Dual Polarity 3 LNB

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Samoaga

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Oct 20, 2005
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Vaitogi, American Samoa
Attached is a photo of a system I just put together. I have not tried it yet. Do you think it will work? I am going to test it on Intelsat 19, using a 3.8M offset.
 

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Brct203

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Dec 24, 2016
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I’m not sure I understand what it is you are trying to achieve... are you trying to do linear on one LNBF and circular on the other?

I don’t think that would work, as each port of the orthomode feed would get only one polarity.
 

pacificrim

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I'm pretty sure you would do better with just the conical scalar and the dual C/Ku.
A 12.5 ft offset is huge and it should do well. But since you built it - try it! Let us know!
 

Samoaga

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Oct 20, 2005
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Vaitogi, American Samoa
I’m not sure I understand what it is you are trying to achieve... are you trying to do linear on one LNBF and circular on the other?

I don’t think that would work, as each port of the orthomode feed would get only one polarity.
Well, what I was trying to do was get two H/V C band feeds and one Ku H/V band feed on two cables. You were the closest on predictions. One C Band H/V LNB did not work at all and the other would only work on only one polarity. So far I have had no joy with Ku band, but not many get to this rock and I have not stopped trying yet. I am not familiar with the Ku specifications of my LNB or what control signals are necessary, and have been trying different combinations. On reflecting why the second C Band did not work at all I realized that the C-Band splitter selects only one polarity and passes the other polarity to the second LNB, which is what your response confirmed. It was aligned to the the incorrect polarity. I turned it 90 degrees and got a signal. I would not call the experiment a failure but definitely a learning experience. I had presumed that the C-Band splitter would send the full band and the alignment of the LNB would select H/V. Right now I have the C/Ku unit only on my dish and it works fine on C-Band, zilch on Ku.
 
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Brct203

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Indeed, in this type of feedhorn, I think the LNB that is directly aligned with the feedhorn has its polarity set by the shape of the tube, as it transitions to rectangular. and if you look inside you see a little metal thing encased in plastic (that thing is really an antenna) that transports the other polarity signal to the second LNB opening.
As for the C/KU combo LNBFs, I had the opportunity to try one on an 8-foot dish, and all I could get was the strongest transponders, such as CGTN on 95W, and JBS on 99W. From what I understand it's basicaly a C-Band LNBF, and they made a hole at the end and mounted a Ku LNBF. But the built-in feedhorn is really tuned for C-Band and the Ku LNB gets limited signal. From what I read, it works fine on some dishes and really poorly on others.
Instead, on my 10-ft dish I attached a cheap Ku LNBF to the side of the C-Band scalar, and it's working quite well. Of course one drawback is that Ku- and C-Band are not aligned, so that's many more entries in the positionner. (I also added a circular polarization feedhorn on the opposite side of the scalar)
 
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Samoaga

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SatelliteGuys Family
Oct 20, 2005
42
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Vaitogi, American Samoa
Indeed, in this type of feedhorn, I think the LNB that is directly aligned with the feedhorn has its polarity set by the shape of the tube, as it transitions to rectangular. and if you look inside you see a little metal thing encased in plastic (that thing is really an antenna) that transports the other polarity signal to the second LNB opening.
As for the C/KU combo LNBFs, I had the opportunity to try one on an 8-foot dish, and all I could get was the strongest transponders, such as CGTN on 95W, and JBS on 99W. From what I understand it's basicaly a C-Band LNBF, and they made a hole at the end and mounted a Ku LNBF. But the built-in feedhorn is really tuned for C-Band and the Ku LNB gets limited signal. From what I read, it works fine on some dishes and really poorly on others.
Instead, on my 10-ft dish I attached a cheap Ku LNBF to the side of the C-Band scalar, and it's working quite well. Of course one drawback is that Ku- and C-Band are not aligned, so that's many more entries in the positionner. (I also added a circular polarization feedhorn on the opposite side of the scalar)
I tried the combined C/Ku feed and picked up the C-Band AFRTS encrypted transponder on the dateline Intelsat, but got no Ku. I decided to take the Ku LNB out of the combined unit and and try it on its own. I mounted the LNB in the C Band Feedhorn, at its focal point, so I could easily rotate it to the correct polarization. I got the strongest signal I have ever received here 13.7 C/N. I attached a cable and did a blind scan and picked up 64 Ku TV channels. I think they were all French and most were encrypted. Tomorrow I want to try the same Ku LNB at the focal point of my offset 3.8M dish on Intelsat 19. The photo shows the Ku LNB mounted with packing foam inside the offset scalar feed, ready for the test.
 

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Brct203

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Dec 24, 2016
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I tried the combined C/Ku feed and picked up the C-Band AFRTS encrypted transponder on the dateline Intelsat, but got no Ku. I decided to take the Ku LNB out of the combined unit and and try it on its own. I mounted the LNB in the C Band Feedhorn, at its focal point, so I could easily rotate it to the correct polarization. I got the strongest signal I have ever received here 13.7 C/N. I attached a cable and did a blind scan and picked up 64 Ku TV channels. I think they were all French and most were encrypted. Tomorrow I want to try the same Ku LNB at the focal point of my offset 3.8M dish on Intelsat 19. The photo shows the Ku LNB mounted with packing foam inside the offset scalar feed, ready for the test.
that's cool! Looks likely that you're getting the Canal Calédonie package that's aimed at New Caledonia and at Wallis and Futuna islands (just like we're getting Canal Caraibes from here).

I checked your location on SatStar.net, and it looks like you might also be able to get some Ku stuff on 152E (JCSAT 2B) - but i don't know if there's any content there.

As for Intelsat19, looks like you might be outside its Ku beams, but it's certainly worth a try. The small scalar on your Ku LNB might not work so well on an offset dish.
 

Samoaga

Thread Starter
SatelliteGuys Family
Oct 20, 2005
42
1
Vaitogi, American Samoa
I tried the Ku LNB in my 3.8M offset dish. No signal. I then tried it in a 1.5M dish in case it was just a focal length problem. Still no joy. Today I am going to look at 172B on a 5M dish for a C-Band signal I want to get from PNG. Unfortunately my spectrum analyzer was lost by Satlink when sent back for warranty repair, otherwise I could tell whether a signal is present but just too weak to lock. I keep hoping that SatLink will recognize their responsibility and replace the lost unit, but I may have to purchase another one. Satlink took a long time to "repair" my unit and asked me to be patent because it was the Chinese new year. 3 months later they sent me a tracking number which said the unit was in transit. It was still in transit 3 months later after which the tracking site became extinct. The next Chinese New Year is just around the corner.
 
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