c band lnb rotation.

[manuelpaz]

Hi all

I wonder from satellite 55w or 58w the c band lnb stay in the same posotion (no move the lnb) but now if i move the c band dish from 58 w to satmex6 ,do I have to rotate the c band lnb to the right or left or just leave it there.

I really thank u for any comments about this Satmex6.

 

[hd fan]

OK I think the mod should merge and create a unique thread then.

As a matter of fact for optimal reception you should rotate or skew the LNB always , for linnear SATS (H and V polarization) only. Of course 55 and 58 being so close , they will work without adjusting the LNB. For SATS west of your longitude , rotate clockwise from behind the Dish , and viceversa. check dishpointer.com for proper values of Skew for any bird.

Every 33 degrees of skew is 5 minutes on the face of a watch , 90 degrees are 15 minutes.

 

[Mr Tony]

check Satellite Angle Calculator - SatelliteGuys.US above
enter your zip or city/state and it will tell you the skew for each satellite

skew for each location is different depending on what longitude you are at. I am at 93W so 89/91/93/95/97 is almost the same skew across the board so I really dont need to adjust skew. But anything off that then I really need to adjust skew

proper skew adjustment = signal

 

[B.J.]

I'm confused by the responses to this question. Seems like before answering, one should ask whether the OP has an Az/El mount or a polar mount, and I may have missed it, but I don't think the OP said what he had. Ie if the dish is on a polar mount you don't change the skew of the feedhorn when moving from sat to sat, but the responses seem to be assuming that he has an Az/El mount?

 

[hd fan]

but now if i move the c band dish from 58 w to satmex6

I assumed that by If I move , the OP meant that he acctually moves the Dish himself like I do since I do not have an actuator or motor yet. More likely if the OP had a motorized setup he would have not asked this question since the Dish would have worked fine or would have used the word rotate. It is more likely that, like me, he has a polar mount without an actuator yet.

BTW BJ, I am also assuming that by Polar mount you mean a motorized setup and by Az/El you could also mean the same mount but without some kind of motor, Am I right or right? , lol.

Sellers sell 2 kind of C-Band mounts , Stationary and the Polar version, both of which out of the box could be called Az/El mounts since the Polar version does not come with an actuator arm. I just loosen the screws on the base of my mount and then rotate the dish on its pole to adjust the Az, therefore the need for Skew Adjustment for linnear Sats.

At the end BJ I agree with you, we should have either ask the OP or just mention the fact that motorized setups do not need skew adjustment. Man , after all this talk , now I want to get an actuator for mine!, lol.

 

[hd fan]

OH OH. I think I have a big misunderstanding of how the polar mount works and/or differences with the Az/EL Mount.

I am about to motorize my FS 6 footer with an arm actuator , 24 inches more likely. I will use the Gospell C/Univ Ku LNB. It is my understanding that as the arm extends the dish will not only rotate to get the proper azimuth but also will skew itself accordingly thanks to the declination setting probably therefore I will not need a servo based skewable LNB?.

Am I right? After playing manually with several extreme sats and seeing how big the skew , I am not so sure the Dish will skew itselg with the arm only like the samll Ku dish with the H-H motor. Or does it skew itself?

 

[hd fan]

ok after re-reading the C-Band FAQ I cleared my thoughts again. It is just that after playing today with the extreme sats and skewing manually for some reason I thought the actuator arm was not enough. but my polar mount is fixed therefore it a has a fixed plate attached that forces the dish to have 11 degrees of declination offset instead of the 6 or 6.7 that will have when the arm is installed. BTW as per some online sources the declination offset is 6.7 for 43.6N but as per a chart posted here it is 6 for 43.5 and 44N respectively. I wonder if the chart is inaccurate for around 44 degrees latitude.

 

[Anole]

For general info, use this page:

Footprints by Dish Size - Adjusting the Polar Mount for Prime Focus Antenna - C/Ku-Band Satellite Systems - Tuning, Tracking, Azimuth, Elevation, Declination Angles, F/D Ratio, Focal Distance, Inclinometer, LNB/Feedhorn Assembly, Actuator Assembly, C


I like the modified declination chart at the bottom of this page:

Footprints by Dish Size - Latitude Declination Chart - C/Ku-Band Satellite Listing

edit: oops, I had the links reversed... should be okay now.

 

[hd fan]

Thanks Anole. Now I see why there are 2 kinds of charts. 1 for the polar mount used by astronomers and the other one , the modified polar mount , used by us for satellite dishes. Therefore both are accurate depending the aplication. Dishpointer.com for instance for the true south parameters list 6.7 declination offset for my latitude consistent with the astronomers polar mount and they use the latitude as the elevation value. Valid for H-H motors BTW. IMHO for true south info they should have shown the modified parameters as per the chart you posted since normally a user with a H-H motor will select the type of motor directly from the drop down menu.

 

[Anole]

I'm talkin' BUDs:

Since we've never been able to set the numbers perfectly, I suspect either table is a good place to start.
Then, you dial it in by hand, depending on your experience.

Today, with very accurate digital inclinometers, you -can- set the declination right on the money and never touch it again.
Any error in the mount, is then tuned out by adjusting elevation.
And you have fewer variables to juggle, while fine-tuning the dish.

Expecting to accurately measure everything and have it all work right off the bat, is silly.
Chance are high, that there is some error (lnb off center? ) so you always have to do the final tweaks.
I'm sure professional installers come very close on the first try!
Most of us tune up two dishs (BUDs) ever, and never get that professional experience.
. . now if we did five BUDs a week . . . just imagine how easy it would be! -

 

[B.J.]

...

BTW BJ, I am also assuming that by Polar mount you mean a motorized setup and by Az/El you could also mean the same mount but without some kind of motor, Am I right or right? , lol.

Sellers sell 2 kind of C-Band mounts , Stationary and the Polar version, both of which out of the box could be called Az/El mounts since the Polar version does not come with an actuator arm. I just loosen the screws on the base of my mount and then rotate the dish on its pole to adjust the Az, therefore the need for Skew Adjustment for linnear Sats.

........

Well, generally, an Az/El mount doesn't have the ability to be a polar mount, as there is generally no way for it to move if you attach an actuator. But you are right, that if you somehow lock a polar mount at the top of it's rotation axis, then you could use the latitude / inclination adjustment as elevation , and rotate the whole mount on the pole for azimuth. It would function as an Az/El this way, but it's still a polar mount. A real Az/El mount will never be a polar mount, however. It needs to have a rotation axis nearly parallel to the earth's axis to be a polar mount, and Az/El mounts are on a vertical pole.... no way to rotate around a polar axis.

OH OH. I think I have a big misunderstanding of how the polar mount works and/or differences with the Az/EL Mount.

I am about to motorize my FS 6 footer with an arm actuator , 24 inches more likely. I will use the Gospell C/Univ Ku LNB. It is my understanding that as the arm extends the dish will not only rotate to get the proper azimuth but also will skew itself accordingly thanks to the declination setting probably therefore I will not need a servo based skewable LNB?.

Am I right? .....

Correct.

ok after re-reading the C-Band FAQ I cleared my thoughts again. It is just that after playing today with the extreme sats and skewing manually for some reason I thought the actuator arm was not enough. but my polar mount is fixed therefore it a has a fixed plate attached that forces the dish to have 11 degrees of declination offset instead of the 6 or 6.7 that will have when the arm is installed. BTW as per some online sources the declination offset is 6.7 for 43.6N but as per a chart posted here it is 6 for 43.5 and 44N respectively. I wonder if the chart is inaccurate for around 44 degrees latitude.

I think your 6.7 vs 6.0 declination question was answered, but I'm confused about the 11 deg declination comment above. There will NEVER be a need for 11 degrees of declination. Even if you were at the north pole, the declination would only be about 8.6, and you can't even see any geostationary sats from there anyway, so even that declination isn't something that would be needed. Declination is a term that is only applicable if your dish rotates around an axis parallel (or nearly parallel as is the case for the modified declination method) to the earth's axis. You aren't doing that, so you aren't using declination by any stretch of the definition I can think of. You just have an elevation that is some strange combination of the mount inclination and the position you happened to lock the polar axis into.

 

[hd fan]

yeah I know BJ, it is just that since I assembled the Dish I have not played with the declination offset adjustment mostly because the fixed plate will not allow me to adjust it properly. I did not have an inclinometer either. I have not tried to adjust it and I even thought that I assembled the Dish somehow the wrong way the first day but I wanted to wait untill the day that I had to install an actuator. I will have to take pictures so you guys can tell me if it was wrongly assembled.

The point is that , the fixed plate , the way it is installed now (grabs the dish closer to the center) forces this declination to be 11 degrees. Like you said since my dish is stationary for now (no actuator), I do not need this declination , I just adjust the total elevation to the proper value, mount inclination + 11 in this case. before the inclinometer, it was me standing to the side of the dish and drawing a 90 degrees angle and dividing it by half untill necessary in the air , lol, the so called cuban inclinometer lol, forget the poor's man soda version that you guys posted here, that one it is still too expensive , lol.

I am glad you have replied to my posts and that I decided to talk about polar mounts since it forced me to search more about it and together with your valuable input now I have a better understanding of it. I will try this weekend to set the mount to true south and set the declination properly to my 6.7 value but I am afraid that I will have to change the length of the fixed plate for that. Like I said, on this FS 6 footer , the fixed plate that comes with the polar mount forces the Dish to be grabbed in 3 positions only (there are 3 holes on the horizontal bar only). BTW , this dish will only allow someone to do a West ARM installation since there are no holes on the horizontal bar to the left of the dish. It is ok for me since I live east of the Mississippi. And because the plate is fixed in length, that results in a fixed declination offset angle. You guys with actuators can lock the declination offset first and then move the actuator clamp accordingly probably. Besides if I remove the fixed plate alone , the Dish will "fall" rotating over the polar axis. I need that plate for now to lock the dish in place.

Now that I think about it I will have to revisit the whole assembly of the Dish carefully again, just in case. I am about to pull the trigger on motorizing my Dish so that revision is coming anyways.

Once again thanks for your valuable comments.