Skew on AMC1 Ku, my observations

[delta_charlie]

Hi all, I wanted to try and see if I could pull in the DVB-S2 NBC feeds on AMC1 so I tried the fixed 76 CM dish I have set up for the Pentagon channel with my AZbox but could not find anything. On a hunch I decided to try my WS9036 and got a lock. After a bit of cross checking I'm thinking only some of the TPs on AMC1 have skew that is off from normal. Looks like it may only be the vertical TPs that have the weird skew.

Anybody else notices this?

Here is a bit more info on my setup - the fixed 76CM dish has the LNB skew peaked on the vertical TP for the Pentagon channel. The WS9036 is mounted on a motor so the skew is set by the movement of the motor so when I moved it over to AMC1 the skew would have been normal. All the horizontal TPs I checked seemed to be quite a bit stronger on the WS9036 then the 76CM (more of a difference then just the size of the dish would account for I think)

Got to run, DC

 

[rocco_fanucci]

try a 26 deg. CCW offset

 

[B.J.]

Hi all, I wanted to try and see if I could pull in the DVB-S2 NBC feeds on AMC1 so I tried the fixed 76 CM dish I have set up for the Pentagon channel with my AZbox but could not find anything. On a hunch I decided to try my WS9036 and got a lock. After a bit of cross checking I'm thinking only some of the TPs on AMC1 have skew that is off from normal. Looks like it may only be the vertical TPs that have the weird skew.

Anybody else notices this?

Here is a bit more info on my setup - the fixed 76CM dish has the LNB skew peaked on the vertical TP for the Pentagon channel. The WS9036 is mounted on a motor so the skew is set by the movement of the motor so when I moved it over to AMC1 the skew would have been normal. All the horizontal TPs I checked seemed to be quite a bit stronger on the WS9036 then the 76CM (more of a difference then just the size of the dish would account for I think)

Got to run, DC

It is well known, and has been posted hundreds of times, that the Ku polarity is off by ~26 deg on AMC1. There have been several "theories" about why, including some anomoly or malfunction at launch time, and I've read several places theories to the effect that it was intentional in order to make it easier for people in NYC to install their dish with the feeds vertical instead of skewed. I don't know which theory to believe, but I do remember that when that sat went up, that not only was the Ku skew off on it, but they had another GE sat right next to it, either GE4 or GE2, which also had it's skew off by the same amount, but then later that other sat reverted to normal skew. So it's interesting, and I don't know why they do it. It's not an issue with feedhorns with a polarotor, as you can fine tune the skew, but with LNBFs that have fixed skew, it's a problem.

 

[Mr Tony]

An uplinker once explained what happened with AMC1
SatelliteGuys.US - View Single Post - New Member: an uplinker

a fixed dish at 103W with the polarity skewed "properly" brings in way more signals

 

[Babadem]

An uplinker once explained what happened with AMC1
SatelliteGuys.US - View Single Post - New Member: an uplinker

a fixed dish at 103W with the polarity skewed "properly" brings in way more signals

......based on the odd skew which is the best frequency to use when peaking the dish?

 

[B.J.]

An uplinker once explained what happened with AMC1
SatelliteGuys.US - View Single Post - New Member: an uplinker

a fixed dish at 103W with the polarity skewed "properly" brings in way more signals

Yeah, I've read that explanation, but that one makes less sense than any of the other explanations I've heard, none of which really make complete sense. Ie if the whole satellite were "tilted" as he says, then C-band would be off too, but it's not. And the theory about making it easy for the network dish installers in NYC doesn't make sense, even though that came from people in the industry too. I might believe that they lost control of polarity on Ku, but why would it affect all transponders, unless perhaps all the Ku transponders are on the same mechanism somehow, plus, you'd think that if they still had control of C-band, then they could just tilt the whole sat, and bring C-band back into the proper skew, unless maybe the C-band polarity is done by tilting the whole sat.
It just seems odd to me, no matter what explanation I hear.

 

[Mr Tony]

......based on the odd skew which is the best frequency to use when peaking the dish?

start with 12100 V 20000 (Pentagon)
I have used 12117 H 4232 which is a test card that is usually up 24/7

The issue seems to be the vertical side stuff registers fine with either the "right" skew or the "wrong" one (wrong being a motorized)

Lots of NBC news feeds between 12000-12200 Horizontal

 

[delta_charlie]

Hi all, and just to make it seem even more strange I can only get the NBC DVB S2 feeds on my WS9036 that has normal skew. My fixed dish that has the skew peaked on the Pentagon channel does not pull in the S2 feeds.

???

Later, DC

 

[guacharaca]

I suspect that size of the dish is the most significant reason. All thoses horizontal NBC feeds are weak signals and can not be received in BC on a one meter dish. Only on the 1.2 meter dish they show up. The S2 signal required even additional tweeking of the lnb to get a constant signal (HD + S2 = big dish).
I wish I could tell if it was 20 or so degrees out from verticle, but this lnb only does one plane at a time so I can not switch back and forth to see the signal on vertical. I have to manually rotate the lnb 90 degrees. Thanks for starting this thread because I was previously unaware that all those horizontal tps were actually being used because the signals are too weak for my motorized dish.

 

[LocutusOfBorg]

Does it matter adjusting skew using AMC1 with a Birdog or should I move to SES1 or AMC18 to adjust skew? AMC1 is my true south sat.

 

[DJ Rob]

If using KU and wanting to adjust skew, I would try a different sat like 101 or 105

 

[Mr Tony]

Does it matter adjusting skew using AMC1 with a Birdog or should I move to SES1 or AMC18 to adjust skew? AMC1 is my true south sat.

C-Band ro KU?

C-Band its the correct skew
KU you can use a TP on the vertical side. They seem to be better (higher quality) even with the "wrong" skew (ie: in your case 0 skew)

 

[LocutusOfBorg]

C-Band ro KU?

C-Band its the correct skew
KU you can use a TP on the vertical side. They seem to be better (higher quality) even with the "wrong" skew (ie: in your case 0 skew)

C band. Thanks.

 

[Mr Tony]

C-Band is the normal skew so you shouldnt have to worry about it

 

[Hindu55]

I think guacharaca is right on about the size of the dish. I just went out and
moved the skew close to where it should be on my motorized 76cm Winegard
and the Q jumped way up on the Pentagon channel. I did a scan and only
picked up one of the S2 feeds and it was near threshhold. I got them all on
my motorized 90cm with the skew left at 0 (normal). I know I've adjusted the
skew on the 90cm for that sat in the past and they jumped way up in Q. S2
just takes a healthy signal. The S2 Florida channels on AMC 3 are the same
way. I don't get a sniff on the 76cm but get them fine on the 90.