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rain, fringe & prime focus

hedge

Regular Member
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My Satellite Setup
Soon heading for the nearest skip.
My Location
SW Algarve. Portugal
#1
The face of the LNB on a prime focus dish points up far more than with an offset dish....so, when it rains any cover over the LNB will be less effective.................& it does rain in the SW Algarve.

Is this reason alone to avoid a prime focus dish?

Reason i ask is because a near neighbour (about 6km away) has one, but only because 'the installer recommended it'...........whereas nearly all others wanting UK TV have a 1.3 - 1.4 offset dish....whether using FTA or Sky receivers.

Thxs

Hedge...probably going in circles again!
 

bignick

Specialist Contributor
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My Satellite Setup
Back in the UK and missing Cyprus!!!
My Location
Aylesbury
#2
hedge said:
The face of the LNB on a prime focus dish points up far more than with an offset dish....so, when it rains any cover over the LNB will be less effective.................& it does rain in the SW Algarve.

Is this reason alone to avoid a prime focus dish?

Reason i ask is because a near neighbour (about 6km away) has one, but only because 'the installer recommended it'...........whereas nearly all others wanting UK TV have a 1.3 - 1.4 offset dish....whether using FTA or Sky receivers.

Thxs

Hedge...probably going in circles again!

Prime focus dishes have certain advantages over offsets but these do not start to become relivent until you go to dishes in excess of 2m. I think for a 1.4 or 1.5 then I would stick to an offset with a good quality LNB on it.

Also, regards your other post about dish types. Ali dishes will be ok normally! I wouldn't have any quarms about buying one. The high quality ones such as Andrews etc are better & do last longer, and of course do cost more money - however they are perhaps over engineered for your purposes as they are also designed for Vsat use which you do not require.

Hope that helps

Nick
 

geoffrey

Regular Member
Messages
131
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20
Location
Zichron Yaacov
My Satellite Setup
2.4M ChannelMaster Offset with Smart Titanium TQS LNB. LG SMART TV with SuperTrack V-Box 2 on ChannelMaster 1.2M Offset. TBS5925 tuner with EBSPro on Windows 10 laptop. Satlook Digital NIT.
My Location
Israel
#3
What's the problem with big offset dishes. On paper the Prodelin 3.8 offset performs as well as a Prodelin 4.2 Prime focus - or is there a catch ?
 

hedge

Regular Member
Messages
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My Satellite Setup
Soon heading for the nearest skip.
My Location
SW Algarve. Portugal
#4
:-doh!Gentlemen, you are so polite, & have not as yet told me what a total plonker I am!

Biggest senior moment so far this lifetime, I even changed my post after I had it right first time:-idiot...............

Start again:-Prime focus dish points up(ish), so LNB points down(ish)!!!! -- It's the performance advantage in the rain I was thinking of.....If I can cover the rim of the LNB so the water cannot run across the face then it has to have a better wet weather performance than an offset dish which I cannot successfully protect from certain near horizontal rain directions.


That's better.....now I am impressing myself .... for the moment:rolleyes:
 

Likvid

ASBO Club Member - Persona non grata
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My Location
Stockholm, Sweden
#5
Nothing beats a spun aluminium dish in performance, plastic dishes like Andrew has a thin coat of gelcoat i beleive that the signal has to pass thru until it reach the zink/alu coat underneath.

Plastic dishes do get old and it's a myth they last forever, i have seen Channel Master 1.8m dishes and some Swedish made plastic dishes that cracked from the inside of the thin plastic coating.

What happens after that?

Well, with environmental effects wet and rainy weather eats thru the plastic crack from the inside and you get bubbles in the plastic which looks like huge bumps.

I am not kidding.

Problem with metal dishes?

There are some problems with metal dishes, badly designed dishes can warp after some time and exposure to strong climate changes in temperature.

Shipping metal dishes safely is another problem, but nothing to worry about if you buy from Precision or DH antennas as they will ship them in a wooden crate.

Cheap dishes like Gibertini and such are sent in a cardboard box, if someone jumps on it during transit the dish will be damaged.

No there is no secret the Prodelin 3.8m is better than the Prodelin 4.2m prime focus.

But in the end for dishes larger than 1.8m prime focus is the king when it comes to flexibility, there is a large market of feeds to choose from and prime focus dishes looks nicer and easier to work with as you don't need to know the offset angle and such.
 

Orthoclipse

Regular Member
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127
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My Satellite Setup
Various
#6
There are two main reasons given why small offset dishes outperform small prime focus dishes.

A prime feedhorn shadows more of the dish than an offset feed. As the dish size increases, this effect becomes less important.

Unlike prime feeds, offset feedhorns point away from the ground and are less prone to picking up ground noise.

re: your original question - water on the feed has a negligible impact in comparison to rain or moisture in the atmosphere.
 

hedge

Regular Member
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My Satellite Setup
Soon heading for the nearest skip.
My Location
SW Algarve. Portugal
#7
Thxs guys.

I have also seen a large plastic dish with cracks.

I was wondering about the shadow problem, now I know:)

As regards rain, I can honestly say my experience is the opposite with fringe reception; or rather, if I wipe the LNB I get the signal back. Though it was joy after radio 3 went to a wide beam & I was listening to a symphony whilst watching my crap 1.0m dish wobbling in the gale & rain coming down in sheets.

Hang on Likvid, Gilbertini...'cheap'?! -- now didn't I see this make praised elsewhere?:)
One moment please....age 57 ....average male lifespan.. 70 something........computing.....Nope, not enough to learn what I need to learn on this subject...total shut down; just like my sat receiver does 3/4 times a week
 

hedge

Regular Member
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My Satellite Setup
Soon heading for the nearest skip.
My Location
SW Algarve. Portugal
#9
Thxs Orthoclipse:)

I was already going off the prime focus after reading the 12 page 2D in Sicily thread! .....................Pity, as a giant prime focus would be more of a talking point; large offsets are just so common around here ;)
 

hedge

Regular Member
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My Satellite Setup
Soon heading for the nearest skip.
My Location
SW Algarve. Portugal
#10
That's torn it!
Spent half of yesterday with a friend's 1.3m offset & my receiver.

Checked the alignment, fiddled with the skew, we could not improve things. Could get film4, & ITV 2&4...but he said they are marginal in the evenings........which rather defeats my object as these were the channels I wanted to get reliably.

OK, it could be his 'silver Inverto miracle 0.2 (weighted against thin air) dB' lnb.....I have one myself & my two LIDL lnbs outperform it...............but overall, despite what the dealers say here (a couple say 1.4m is required) I am thinking I need a much larger dish.

Then, I see that the tin-ware maplins Fortec Star (I.8 & 2.4) can be delivered to Portugal for about £15!!! (no joke)..........So i'm tempted to take the risk........but what do I use for a feedhorn please (having just got my head around what one is!)

Decisions decisions

& to think, i was once at the 'leading edge'..............35 yrs ago..........seems like only yesterday..............& who changed the name from PCM to Digital?? - I missed that one:-doh2

Sorry for going on, but I'm slowly getting hooked.......
+ I hate throwing good money at something blind...............OK OK, I'm a cheap skate
 

dxsat

Specialist Contributor
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745
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70
My Satellite Setup
Snap's setup: (In Spain) Humax HDR, Prodelin 1.8m dish + Invacom QDF-031 + CM feed, (In UK) CallFlow VDSL + EE 4G, Sky Q, YouView HD, Mac OSX, iOS
My Location
UK: Tonbridge, Kent. Spain: Madrid.
#11
Don't bother with the Fortec Star, they are a major waste of time & money.
Never seen a cracked Andrew dish, have seen them after up to 10-15 years old in hot Spainsh sun, they are the best offset by far, ask any reputable installer. Prodelin are very good too, build quality slightly lower, but performance the same.
Rain on front of the LNB is a significant problem for Astra 2D reception in weak areas. Best cured by fitting a rain shade made from plastic, like that fitted to a telescope. I make mine from Carrefour croissant boxes.
 

hedge

Regular Member
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My Satellite Setup
Soon heading for the nearest skip.
My Location
SW Algarve. Portugal
#12
Hi Snap, thanks for your trouble.
The continuing saga:-I do use a rain shade,(plastic tonic bottle), works well with a southerly wind, but not with a northerly as the shade needs to project further to keep the rain off & it starts to block the signal.......not sure in theory if it should, but it does:confused

It was because of the rain problem that I thought the prime focus might be better (LNB pointing down)........... a 2.4M for £200..........& yep, I have a problem avoiding Victimville..... I thought I may be able to reinforce the beast.......

I have a more sheltered area that is next to a shed 2.6M deep & has a good site of 28 deg. east straight down the land; I could even build a concrete structure to support the infamous Fortec Star petals....I thought, as once it's on 28e only the next earthquake will shift it..........fine adjustment could be fun, but I like a challenge:-ohmy
It is 50 metres to the house though, will this be ok with a weak (ish) signal though?


I don't see the point of going just above marginal. I have been reading the ex-pat forum for here, & on various threads all of them have problems with some signals in the evenings after a 'professional' installation! ......hence the bigness factor. (The sad part is not one of the posts (& there are many) mentions a world beyond Sky! -)

Am still looking at the two makes mentioned...........2.4M offset £2675 !!!!! Ok it includes feedhorn & lnb, but not the staggering additional delivery charge...........Please tell me I'm looking in the wrong place guys?? !!!

A 1.8M offset then? in the Algarve? at a sensible price? - still working on that one also

As a neighbour said: It's lot of dosh for a very large wok:)
.........................................................................................................
Thxs for a great site.........I spend about 2 hrs a day reading.........& trying to gently get my head around this near infinite subject............
 

dxsat

Specialist Contributor
Messages
745
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70
My Satellite Setup
Snap's setup: (In Spain) Humax HDR, Prodelin 1.8m dish + Invacom QDF-031 + CM feed, (In UK) CallFlow VDSL + EE 4G, Sky Q, YouView HD, Mac OSX, iOS
My Location
UK: Tonbridge, Kent. Spain: Madrid.
#13
Hedge,
Just realised that you may be going for overkill. There is a member of Astra 2D forum, webname Rato, who lives in Setubal south of Lisbon. He reports getting good BBC reception on a 1.2m dish. You may well find this size will also work in the Algarve. You may find it useful to contact Antent Digital in Madrid, where I buy my dishes. They have one English staff menber and I think they have an associate in Portugal. They would be able to supply a dish, Lnb (Invacom's Spanish distributor)and the mount you will need.
http://www.antnetdigital.com/ Their phone number is on the website.
A 50 m run to house is no problem provided you use PF100 or equivalent cable (copper outer sheath)
 

hedge

Regular Member
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My Satellite Setup
Soon heading for the nearest skip.
My Location
SW Algarve. Portugal
#14
Thxs Snap.

Being a bit perverse (+ the fact I might be able to do it for a similar price!), I don't mind overkill in this case..:-nuts..?? ---- Tried a friends 1.3M earlier in the week....the 'report' is in one of my earlier rambling posts on this masochistic thread......it wasn't good enough.........the dish I mean..........erm, & the post. --- So the cheapo biggy we could label 'future proofing'?

I meant to PM Rato as in a thread way back he said a biggish dish could be had for about 50€ !!! .... so thxs, you have inadvertantly reminded me:) ....I'll do it now.

I believe the Lisbon area makes less demand on dish size

& thxs as ever for the other info, & link
......................................................................................................
To be continued...........sorry.............Wake up at the back please, this is pioneering stuff; for meO-no