Slimline FTA dish Skew? (1 Viewer)

satuser165

Thread Starter
Active SatelliteGuys Member
Jul 10, 2020
20
5
South Jersey
Hello to all.......first post here!
Starting to set up an FTA system for Galaxy 19 (97W) using a repurposed dish network slimline elliptical type. Was free, so what the heck.
Have an older Viewsat 2000 I used years ago I‘m going to try and use again.
I ordered a universal LNB and a mounting bracket.
My question is this “skew” adjustment. Wherever I read it talks about rotating the LNB. I thought this was where you rotated the entire dish?
The dish pointing program didn't indicate a “skew” anyway, just elevation and magnetic direction.

Thanks for any tips!! Ken
Sewell, NJ 08080
 
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comfortably_numb

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Nov 30, 2011
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There's an LNB kit you can buy on Ebay that retrofits the Slimline for FTA:

IMG_0238.JPG
 

satuser165

Thread Starter
Active SatelliteGuys Member
Jul 10, 2020
20
5
South Jersey
Thanks for the rapid responses folks.
I ordered this 0.2dB Universal Linear Ku Satellite LNBF & LNB Single Bracket Holder Mount FTA | eBay for the Slimline.
I looked at the link above and that lna is .4db noise figure, the one I ordered with the universal bracket is .2.
Just something to play with.
Hope my old Viewsat will work with Galaxy 19. HDTV wise and all that.
Gota do something in retirement besides play with ham radio and antique radio restorations!
Ken
 
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Inclined Orbit

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Jan 2, 2018
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The DTV Slimline dish was designed and optimized to cover 20 degrees of arc with 5 LNBs pointing at different satellites, it would not be the best choice for single satellite use as I don't think you would make use of the entire reflector. With that out of the way there is no reason not to use the skew adjustment for the entire dish to rotate pol if the LNB does not have that feature. It might give you a little more adjacent satellite rejection by aligning the dish to the arc and making better use of the reflectors shape.
 

satuser165

Thread Starter
Active SatelliteGuys Member
Jul 10, 2020
20
5
South Jersey
The DTV Slimline dish was designed and optimized to cover 20 degrees of arc with 5 LNBs pointing at different satellites, it would not be the best choice for single satellite use as I don't think you would make use of the entire reflector. With that out of the way there is no reason not to use the skew adjustment for the entire dish to rotate pol if the LNB does not have that feature. It might give you a little more adjacent satellite rejection by aligning the dish to the arc and making better use of the reflectors shape.

Thanks,
Thats very interesting about the slimline but makes sense. Up above you say “rotate pol”. Dont know “pol“ means??
Decided to try a dish network 20in job I have here to start.
I put the...https://www.ebay.com/itm/361958105645 LNB in the same configuration as the original dish network lnb was.
Face is the same distance and angle from the center as the dish network lnb.
I made a small laser alignment tool. Layed the tool flat against the face of the old lnb and marked the center. Did the same with the Hypermegasat replacement. Hope that was the way to go??? >See the photo<. Laser alignment tool is that little piece wood on the other side of the arm! Has a laser diode in a hole drilled to fit it.
Thanks, Ken
 

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Inclined Orbit

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Jan 2, 2018
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If you will be looking at a linear polarized satellite as in Horizontal and Vertical polarities, you will have to optimize or null out the offending polarity with the LNB or you can rotate the entire Slimline dish. For circular pol satellites as in Right Hand and Left Hand circular there is no polarization adjustment or rotation.

The focal point of any Ku dish is critical and having the feedpoint or pickup probe off by a few mm will make a difference. The focal point would be down inside the feedhorn near the pickup probe and you could measure the original DTV LNB feed point area and match that to your new LNB, although you still could be way off.


Thanks,
Thats very interesting about the slimline but makes sense. Up above you say “rotate pol”. Dont know “pol“ means??
Decided to try a dish network 20in job I have here to start.
I put the...https://www.ebay.com/itm/361958105645 LNB in the same configuration as the original dish network lnb was.
Face is the same distance and angle from the center as the dish network lnb.
I made a small laser alignment tool. Layed the tool flat against the face of the old lnb and marked the center. Did the same with the Hypermegasat replacement. Hope that was the way to go??? >See the photo<. Laser alignment tool is that little piece wood on the other side of the arm! Has a laser diode in a hole drilled to fit it.
Thanks, Ken
 

satuser165

Thread Starter
Active SatelliteGuys Member
Jul 10, 2020
20
5
South Jersey
If you will be looking at a linear polarized satellite as in Horizontal and Vertical polarities, you will have to optimize or null out the offending polarity with the LNB or you can rotate the entire Slimline dish. For circular pol satellites as in Right Hand and Left Hand circular there is no polarization adjustment or rotation.

The focal point of any Ku dish is critical and having the feedpoint or pickup probe off by a few mm will make a difference. The focal point would be down inside the feedhorn near the pickup probe and you could measure the original DTV LNB feed point area and match that to your new LNB, although you still could be way off.
Still trying to figure out what “pol” means?? Above....
dishpointer says to set the skew at 24 degrees for Galaxy 19. I have the new LNB in the same position as the old one. Don't know whats inside! Why do they sell universal LNB’s then?
Ken
 

Inclined Orbit

SatelliteGuys Pro
Jan 2, 2018
390
215
Los Angeles
If a company sells an aftermarket LNBF specifically for a DirecTV Slimline dish, then they have probably done their homework and figured out the focal point. If its a random LNBF and random mount that happens to fit the feed arm, then good luck. Finding the focal point can be a huge time consuming science experiment even for people who know what they are doing.

An example of this is the original DirecTV KaKu dish with the side car attachment for 110 and 119. It was made by three different mfrs and you could not swap the LNBF from one companies dish to another, the focal points were all different, even for the same series dish. Fortunately DirecTV standardized the Slimline dish shape and all mfrs had to comply.

Still trying to figure out what “pol” means?? Above....
dishpointer says to set the skew at 24 degrees for Galaxy 19. I have the new LNB in the same position as the old one. Don't know whats inside! Why do they sell universal LNB’s then?
Ken
 

Inclined Orbit

SatelliteGuys Pro
Jan 2, 2018
390
215
Los Angeles
I'll see if I can relate this so it makes sense. Every linear pol satellite has a separate horizontal and vertical antenna pointed towards the earth with reference to the north and south poles of the earth. Vertical would be in line with the north and south poles and horizontal would be in line with the equator.

When looking at a satellite from earth the polarity of your ground antenna will only be perfectly horizontal and vertical with respect to your horizon when your longitude on earth is the same as the orbital slot for the satellite. For example, my longitude is 118 degrees, so a linear pol satellite at orbital slot 118W would have its antenna pointed at me exactly horizontal and vertical with respect to my horizon. The satellite orbital slot that matches my longitude will also be the highest location in the sky due south in the satellite arc at my location and orbital slots to the east and west will arc progressively downward across the sky, skewing the horizontal and vertical polarities as you get away from that orbital slot that matches your longitude.

If I point at the 123 degree orbital slot from my 118 degree longitude location vertical would be skewed to the right about 7 degrees when looking outward from the dish point of view. If I point at the 79 degree orbital slot from my 118 degree longitude location vertical would be skewed to the left about 37.5 degrees.

When you set your dish up you need to know where you are and where the satellite is so you can find out what the H and V skew will be from your horizon. Since information is transmitted simultaneously from the satellite across the same frequencies in both horizontal and vertical polarity, you need to match your antenna or LNB polarity to the satellite to avoid horizontal transmissions from interfering with your vertical reception, etc.

A way you can visualize it is draw an arc across some paper with the left and right edges low and the middle high. Make some short intersecting lines along the arc at exact right angles to the arc line to represent orbital slots. Intersecting lines near the top of the arc should be close to vertical. Intersecting lines to the far left of the paper should be tilted to the left and that would represent the skew of vertical pol. Same for intersecting lines at the right side of the paper but they will be tilted or skewed to the right from vertical.

Hope that fills in some blanks.


Still trying to figure out what “pol” means?? Above....
dishpointer says to set the skew at 24 degrees for Galaxy 19. I have the new LNB in the same position as the old one. Don't know whats inside! Why do they sell universal LNB’s then?
Ken
 
Last edited:

Brct203

SatelliteGuys Pro
Dec 24, 2016
1,175
1,149
Connecticut
pol=polarization, or polarized
as InclinedOrbit explained, it has to do with the geometry of the radiowaves
long story short, sites such as dishpointer will tell you the "skew", it's the angle by which you need to retate the LNBF - or the entire dish (in which case the LNBF can have a skew of 0 degrees) - the result is the same.

a note about "universal" LNBF and LNB. It has nothing to do with how they mount and whether or not they fit a specific dish. It's all about the frequency range that they cover. The KU band for TV services goes from 10700 MHz to 12750 MHz. It is further subdivided in 3 bands (in the context of North America):
10700 MHz to 11700 MHz: used by some international satellites, some of which can be received from parts of the US, but definitely not the most popular band.
11700 MHz to 12200 MHz: that's the main Ku band used for FTA services in the US. That's where the action is. That specific band is often referred to as "standard".
12200 MHz to 12750 MHz is used by pay TV like Dish Network, DirecTv and their Canadian cousins. Those typically use circular polarization and are not directly compatible with regular LNBFs (but you will occasionally scan in a bunch of encrypted channels from those satellites)

so a Universal LNB or LNBF covers those 3 bands
a Standard LNB or LNBF covers only the middle one, 11700 to 12200 MHz. It's more limited but in most cases that's all you need. It will usually allow for faster blind scans (since there's a lot less to scan)

from your location (NJ) there are 2 satellites with services in lower band Ku (10700 to 11700) , one with TV from Guyana, and the other one with a few French TV and radio channels.

That 20" Dish Network dish is definitely small, but should be enough to get a few channels. Just expect to lose reception when there's rain or snow.

the easiest target to start with is Galaxy 3C at 95W, with the CGTN channels. Once you get that, you can fine-tune the LNBF position. Then move the dish slightly toward the west, and you should find 97W.

now, because that dish is small, it will get interference from adjacent satellites. This is a problem with 97W because it's neighbors are a bit more powerful. You might find that some transponders are hard to get, while others are fine. Only a larger dish will solve that. Even the slimline might be too small to avoid such interference.
 

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