Ku Skew

[dunnsept]

I'm trying to get some Ku FTA stuff going. I hooked up a Norsat 4508A today.
So, here's my question:
on a given sat, will the Ku band skew match that of C-band?

ie: I am currently on G18. On C-band, my V skew is around -20 and H is 60 for the highest quality.
On the pansat Ku, I get ZERO quality. Should I start with setting skew to -20 and then try bumping the dish around or do I have to start from ground zero and do both skew and dish?

thanks!
Paul...

 

[Lak7]

Skew should match, pretty close at least.

Have the correct LNB settings in the Pansat?

 

[Mr Tony]

the only sat in the main arc (main arc being 72-137) that KU is off is AMC1
C-Band is normal
KU Is off by like 25 degrees OPPOSITE the way it should be...Basically the skew for AMC1 KU is about the same as Horizon 2 (74W)

 

[dunnsept]

OK.. thanks.. somethings not right then.. I was getting quality of about 15% on G18 with skew set to 30 (on c-band it's normally -20)
what should I use for the settings for the LNB? It's a pansat 2500a and I'm set to:
standard
10750
22khz: off
diseqc: off
positioner: disable (moving the dish with the 4dtv now)

 

[Lak7]

You could need to be better aligned.
For Ku on a BUD, alignment must be perfect.

 

[equant]

You could need to be better aligned.
For Ku on a BUD, alignment must be perfect.

I don't understand why this is, but I know from experience it's not easy to get Ku on a BUD. I can get Cband transponders on the whole arc, but I can only get channels on one Ku transponder on 97W. Nothing else!

 

[guapoharry]

What kind of BUD?

 

[Anole]

You could need to be better aligned.
For Ku on a BUD, alignment must be perfect.

Yea, what he said.
There are two possibilities, and I'll wager both apply:

- the positioner moves the dish close enough for C-band, but not Ku
it may not even have the resolution to land on a Ku bird
for example, old Birdview dishes were upgraded to an 8-magnet wheel and did dandy on C-band
but the current 24-magnet sensor wheel is necessary for proper Ku alignment.

- oh, you have a Norsat and a corotor? Okay never mind on that suggestion.
I was going to say that the Ku tuning is very delicate on the LNBFs, but it still is to some extent with a corotor.

 

[turbosat]

I don't understand why this is, but I know from experience it's not easy to get Ku on a BUD.

Bigger dishes 'see' more precisely than smaller ones, so your tracking has to be much better. No slack in your pivot points, polar mount cap or actuator attachment points. Declination has to be spot-on, and the is the place where you find if your pole is 'plumb' enough too! I think a lot of the older buds weren't really that great for ku, as most of what they were sold for was on c-band at the time. Other things that affect ku would be focal distance, and feedhorn centering.

 

[DishDigger]

I don't understand why this is, but I know from experience it's not easy to get Ku on a BUD.

I'd like to take a stab at an explanation. Though it may be wrong & difficult to explain, here's an attempt:

If the focal distance is short, as with a small dish, the LNB is close to the dish. A small off-alignment will still allow some of the signal to hit the antenna (inside the LNB). With a longer distance from the dish, as with a BUD, a small angle of off-alignment will completely miss the LNB. Try this, draw two lines from ONE point on a piece of paper. Have the lines spread just a little (shallow angle). Now, look at how far they are apart, say 1 inch from the point. Now look how far they are apart at three inches from the point. Consider the point as being where the signal leaves the dish and the 1" and 3" distances as being the location of the LNB's. The angle represents the difference in reflection of the signal when the dish is off-alignment as compared to being on-alignment.

Hope this helps, or makes sense.........

 

[dunnsept]

thanks guys.. I know there is some slop in that dish. I moved the dish back n forth pretty slowly to see what I could get, but wasn't sure where to start with skew.
I think it might be alignment. I would "bump" the dish a little and on the pansat, the quality would peak, then bounce up n down, kinda like I had bumped through the best focus point.
SWMBO is gonna be _really_ happy with me if I tell her that I have to put up a new dish (NOT!)

as I keep poking around at this Ku stuff on my dish (btw, it's a 9 footer, dont know brand)
what sat would you recommend to use?

 

[dunnsept]

well, I've got G10R right now. quality isn't great. bouncing around between 15 and 30 %, but at least I've got _something_ working.
I think that you guys might be right. when I try to "bump" the dish a little to tune it better, I totally lose the signal.. may also be the slop in the mount.. who knows.. but at least I've got some channels on there now

 

[mbarnes]

Back when I was in the business, we specified a minimum 2.4m dish for our Ku downlink users. I had 15 locations to maintain, each having one or two dishes, with 8 or so at the headquarters. All were 2.4m or larger and did Ku just fine.

Regarding Ku on a BUD. First, it should be a Ku rated dish. Due to the much shorter wavelength, the dish surface is much more critical. Mesh dishes are usually a waste of time. Dish alignment is much more critical on a larger dish as the dish has a much tighter focus or beamwidth. Remember rain-fade? That is because a typical raindrop is roughly the same wavelength as a Ku signal, so the raindrops absorb the signal. Compare the holes in a mesh dish to the size of a raindrop.

Regarding skew. Skew, like focal length and most other measurements related to dish alignment, is a geometrical function. Geometry is frequency independent. Since you are only dealing with relative angles, the frequency is immaterial. Therefore, assuming the satellite transmit antennas are properly oriented, the skew should be the same whether C, Ku, Ka, S, L or any other band you want to play with.

 

[14karat]

Generally you peak for C first, then peak for Ku - which will typically improve C even more.
Unless you are using one of the 'off-caliber' 621s like I have...

The focal point on my 10' was probably the most touchy point for Ku. Once I got it right, the dish can bounce around quite a bit in the wind and the signal will hold (to an extent, of course)

 

[dunnsept]

I got G10R pretty good now. It is a 9' mesh dish, but the holes are fairly small. doesn't really matter right now as it's all that i have to work with. the other dish I have is the Perfect 10 7.5' which is in pieces in the barn.
I turned it on today to see if it was still at least semi-dialed in. and the kids and I watched Jack Hanna for a while.. nice picture too .. only once every 10 mins or so was there a "blip" on the screen. I'll play around with it more later on.. and once I find some cool channels, I can work on convincing SWMBO that I need to put up another couple dishes in the spring

 

[Lak7]

If there is "any" windy, don't bother tweaking.
Check all bolts, make sure everything is tight.
I had to replace my Actuator 'cause the connection ball joints were rusted and loose.
I used Galaxy 28 (mt South Sat) and Galaxy 27 to tweak my the Elevation and Deinclination.

 

[B.J.]

In my opinion, one of the main reasons for Ku problems when C-band is working, is that the feed isn't at the focal point. I try to find a sat with C-band, and then while looking for signal on Ku, move the feed closer and further from the dish. This is particularly the likely explanation if you find that C-band is found at a different point than Ku is found

Also, if the dish is very old, like 25 years old, size of the mesh is less of a problem than the poor shape of the dish. A dish can work very well on C-band but not be shaped accurately enough to receive Ku, and very old dishes weren't designed with Ku in mind. If that's the case there isn't much you can do, although I used to have a dish that had cables and turnbuckles that would allow you to adjust the shape of the dish, but I never figured out a reasonable way of doing that.

 

[dunnsept]

I was in the barn looking for more "stuff" and took a look at the perfect 10. That has a really fine mesh, anybody have experience with Ku on the perfect 10s?
There's no way I can get that one in place for a few more months, more so with the cold spell that's on its way, or for Ku would I be better off going with a smaller solid dish?
also, what's another Ku sat I can use for more "testing"with what I have (that has some interesting channels on it AND reasonably strong transmitter)?
of course, now that I say that, in going thru what's on G10R, it's only the "E/I" channels that are so weak, there are some encrypted ones that go up into the high 50's for quality

 

[Lak7]

PBS stuff on AMC21 @ 125 west

If someone in the house can watch the Q Meter, try Pushing / Pulling on the Dish to see if anything improves.
Maybe just a small Elevation adjustment is necessary.

 

[dunnsept]

PBS stuff on AMC21 @ 125 west

If someone in the house can watch the Q Meter, try Pushing / Pulling on the Dish to see if anything improves.
Maybe just a small Elevation adjustment is necessary.

good suggestion.. thanks.. I had thought about that a while ago, but then forgot. ;-( (I suffer from CRS)