Anyone know about ISS dishes

pedro2000uk

Anyone know about ISS dishes-?

rolfw

Yes, relatively low cost, relatively low quality. I wouldn't use one out of choice.

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pedro2000uk

Thanks Rolfw,

I noticed the ones we've seen recently are very light (because they are so thin now) especially the mesh versions- but the shape of the dish looks as though it should perform OK with a good lnb (and a bit of light weight strengthening to stop wind bend)-
The lower weight and lower wind loading of the mesh versions favour the limitations of diseqc motors.... if we can get enough out of them to do the job they're for they'll do.


Anyone played with the mesh or solid 1m versions lately?

rolfw

Definitely don't touch the big ones, the brackets on the ones I have seen have been flimsy as well, not good for motor mounting as they add another area of dish movement to the equation.

Get yourself an Aluminium Fracarro Penta dish, nice and light, reduced windage, solidly built and will perform as well as a cheap 1m dish.

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pedro2000uk

Thanks again Rolfw,

you're bang on about the bracket on the back of the ISS's- we'd stiffen that up too laterally - it's OK vertically, although I just checked a very similar dish bracket and I thought I had done that but never got round to stenghening it since I noticed it too.... about x years ago.... too busy/forgot, but I bet it lost the signal in striong winds a few times on a weak sat just on that mechano-y bracket, but it's a lot easier to adjust than say the the Triax beast that is solid as hell but a cow to fine adjust and especailly to add an incline screw adjuster or motor to.

Nice advice about the Aluminium Fracarro Penta dish - will have a good look at it - where is that 85cm measured and what does the scalar cone view see? inside the whole dish or including the points and gaps outside the dish at the narrow bits?- does that shape dramatically reduce wind loading or something, do thay make a feed horn or an lnbf with a feed horn to match that shape. I really don't know anything about that design and it throws up a lot of questions when you are just used to tweaking round-ish dishes and round lnbs etc..

rolfw

The 85cm is on the square, the width from corner to corner is from memory 98 cm, the height from top to bottom, see post below.

http://www.satellites.co.uk/satellit...30-post27.html

View this thread for more info.

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pedro2000uk

Many thanks for that info and thread... the overall area is about the same as an 85cm round dish- 77+((91+98/2)/2) less the corner bits = 85-ish. Then the lnb sees right to the points and the gaps so their is a gain but also increased noise. The square shape may have known advantages but far more likely is the dish curve is well engineered.

I think the steel Triax are a bit lumpy and not as uniform as I'd expect and the ISS looked far truer if flimsy- the triax steel dishes won't flex in wind - the iss will- the penta won't and I asume are a truer curve than the triax so overall it's probably a good comprimise and the ali ones aren't that much dearer and probably save on trashed diseqc motors.

still like to see a comparison with a 1m dish on a weak sat and noise levels- they quote 39db gain at lower freqs in ku band about the same as a 1m but no higher ku freq figure to reflect near 40.5db.

rolfw

I certainly didn't notice a higher noise figure, in fact the signal to noise ratio was excellent throughout the frequency range.

I've been unable to do a direct side by side comparison with something like the ISS, as I would have to first buy one but then would not want to sell it to a customer afterwards and I'd end up being stuck with it.

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pedro2000uk

I agree, we experimented with butchered Sky Grundig lnbs taking them out of the plastic case and putting 40mm sleeves on them on normal dishes and were amazed at the performance compared to a lot of good reputation lnbs too (just done the same thing on an 88 mesh dish and they beat all but the invacom). The lnbs have an offset eliptical scalar ring design so some of the signal area was outside the dish and they still did far too well - scalar overbite didn't make a lot of difference- but it must make some surely depending on what's behind the dish.

pedro2000uk

Had time to check those Aluminium Fracarro Penta dishes a bit more and they are a good recommendation for a good solid reliable dish to go on a diseqc motor - those installations look really good too, you can see they are a good choice for a reliable installation- we(I) like messing, engineering wise, and any dish that I go near usually gets modified, not really too viable for regular professional installations.

You still need the side by side acid test on a well known fringe satellite like 26e between the Penta and a basic 1m dish and haven't found an example of that unless we do one. My instinct is that even the ISS 1m mesh will beat it on a calm day after maxing both out with the best LNBf matches etc... but the ISS’s still need bracing.

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It's a recurring problem with diseqc motors- if you want to put the larger dish sizes on them you have to get the weight down- ali or thin steel/ mesh above 80cm if it's a 1.2 max motor or see the motor fail early and it doesn't help that the motors are usually only advertised with the max dish size and dishes often without their weight.