LNB Skew for Dual-Feed Multi-Satellite Dishes
A dual-feed dish can receive two satellites without installing a second dish, but it gives the installer two slightly different pointing geometries. Each feed horn sits at a different angle, and each geostationary satellite has its own orbital longitude, azimuth and elevation. Dish alignment is only half the job; LNB rotation must also suit the satellite passing through each horn.
LNB skew is the rotation of the low-noise block’s polarisation axis, often called feed horn roll. It is not the tilt of the dish face. On a linear-polarised link, incorrect skew can weaken the wanted transponder, invert horizontal and vertical channels, or cause a picture that looks locked but breaks up in rain. Circular-polarised signals require a different approach.
Using SatPointer to calculate the proper LNB skew for a dual-feed multi-satellite setup works best as a measured sequence. Enter the precise installation location, obtain the pointing data, then relate each satellite’s orbital position to the physical zero position of its LNB. The dish geometry and chosen feed assembly still have to be considered.
That distinction matters in Australia. Sydney, Melbourne, Brisbane and Perth occupy widely separated longitudes, while Optus and Foxtel reception commonly uses circularly polarised Ku-band signals. A backyard pole or balcony installation also brings metal roofs, trees, nearby power lines and limited access into the adjustment process.
Why skew differs between satellites
Skew changes because the satellites are not in the same place in the sky. A geostationary satellite above 153°E and one above 164°E present different azimuths and elevations to a dish in Melbourne. Their apparent east–west movement also crosses each feed horn differently, so a skew value for one satellite should not be copied unchanged to the other.
A multi-feed dish adds its own complication. Offsetting each LNB from the dish centre creates a feed-arm or squint angle. The ideal rotation measured in the sky is therefore not always identical to the number printed on an LNB clamp. Accurate installation depends on knowing whether the manufacturer measures from vertical, the feed-arm axis or the clamp’s zero mark.
The SatPointer overview describes SatPointer, a free web-based tool operated by TotalSat Limited that combines Google Maps, orbital data and a selected location to produce pointing directions for reception, uplink, downlink and mobile satellite links. That provides the orbital reference and main dish angles. The physical skew setting still comes from the geometry and mounting instructions.
Finding pointing angles for each feed
Start with the actual address, not merely the nearest town. Enter each intended satellite in reception mode and record its azimuth, elevation and orbital longitude. Google Maps confirms the site reference, while satellite beam-coverage and estimated dish-size information helps assess whether the selected satellite is practical there.
Azimuth runs clockwise from true north; elevation is measured above the horizon. Treat both as dish coordinates, not LNB settings. For a two-satellite installation, save both targets before moving the mount. Deciding the second target only after installing the first feed makes small errors harder to correct.
A steel roof, screen or nearby building can make a compass reading unreliable. SatPointer’s compass-free azimuth method provides a practical way to establish the initial direction without relying on a phone’s magnetometer. Check it against a fixed compass reading where possible, since a handheld compass can also be affected by the dish and nearby metal.
Use the coordinates to choose a position with clear line of sight for both feeds. Mark the primary dish axis and secondary-feed axis, then check both against obstructions. It is easier to alter a mark on a pole than to rotate a fixed dish, loosen a bracket or move a ladder after installation.
Calculating skew from SatPointer pointing data
The orbital longitude offset, Δ, is the difference between the satellite’s orbital longitude and the installation longitude. Use signed degrees in the same direction for both values. Required rotation is a function of that offset and calculated elevation, because elevation changes how much the orbital arc appears tilted to the installer.
A useful starting formula is S = arctan[tan(Δ) ÷ sin(E)], where S is ideal skew, Δ is the orbital longitude offset and E is elevation. Keep the calculator in degrees and preserve the sign until applying the manufacturer’s rotation convention. This is a geometric reference, not a reason to turn both LNB clamps by the same amount.
- Record the site longitude and exact installation point in SatPointer.
- Look up each satellite and note its orbital longitude, azimuth and elevation.
- Calculate Δ for each target, then apply the formula using that target’s elevation.
- Convert the result to the LNB’s physical zero reference and record the rotations separately.
For example, an eight-degree orbital offset with an elevation of 40 degrees gives an ideal rotation of roughly 12.3 degrees. Recalculate when the actual elevation differs. On a twin-LNB arm, set the primary LNB at its specified reference, position the second arm, then fine-tune the second rotation by signal quality.
Setting the feed arms and protecting the primary signal
Fit the mast securely and route the coax before setting the fine skew. The LNB angle can change when the clamp is tightened or cable loads the arm, so support the horn gently during adjustment. A stable reference plane is more valuable than a perfectly rotated LNB on a bracket that later moves.
Align the main dish with the primary satellite’s SatPointer azimuth and elevation, then secure it. Set the primary LNB to the calculated rotation using its manufacturer’s zero mark, and confirm the wanted channels before touching the secondary arm. On a linear-polarised link, a 90-degree error swaps the horizontal and vertical components and can look like a tuning fault.
Bring the second feed arm to its own target. Its required skew may differ by several degrees, but the arm can also introduce a cross-polarisation component that affects the primary satellite. After moving it, recheck the main picture and receiver quality readings, then make the smallest adjustment that restores both targets. A compromise position may be needed on a compact assembly.
A single-LNB dual-output horn is not two independent feed arms. It uses a combined feed structure and may rely on switching or combining prescribed by the manufacturer. It has one physical rotation, and changing it can affect both outputs. Follow the model-specific instructions instead of applying two calculated values to one clamp.
Practical checks for Australian installations
Australian conditions make verification worthwhile. Many domestic systems sit on a backyard pole, terrace wall or Colorbond roof, often near trees that later grow into the signal path. Regional viewers may use VAST, while Optus and Foxtel installations use circular polarisation. Confirm the service and feed specification rather than assuming every Ku-band LNB needs skew rotation.
ACMA administers spectrum licensing and operating rules for commercial and amateur satellite services. Household reception is separate from authorising a transmit link, but anyone using SatPointer for uplink, downlink or mobile operations must check the relevant Australian licence and technical conditions. Clearly label receiving and transmitting configurations.
- Confirm each satellite’s orbital position, beam coverage and polarisation.
- Check calculated azimuth and elevation against the physical line of sight.
- Verify the LNB clamp reference, cable routing and weatherproof connections.
- Record primary and secondary settings before final tightening.
Save receiver signal-quality readings for both feeds and compare them in clear and overcast conditions. Freezing during a coastal shower can indicate skew error, imperfect alignment, water ingress or marginal coverage rather than a failed receiver. When documenting a repair for a customer or installing club, reference material standardised through HD video conversion can preserve before-and-after observations.
Final verification and next steps
Use a short comparison sheet for the final check. It should show that each feed has a distinct pointing target while retaining the physical offsets required by the dish design. SatPointer supplies the location-based coordinates and orbital references; the receiver and installer’s meter supply the evidence that the rotations work.
Fill in the values from your own setup. The azimuth, elevation and orbital position must belong to the same satellite in each row, while the LNB rotation reflects that feed’s physical zero position. If the second satellite is stable but the primary has weakened, revisit the arm position and main-dish compromise before replacing equipment.
| Check | Primary satellite | Secondary satellite | Verification |
|---|---|---|---|
| Orbital longitude | SatPointer value | SatPointer value | Different values justify separate skew calculations |
| Azimuth | Main-dish target | Second-feed target | Both lines of sight remain within the feed geometry |
| Elevation | SatPointer value | SatPointer value | Match each calculation to its own satellite |
| LNB rotation | Calculated and measured | Calculated and measured | Apply the correct zero mark and sign convention |
| Signal quality | Receiver reading | Receiver reading | Stable pictures with some weather margin |
Open SatPointer with the exact site coordinates, save both satellite targets and check beam coverage and estimated dish size before ordering or mounting hardware. Installers and enthusiasts can also embed a customisable SatPointer widget on a website, blog or forum, giving visitors location-specific pointing information without rebuilding the calculation.