How Bad is Too Bad?

[cyberham]

I'm doing the string test on my 1.2m Ku dish that hit the ground hard two times from wind storms recently.

The long axis (vertical) string is 2.5 inches above the short axis (horizontal) at the center. Bad, huh?

Will it work at all?

I've been playing all day and I can't lock any sats. Closest is KBS on 123W. I get 7 to 10% SQ, but no lock. In past, this tp was very strong at 80%.


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[Titanium]

The strings should be lightly touching. 2.5" difference equals a taco shell, not a parabola. A taco shell does not reflect signals to a single sweet spot!

With all hardware removed, lay the dish face down on a perfectly flat surface like a glass table or known flat concrete floor. Mark the two edges that are contacting the flat surface.

Pick up the reflector and stand behind the reflector and grabbing the edges of the reflector like a steering wheel. Hold the dish at the two marked locations. Make a forward thrusting movement like passing a basketball. Lay the dish back onto the flat surface and observe if laying flat. If not, repeat until corrected then remount the hardware.

 

[cyberham]

Sounds like I have a date with my garage floor. I'll try it. It can't get any worse.

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[N6BY]

I also had a warped 1.2 meter dish. I tried and tried but could not restore it to work as well as new. It was a sad loss. I could get another one locally for around $120 from SatelliteAV and not pay shipping. But I'm wondering if it would also warp like the first one?

I hope you have better luck.

 

[a33]

See also here:
Is this considered warped?

Greetz,
A33

 

[cyberham]

I have successfully shaken my bent dish so the string test is now much better. The strings are almost touching. The dish looks much better overall. Now to mount the dish inverted since 125W is 11 degrees elevation and see if I can lock it.

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[cyberham]

The shaken dish can now receive all sats 87W to 105W with SQ at normal levels except the NBC mux on 103W. Not sure why that is so difficult but NBC and COZI just won't lock in. I can receive all other tps on 103W including the NHK mux at good level.

The dish is right at ground level now mounted on a wooden pallet. The LNB arm is 1 inch above ground. Would this play into making NBC difficult? Is there such a thing as ground noise? Or maybe the dish is still not quite the original shape.

Next is to invert the dish so I can continue the journey westward along the arc en route to the real target of 125W. KBS on 123W should be easy then it's just a bump west to PBS through the trees and at 11 degrees elevation.

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[N6BY]

...
The dish is right at ground level now mounted on a wooden pallet. The LNB arm is 1 inch above ground. Would this play into making NBC difficult? Is there such a thing as ground noise? Or maybe the dish is still not quite the original shape....

I think that being close to the ground may increase multi-path problems and noise from other satellites, since there will be signal reflection coming from below. But I have never measured how much this can affect reception.

And as I sadly admitted in post #4, on my 120 cm GeosatPro dish I tried and tried, but never could restore the exact shape. I couldn't even get it to perform as well as a 90 cm dish. So I had to discard it. I still have its "naked" mounting pole in the ground, waiting till I am brave enough to try my luck with another 120 dish. Wish they came with a lifetime guarantee against warp. Otherwise its a very expensive hobby.

 

[cyberham]

Satbeams shows footprint here of 103W as 44 dBw needing 90 cm dish. Whereas 125W is 46 dBw with 80 cm dish recommended. For comparison, 87W is 48 dBw with 70 cm recommended and 99W is 49.4 dBw with 65 cm.

This means 103W is weakest of all. So maybe my results make sense.

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[cyberham]

Is there any way to constructively combine signals from two different dishes? Or is there an economical satellite signal amplifier as I have for my OTA antenna? A small increase in signal from 103W would likely make it watchable.

 

[N6BY]

At KU band frequencies the wavelength is about 1 inch. So the signals reaching the two dishes would have to be almost exactly the same distance from the satellite -- maybe within 1 mm of each other? Also would need the same distance of coax from the LNBFs to the combiner. Otherwise the phase mismatch would cause the waves to cancel each other out.

There is, of course, already an amplifier in the LNBF. I don't think an additional amplifier would help unless the cable run from the dish to your receiver is very long.

 

[cyberham]

I happen to have a satellite splitter/combiner handy. Electronically, if I installed it, without using a diseqc switch, between 1 receiver and the LNB on each different dish, nothing would be damaged I assume. The splitter/combiner has power pass on each port.

Worst case, the signal would be worse if combining was out of phase. My guess is phasing would change and the signal might be erratic. But it's easy to try once I have a second dish installed.

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[Titanium]

Might have better luck with the project if using PLL LNBs referenced to a single external generator.

 

[cyberham]

I have one PLL LNB which I'm using now. My other spare LNBs are not PLL (GeosatPRO bullets, etc.).

External generator.......hmm.

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[harshness]

The dish is right at ground level now mounted on a wooden pallet.

Before this happens again, I'd suggest a more solid mount.

Next is to invert the dish so I can continue the journey westward along the arc en route to the real target of 125W. KBS on 123W should be easy then it's just a bump west to PBS through the trees and at 11 degrees elevation.

While allowing you to point at the appropriate slot, consider how much atmosphere the signals are having to pass through to get to you.

 

[cyberham]

The pallets are solid and I won't have dishes falling to the ground anymore since they're on the ground. My property is extremely unfriendly to satellite signals since I am surrounded by trees. The moveable pallets will allow me to peak through the trees at the satellite I wish. Fixed dishes are much simpler than a motor in this situation.

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[cyberham]

I've had good luck with inverted dishes to get 15W previously in years past. 15W is at 20 degrees elevation for me. With a 22 degree offset dish, that means pointing it into the ground. So inverted was the solution. 103W is about as far west as I can go without inverting the dish since it is 25 degrees elevation.

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[a33]

Next is to invert the dish so I can continue the journey westward along the arc en route to the real target of 125W. KBS on 123W should be easy then it's just a bump west to PBS through the trees and at 11 degrees elevation.

I always understood that an inverted dish receives more ground noise than a normally mounted offset dish, as the LNB is pointed downward, and receives the ground noise as 'spill-over' at the edges of the dish.
However, I very much like the creativity behind the 'non-conventional' inverted setup.

An offset dish of which the dish face is looking down, is still looking up IMHO, when the 'boresight' of the dish is aimed at the satellite above the horizon. The noise from the ground is never mirrored to a single focal point.

BTW. The best 'amplifier', of course, is a (bigger) paraboloid dish.

Greetz,
A33