and the sats are at a finite distance.


I think I see what you're saying though about the phase issue, although the drawing via a string analogy would seem to suggest that it WOULD be in phase, but even if it is out of phase, I guess that means that neither a parabola nor an ellipse will work perfectly. A parabola won't focus to a point, and an ellipse may be slightly out of phase. But the real bottom line is that an ellipse that big is essentially the same as a parabola, so there isn't much difference.

I hope I don't confuse things by having edited this about 6 times. I've gone back and forth between disagreeing and agreeing multiple times, which means this is a really interesting topic.

 

[Anole]

back on topic:

Was just viewing the previous thread and didn't really want to hijack it. So has anyone experimented with solid versus mesh dishes for ku?

Right now I'm noticing my ku quality is significantly lower than c-band quality on my 10 foot perfect ten mesh dish. I've adjusted and adjusted the lnb.

I've considered putting up a smaller 6 foot solid dish to compare the two for ku signal strength and quality.

I believe there are a number of considerations to getting a good Ku signal.

- most Ku signals are sufficiently powerful, to be received in their target area on a modest sized dish.
- some Ku signals have neighboring satellites spewing interfering signals on a nearby frequency.
- unfortunately, downlink signals can be attenuated by weather
- uplink power on most FTA doesn't seem to be monitored to provide constant downlink signal

- dish surface accuracy at Ku is of paramount importance
- transmit-certified Ku dishes may be able to provide a cleaner signal by virtue of sharper focus

So, if your 10 foot dish uses a large vs small mesh, sags or has other imperfections, is equipped with a non-optimal feedhorn, or is aimed at easy vs difficult Ku birds, it may or may not get the job done.
On the other hand, a surplus 6' Prodelin, taken from 2-way service, and outfitted with the proper feedhorn, -might- blow the doors off a 10 or 12 foot BUD... for Ku.

The point being, there are a lot of factors to take into consideration.
Focusing on just one or two, can lead to inconclusive results.
Of course, going ballistic, and spending $5000 on your Ku dish, is just as bad.

Maybe look into how users report their 1.2m dishes perform on the satellites you watch.
That might be a good solution... to size, weight, matching feeds, motorization, etc.

 

[caddata]

B.J.:

I don''t want to hijack this post by concentrating on the shape of a reflective surface, but I can't let the things you're saying go by without comment.

How'd you get so confused on this subject? There's never been, and never will be, a "dish" antenna manufactured with an elliptical reflecting surface. Show me the specifications of a "dish" antenna that states the reflective surface is elliptical in shape.

Any reference to "elliptical" is related to the shape of the rim (offset feed as opposed to prime focus which is usually round). The elliptical shaped rim can be used to limit adjacent interfering signals even on prime focus antennas.

......A parabolic dish only focuses to a single point if the object is infinitely far away, and the sats are at a finite distance......

A parabolic "dish" focuses all parallel signals (electromagnetic, light, or sound) to the same focal point, whether the source of the signal is 6" or an infinite distance away.

 

[gordonkearse]

I've got to admit that most of you have thought long and hard over which dishes work the best and why -- at least in theory.

And so often I see photographs which show the same people with multiple types of c and ku band dishes. I guess they are experimenting, too!

I've thought long and hard about whether it was even worth it to set up old 10 foot fiberglass dishes. Many appear very heavy duty. But I sometimes wonder how much time has degraded them. Indeed, they could be affected by material breakdown or become just a little warped.

Your discussions keep bringing me back to the issue of focal point. I have still never checked my BUD for this. I'm sure I'll get to it at some point.

I do notice a few small dings due to sleet over the years. My ten footer is a 1993 model so I don't really expect it to be perfect anymore.

Thanks for the input.

 

[truckracer]

I have a 7.5' and 10' mesh dishes both with c and ku. I have a solid fiberglass commercial prodelin 1.2M receive/transmit dish. Both my big mesh dishes seem to perform equally as well and better on some ku sats than the dedicated ku dish. i know this sort of goes against the grain but its has been my experience.

i am using corotor II feedhorns with norsat lnbs for both c and ku.
my ku lnbs are PLL type.

i was using the ku lnb that is mounted on the transmit radio on the prodelin.

If your mesh big dish is straight and not warped or sagging, properly aimed with a nice line of sight..it willl peg the signal meter in most cases on ku.