Holes in Mesh

[jagee]

I is it true if the holes in a mesh dish is more then a pencil thick it will not pick up KUBand?

 

[chefwan]

I is it true if the holes in a mesh dish is more then a pencil thick it will not pick up KUBand?

i think the guys in here have said they have to be small enough for a pencil not to go through

 

[gabshere]

i think every dish is a bit different , but as a golden rule for Mesh and this is the woven mesh its a pencel lead or 1/16 of an inch .... now some dishes differ like the birdviews which use a solid metal and perforated hole in it, can pass the whole pencil through and still get great ku reception.

this is just a template and you would have to check the dish to find out for sure
mesh dishes are more common. some have a lighter mesh which deteriorate faster and some have a stronger mesh the stronger mesh dishes probably would have better reception than the lighter mesh (almost like a window screen)

so if i rated them it would be (and i would say the birdview might be the exception to the solid / mesh discussion)

1)solid metal dish
2)heavy mesh
3)solid fiberglass (some of these used a light mesh and have poorer ku reception) also fiberglass dishes tend to be very heavy which is a downfall for moving them

4)light mesh ( i would feel have poorer ku reception and high deterioration rate)

 

[jagee]

Good information to know.Thank you

 

[linuxman]

Just to add to what George has said.

The Birdview perforated will not pass the #2 pencil through. Almost, but not quite. The #2 pencil is the test for well-formed perforated reflectors.

The problem starts occurring because stretched mesh dishes often don't have the well-formed parabola needed to reflect the signal into the feed-horn. A lot depends on how the petals are put together, and how well the mesh fits on the supports etc.

That is why perforated metal is generally better than normal mesh because it holds the form better.

But what George has outlined is a good rule of thumb.

Fred

 

[caddata]

I is it true if the holes in a mesh dish is more then a pencil thick it will not pick up KUBand?

jagee:

Any mesh or perforated dish that will reflect C Band microwaves efficiently will also reflect Ku Band microwaves. However, the higher the frequency, the smaller the openings for proportional efficiency. A dish with 1/2" openings may be 75% efficient for C Band yet be only 15% efficient for Ku. The Ku Band dish would have to be much larger than the C Band to produce the same signal gain.

The No.2 pencil test has been the rule of thumb since Ku began to be used for satellite communications. If the pencil won't pass thru, the Ku microwave thinks the dish is a solid reflector for all practical purposes.

Perforated (sheetmetal with holes punched in it) dishes hold their parabolic shape just as solid sheetmetal one's do.

The problems that mesh (woven wire or hardware cloth) don't hold their shape well and the surface is not flat combine to reduce the efficiency to much less than a similar perforated.

Most expanded and flattened sheetmetal dishes are unacceptable for Ku because the long opening dimension (openings are oblong) is usually much greater than the small opening dimension. The pencil won't pass thru the small dimension but it flunks the test because of the long dimension.

Hope my reply wasn't so long that it became boring.

Harold

 

[linuxman]

Hey Harold,

I was hoping you would chime in with your usual completely thorough and easy to understand explanation.

Fred

 

[jagee]

Can you take very flexible sheet metal and cover over the dish to make it works or not.Or an aluminum of some sort or something so as not to waste the different dish.Or can you fill in the holes with anything.Just something to think about.

 

[caddata]

Can you take very flexible sheet metal and cover over the dish to make it work.....

Think about a few things:

(1). Are the struts formed to an accurate parabolic curve. Inaccurately formed curve distracts greatly from the gain of the dish. A 12 foot poorly formed dish may only perform as good as a 3 foot accurately formed dish.

(2). If you're using screen wire mesh, what helps form the parabolic curve between struts? Remember that wire mesh can't be preformed, but must be stretched or allowed to sag into the proper curve. Curve might be accurate during installation but what happens afterward, when temperature and wind extreems change the curve? There's that 12 foot dish that really is a 3 foot.

(3). It would be nearly impossible for a novice to form sheetmetal panels to fit between struts and maintain an accurate parabolic curve. The curve has to formed in 3 dimensions into a parabolic shape. Again, you'd need a 12 foot dish to give the performance of a 3 foot.

None of the alternative fixes seem to be practical. Time and effort would be better directed to locating an old (used) dish, of adequate and quality construction.

Harold

 

[jagee]

To all persons giving me some feed back i thank you for all your answers,They were all interesting.I just thoght this would be of some use not only for me but to others as well.Thanks once again.

 

[Steveo]

Here is my theory on the subject that I mentioned if another thread.
http://www.satelliteguys.us/showthread.php?p=891037#post891037

A solid dish will not have any big improvement on Cband. However if you do want to receive Ku off the same dish. A solid dish would be better. Not so much in the fact that it has no holes like mesh but because the surface accuracy of solid dish is usually so much better. It is a common misconception that so long as the holes are small enough (actually less than a 1/4 wave at the frequency) it will be ok for Ku. For Ku the wavelength is so much shorter, so therefore there is more refraction. As a rough analogy think of it as a sound wave. The longer bass wave kind of gets thru, like a sub woofer, it not critcal where you place it. There is less refraction but the tweeter, to hear the higher sounds best it must be an uninpeded path to your ear.
The good news is apart from the shear size of everything Cband is a lot more forgiving. Than the tighter tollerances of Ku.

As caddata mentioned a perforated metal dish may perform better than a mesh dispite the fact it may have larger holes than the mesh. Now there would be loss thru the holes but the better parabolic shape will more than make up for this.

 

[Likvid]

There are no losses if the holes are smaller than 0.254

That is why the Winegard Pinnacle dishes were the best mesh dishes out there in the beginning.

 

[jagee]

Man this is a great site you guys are the bomb,I hope i can be of use one of theses days to help someone out with the right answers,and if not ill just sit back and raaed all the good stuff you guys and maybe women put pout,Thanks again,I just found a 12 yr ols BUD 4 miles dn the road from me,to have if i take down.Great! huh.I caught the bug again.