Two LNB's on H-H motorised dish to handle Optus Skew

[Fattious]

Hi Guys,

I currently have a single LNB on 90cm H-H motorised dish. I have the LNB skew mid way between 45 degrees for Optus sats and 0 degrees for the others. It picks up all sats from i701 to NSS6 with only NSS6 having some marginal BER.

I reallise there are concessions to signal strength by having the skew this way, however it does allow all 7 sats to be run of the one LNB. Symptoms of the concession are higher subjection to rain fade and inability to get reasonable signal strength on low power feeds.

As part of ongoing tinkering I am considering the merits of placing two seperate LNB's on a horizantal LNB holder arm (one with 45 degree skew, the other at 0) and switching with an A/B Diseqc switch.

Note the LNB holder arm would be horizontal. I currently use USALS so the LNB's would no longer be in the center of focus (one LNB would be each side of center). I would configure the DM500 dreambox to "go to position" rather than USALS so that the motor position compensates for the elected LNB to be centerally focused.

The dish may be just slightly off the correct elevation at the eastward and westward horizons because the motor arm would be assuming position for an azimuth that is a couple of degrees off - I think that will be very marginal tho and I could compensate that by moving the 0 degree skew LNB to the center more and move the 45 degree one out a bit further, given Optus sats have more power and the elevation will be OK at the higher observed elevations.

Even tho everything will be aligned (and hope the Universal LNB Toneburst, Diseqc A/B switching and H-H Motor all work together in practice) there should be some loss in signal due to LNB's not being placed in the optimum focal point position.

Does anyone have any opinion or better still have such a setup operational to confirm if a) this will work and b) what will provide overall best signal: compromise skew or a slightly off optimum focal point.


DM500
|
H-H Motor
|
DISEQC A/B switch
|
|-> Universal LNB at 0 degree
|-> 10.7 LNB at 45 degree


Having looked at a few forums this has been considered and appears to have been and .

It would be nice to have all 7 sats come in at 0 BER.

[beer4life]

Hi Guys,

I currently have a single LNB on 90cm H-H motorised dish. I have the LNB skew mid way between 45 degrees for Optus sats and 0 degrees for the others. It picks up all sats from i701 to NSS6 with only NSS6 having some marginal BER.

I reallise there are concessions to signal strength by having the skew this way, however it does allow all 7 sats to be run of the one LNB. Symptoms of the concession are higher subjection to rain fade and inability to get reasonable signal strength on low power feeds.

As part of ongoing tinkering I am considering the merits of placing two seperate LNB's on a horizantal LNB holder arm (one with 45 degree skew, the other at 0) and switching with an A/B Diseqc switch.

Note the LNB holder arm would be horizontal. I currently use USALS so the LNB's would no longer be in the center of focus (one LNB would be each side of center). I would configure the DM500 dreambox to "go to position" rather than USALS so that the motor position compensates for the elected LNB to be centerally focused.

The dish may be just slightly off the correct elevation at the eastward and westward horizons because the motor arm would be assuming position for an azimuth that is a couple of degrees off - I think that will be very marginal tho and I could compensate that by moving the 0 degree skew LNB to the center more and move the 45 degree one out a bit further, given Optus sats have more power and the elevation will be OK at the higher observed elevations.

Even tho everything will be aligned (and hope the Universal LNB Toneburst, Diseqc A/B switching and H-H Motor all work together in practice) there should be some loss in signal due to LNB's not being placed in the optimum focal point position.

Does anyone have any opinion or better still have such a setup operational to confirm if a) this will work and b) what will provide overall best signal: compromise skew or a slightly off optimum focal point.


DM500
|
H-H Motor
|
DISEQC A/B switch
|
|-> Universal LNB at 0 degree
|-> 10.7 LNB at 45 degree


Having looked at a few forums this has been considered and appears to have been and .

It would be nice to have all 7 sats come in at 0 BER.

G'Day Cobber,
I mooted this configuration some time ago and you seem to have given it considerable thought. Top marks.
I actually have two separate H-H dishes working fine so did not bother experimenting.
I cannot perceive any great difficulties, although it may be a bit of a fiddle.
It cannot be any wore than with the compromise of offset skews with one LNB.
Faint Heart never won Fair Lady. Go for it and I would be very interested in your results to recommend to others,
Kindest Regards, " The Druid ".

[Fattious]

Beer4life, I knew you'd bite on this one.... and know how much you detest having LNB's out of skew. I will post the signal strengths of all 7 sats before and after the experiment.

[Vlad]

I think the way that may work is if the both LNB's, either side of the lnb holder, focus on the same focal point and, as you said, don't use USALS but rather fine tune to the LNB that you will use for that particular bird.

Vlad...

[Fattious]

I'm still waiting for the Diseqc switch and arm to arrive. I have had a bit of a tweek on the current single LNB setup and have posted some results of signal strength below:

Lat/Sat/Chan/Transponder/Recording#

_______________________________1___2___3___4___5__ _6
95 NSS6 MacTV/12645V_______________________86__90__93
____AntPacific/11106H___________84__91__94
122 AS4 MacTV/12430V__________76__82__84___87___91
_____Pacific TV4______________________________________94
152 D2 NHKWorld/12544V_________86__86__60___88___89__82
156 C1 Ch7Syd/12092V___________93__90__60___93__91__96
160 D1 ABC1Syd/12513H__________94__93__88___94__96__96
166 IS8 SelectTV/12524H_________91__91__92___90__93__94
180 IS701 FranceInfo/11608H______87__89__91___84__81__85

1 = 45 Degree Skew today, note AS4 MacTV TP seems to have dropped in power
2 = 45 Degree Skew observed a month ago
3 = Zero Skew observed a month ago
Changed LNB from Acer 10600 to Strong Universal LNB
4 = 45 Degree Skew a 1.5 months ago
Changed from DM500 to DM518
5 = 45 Degree Skew of my Sydney install 2 months ago (same size dish, my original DM500)
6 = 45 Degree Skew 6 Months ago on DM500 (my original model DM500)

Most recent is recording # 1 (most recent first, then ascending to 6 being the oldest recording)

I think my DM518 (as used in 1-3) is less sensitive than my previous DM500. I think my previous DM500 is less sensitive than my first one, which would explain why #5 had the highest overall strengths.

I will add in my results of the two LNB setup when installed.

In all instances there was at least one channel with some minor BER, normally either one of the IS701, NSS6, AS4 or D1 sats. I will give my dish a wiggle to see if I am still aligned spot on the MacTV transponder as in the past couple of weeks it seems to have significantly dropped in power (and 5 digit ber).

[Fattious]

Not happy with AS4 at 82% so have made slight adjustment (moved the north axis slightly to the east of where it was and made other adjustments to suit the new placement).

_______________________________A
95 NSS6 AntPacific/11106H________91
122 AS4 MacTV/12430V__________87
152 D2 NHKWorld/12544V_________88
156 C1 Ch7Syd/12092V___________92
160 D1 ABC1Syd/12513H__________94
166 IS8 SelectTV/12524H_________90
180 IS701 FranceInfo/11608H______85

[beer4life]

Not happy with AS4 at 82% so have made slight adjustment (moved the north axis slightly to the east of where it was and made other adjustments to suit the new placement).

_______________________________A
95 NSS6 AntPacific/11106H________91
122 AS4 MacTV/12430V__________87
152 D2 NHKWorld/12544V_________88
156 C1 Ch7Syd/12092V___________92
160 D1 ABC1Syd/12513H__________94
166 IS8 SelectTV/12524H_________90
180 IS701 FranceInfo/11608H______85

G'Day Cobber,
That looks excellent. I doubt if you could squeeze much more out of it, although I have little doubt that you'll try.
One tiny anomaly, where's D3? (Actually 12092V is D3.)
Congratulations for being so thorough and posting your results to encourage others.
Kindest Regards, " The Druid ".

[viewer]

Never thought of that idea...care to post a photo whenever you get the chance?

Thanks

[Fattious]

Here are some photo's viewer.... note one LNB only still waiting on the hardware for the 2nd.

D2 (you can see the dish is bent a little in this shot)



D2 with neighbouring dish's pointing ton C1/D3




C1/D3



Compromised LNB Skew



IS701 - Couple of inches off the Stratco


NSS6


NSS6 from below

[viewer]

Thanks mate...hope your stuff gets fitted soon so I can see both on there?

[Fattious]

My Diseqc finally arrived so I have now configured two LNBs.

Optus Sats are on output A using the Grey Acer 11700 LNB, note these are pre-skewed.
Other Sats are on output B using the White Strong Universal LNB.

I have stored the 7 positions (Optus sats needed dish relocated east, other sats needed the dish relocated west). The Dreambox Rotor setup prompts to select LNB0 or LNB1 as motorised LNB, thankfully you can set both. In fact each config is unique so instead of creating 7 "go to positions" I could have just changed the latitude for each of the LNB's to account for the LNB's being off-centre but "go to positions" seems easier.

To mount two LNBs I simply took the two halves of my existing mount and swaped sides so that there were two open semi-circles allowing each LNB to be off-centre.

Below % signal strengths, first column is 1 LNB compromised skew, second column is two LNB's at prime skew.

_______________________________A__B
95 NSS6 AntPacific/11106H________88__96
122 AS4 MacTV/12430V__________86__88
152 D2 NHKWorld/12544V_________87__88
156 C1 Ch7Syd/12092V___________93__94
160 D1 ABC1Syd/12513H__________92__91
166 IS8 SelectTV/12524H_________90__91
180 IS701 FranceInfo/11608H______86__90

So conclusion is that you do get better overall signal strength.
I have zero BER on all sats.
I would think if you have a smaller dish then your two LNB results would be less favourable.

[Fattious]

Here's a picture of the setup and some more detailed ones below

[beer4life]

G'Day Cobber,
Well done.
I would however be hesitant in relying on that black foam block maintaining the correct offset when subjected to long term weather and sun.

Kindest Regards, " The Druid ".

[mtv]

I'm guessing the setup is temporary at the momemnt, but just a tip if you aren't aware...

The coloured (white & green) cable ties will perish quickly in the sun as they are not treated for UV, so you'll need to use good-quality black ties.

Also, remember to seal the F connectors on the LNB's with amalgamating butyl rubber tape to keep moisture out.

[Fattious]

MTV - Those green zip ties did well for 28 months and then, as predicted, perished. I've replaced them with black ones.

[mtv]

MTV - Those green zip ties did well for 28 months and then, as predicted, perished. I've replaced them with black ones.

An interesting test.. life expectancy will vary with weather conditions, amount of UV, etc, etc.

The black ties (and black electrical tape) contain carbon, which resists UV, prolonging their life.... (but don't tell Julia or she'll add an extra tax on them)