LNB skew adjustment on old Grundig Sky dish

Discussion in 'Sky Digital TV Forum' started by wwmac, Feb 18, 2013.

  1. wwmac

    wwmac
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    I would be grateful for any assistance.

    I have got an old Sky dish (Grundig made, pics attached) and I intend to adjust its LNB skew to get a better signal quality from HotBird (-10.6º vs. -13.6º required for Astra), however there does not seem to be any screw or bold which I could loosen to rotate the LNB. Is there any way I could change its angle?

    Alternatively, I could replace the LNB with the modern one, however I am also reading that due to a smaller arm of the dish (with a cross section of 25mm x 12mm), there will be problem with fixing new LNB as it simply won't fit...:confused:

    Many thanks.
     

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    Last edited: Feb 18, 2013
  2. ant_thomas

    ant_thomas
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    It might be the most expensive option (but not exactly expensive) and a little bit of hassle but you can get a brand new dish and LNB off eBay for £18.
     
  3. pedro2000uk

    pedro2000uk
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    just move the f connector side to side for skew - the plastic outer case stays where it is & the lnb inside moves..
     
  4. wwmac

    wwmac
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    Thanks for your replies guys!

    ant_thomas - that's one of the option I am considering as well...

    pedro2000uk - I'm going to try your solution to start with, if that's going to work, it would be the most obvious one I've been missing all this time! :rolleyes:
     
  5. pedro2000uk

    pedro2000uk
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    well, if it's the one I remember, if the hole that the f connector sticks through is like a curved oblong to allow it to move ...
     
  6. wwmac

    wwmac
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    I'm pretty sure that's the shape of the hole in the cover... I will climb on the roof of my garage again tomorrow and try it out! I just need to adjust it slightly by 3º...
     
  7. logiciel

    logiciel
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    Welcome to the forum. What's wrong with the signal quality as it is now?
     
  8. wwmac

    wwmac
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    The strength and quality is satisfactory even for HD channels from HotBird with current LNB skew of -13.6°, it's just 1 channel I'm after in particular in 8PSK/DVB-S2 modulation which might require adjustment to the "proper" HB angle of -10.6° at my location.
     
  9. winston2010

    winston2010
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    A 3 degree error will not make any perceptible difference what so ever.
     
  10. logiciel

    logiciel
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    :confused:
     
  11. pedro2000uk

    pedro2000uk
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    8PSK/dvb-S2 and it's higher breakup is an increasing issue, the signal strengths may look OK but it masks that higher breakup level & thus a lower margin than it looks, IMO most Sky dishes are now a % undersized around the UK.
     
  12. wwmac

    wwmac
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    Unfortunately, the adjustment of the LNB skew did not help (as one of the members stated here last night). Pedro, in your opinion, would the upgrade of the dish to the Zone 2 60cm elliptical one help here at all (i.e. improve signal for this particular modulation)? I live in South East England. Many thanks
     
    Last edited: Feb 19, 2013
  13. logiciel

    logiciel
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    See post #2.
     
  14. pedro2000uk

    pedro2000uk
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    it's getting that way ... we've done recent tests on dvb-s2 /8psk & are revising dish sizes (up a little) - have a motorised zone 1 ready to test mainly for dvb-s2/8psk issues ..

    .... that is quite an old sky dish too so can be small & definitely smaller than we install now - the latest Raven zone 1's are 50cm on the area measure .. they were c. 45cm - some old sky dishes are smaller c. 43cm.

    so yes to a zone 2.. and new lnb not a bad idea for s2/8psk

    .. there is much claimed about dvb-s2 compliance of newer lnbs - some say there's no substance to it, don't agree 100% there tbh & in any event a newer lnb will be a % better with the small but important improvements in LNB design since those old Grundigs.

    another trick is to set the lnb in the middle of it's skew & instead skew the whole dish - it doesn't help much @ 13e tbh but further over it does - you can see a real c. 5-6% gain @ 1w if it's done right.

    what channels are they - I think one on 13e proved the highest breakup I've seen on the arc...
     
  15. pedro2000uk

    pedro2000uk
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    It was ARTE HD on 13e... on a TM5402HD it starts to break up @ just under 70% which is very high indeed ... most SD channels with an fec of 3/4 generally have a break up of c. 49% - dvb-s2/8psk is generally higher - 65% breakup is not uncommon but Arte HD is high.

    We've got it on a new zone 1 50cm Raven with a new 'sky' lnb & although the signal looks fine, it's as expected working OK on a new zone 1 @ c. 80% quality on the tm but that's only 10% margin & on a Rover meter although it shows good MER/ EVM etc.. it does warn it's MARGINAL?

    (can you tell I'm interested in this:))
     
  16. wwmac

    wwmac
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    Hi sorry, wasn't around for a while.. It is TVN HD channel that switched to DVB-S2 at 11508.00MHz, pol.V SR:27500 FEC:3/4 PID:532[MPEG-4] and I'm unable to receive since the switch to this transponder...

    Interestingly, I am receiving ARTE HD channel without any breakup via this old Grundig dish... (can't give you an exact signal quality level as my receiver is not that high-tech :laugh:, but it indicates its strength at around half-way through on the scale - which indeed is one of the lowest from the selection of HD channels I can get via this dish).

    Would you mind suggesting a good LNB to go with this 60cm Z2 elliptical dish? I've heard that Inverto are the good ones? Also, as far as I understand, not all LNBs will fit this type of dish?
     
    Last edited: Feb 19, 2013
  17. pedro2000uk

    pedro2000uk
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    TVN HD is a low power TP & combined with the fact that it's dvb-s2/8psk & that high break up characteristic which is looking like more or less the same as ARTE HD's break up - even on a new Raven zone 1 50cm there's really not much margin on TVN .

    The reason you get ARTE HD is it's basically stronger - simple as that, it's still got the same high break up issue but just a higher power to begin with & thus also higher margin overall.

    You can get it on a new zone 1 & newer lnb & if really tweaked for 13e with zero skew on the lnb & skew the dish etc. etc.. you'd maybe get some margin but a zone 2 will give you a more acceptable margin, especially equally tweaked.

    I'd use a new sky quad lnb/ middle skew & skew the dish so it thinks it's on 28e- they are very good indeed especially on motors -they miss out on the movies etc.. on 7w/7.3w 26e & a few other weak ones etc.. but otherwise you get most everything else - an Inverto BU just doesn't do that well on small dishes & there's that mismatch of the feedhorn / scala rings if used on a sky dish - we've mod'd them with the correct feedhorns but the power level threshold they perform best at is IMO above 60cm (actually, you can overload them too on a big dish:D).

    The receiver you use will make a difference too but if you got ARTE HD that sounds like it's doing quite well.


    [edit] looking for a better 'bad' example of 8psk- 11411h on 13e looks like it has an even higher ' threshold ' (better word) @ c. 73% on a tm5402hd - many would innocently assume that to be an acceptable signal but there's very little margin - it's DVB-S2/8PSK - similar in power to TNV HD but also has an FEC of 5/6 which has upped the threshold that extra c. 5%..... (an easy fix is using an fec of 2/3 which sends it the other way- the BBC have used that )
     
    Last edited: Feb 20, 2013
  18. wwmac

    wwmac
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    Thanks again for your valuable responses.

    So, are the Sky made LNBs the only ones that are really designed to work with oval dishes??

    As an alternative to Zone 2 60cm sky oval dish I reckon I could go for 80cm offset dish, however these tend to be more expensive and I'd like to avoid extra cost if possible, especially that it's just 1 channel which I am unable to receive with my current 10 years old+ sky Z1 dish ......
     
  19. pedro2000uk

    pedro2000uk
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    Zinwell quads are readily available as are Raven & Invacom zone 2 dishes & sold together - there has been more r & d etc. on these than possibly any others IMO.

    Going to an 80cm is not a bad idea & will lift the margins - it's a big jump in looks & you need a standard lnb .... then there's what is an 80 - most are nearer 70cm in the offset measure (width of reflector excl' rim) or c. 74-75cm on area (diagonal measure) & only usually 80 in height ... an 80cm on area is quite rare but a nice size for other reasons.
     
  20. kevkbuk

    kevkbuk
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