Do mesh or transparent sat dishes give less signal?

[Peter Scott]

I've now set up two satellite systems. The first has an 80cm 'transparent' plastic dish with a mesh core. The second is a 60 cm solid metal dish. I believe both to be aligned correctly. Both systems work fine, but I get a better signal from the smaller metal dish (about 3dB). Both have a clear-sky view. I suppose it's possible that the lnb in the larger dish is at the bottom end of the quality range for the product. However before I start mucking about with it (not the right weather), does anyone know if, in general, mesh dishes give a poorer signal, particularly when the mesh is embedded in plastic?

Peter Scott

[1501]

As long as the "holes" in the mesh are small compared with the wavelength of the microwave signal the dish will still act as an excellent reflector.

[meow2222]

the hole size is a small fraction of the wavelength, so it makes no difference. Look at differing LNB specs, or maybe alignment / cable / minor damage.

NT

[Dave Liquorice]

Our system (Zone 1 painted mesh minidish) stops working once the ice build up gets above about 1/4" thick. We normally have a full or one block missing signal strength of a Sky box and quality perhaps 2 or 3 blocks missing. I wouldn't expect a thin bit of plastic to make a significant difference unless there has been a very bad choice of plastic made.

Do the LNBs have the correct feed horn for the dish shape (circular/oval) and their position (offset/not offset) relative to it?

[robert]

Are you using the same digibox to compare signal levels , and I would expect LNB's to vary quite a lot , otherwise why are some makes 5x more expensive than others ?

Final adjustment should be for signal quality not strength .

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Peter Scott saying something like:

Yes, but not so you'd notice much. It was more of a concern ~15 years ago, before decent LNBs came on the market. The plastic isn't a factor, imo.

[Peter Scott]

Thanks for all the comments. I use a Satlook Micro for alignment. Looks like it's an iffy lnb then. I believe that they have a fair spread in performance even in the same model. I'll fit the Titanium quatro ready for the multiswitch and see if I get better numbers. It's a relief about the plaggy dish. I am in a conservation area so it's politic to keep it as unobtrusive as possible.

Peter Scott

[Andy Wade]

Peter Scott wrote: ,

You started by mentioning a difference in signal of 3 dB, without saying whether that was in level (amplitude) or in S/N ratio. LNBs are high gain devices; their overall gains are typically between 55 and 60 dB, with a wide tolerance. Two perfectly good LNBs of the same make and model could easily differ in gain by 3 dB and such difference is of no practical consequence.

A 3 dB output level difference between two dish/LNB set-ups is only significant if it's due to front-end factors - i.e. a genuine difference in dish gain, mismatched dish and LNB feedhorn F/Ds, or just poor LNB positional set-up.

So compare the RF S/N ratios (aka C/N) or, failing appropriate instrumentation, satellite receiver signal quality (BER) displays before condemning your dish or LNB. Ignore signal strength (unless grossly low).

[Peter Scott]

Thanks for the suggestions

I'll climb the scaffolding when it stops raining

Peter Scott