Skewing the Geosat Pro CK1 LNBF

[linuxman]

Ok, I have a question about skewing the Geosat Pro CK1 LNBF.

The problem:
I have the CK1 arrow indicator currently set at precisely 9:00 as per the instructions that were given to me.

On G11, the vertical channel that reads "due to blackouts", will not lock and display on either the Traxis 3500 or my "new"/used Coolsat 5000 that I just got. (I got it for a reason. I haven't really ever gotten used to them, but it does what the Traxis won't do.)

The same is true on AMC6 NASA vertical channels.

The Coolsat will lock it a little longer, and actually display the picture for a second or two, then goes completely out on both satellites.

The reading when locked on both the Traxis and the Coolsat is about 75% SQ. Both should lock and display the channels.

All lock and display fine on the Pansat, and it shows about 75% SQ. All lock and display fine in MT using the Twinhan card.

BTW, all Ku Vertical channels display fine.

The Question:
Could this mean that the skew needs to be adjusted slightly in one direction or the other on the CK1?

If so, which direction would you experts move it?

I would assume the same would apply to the BSC-621 too.

 

[voomvoom]

Try it one way and if it don't work try it the other way.

 

[gabshere]

well you know my bsc621 is pointed more toward 6 on the clock

AMC6 NASA vertical channels

my nasa vertical channels ar at 97% signal and 87% Quality on my coolsat 5k

was the coolsat new what version sw is on it ?

 

[linuxman]

Try it one way and if it don't work try it the other way.

Thanks Al.

I was hoping for a logical direction to move it since the verticals are the up and down signals, and the horizontals are the side to side signals.

Perhaps, when I tweak it on Saturday, the problem will resolve itself.

Verticals on the West side seem to be fine with that amount of SQ.

 

[linuxman]

my nasa vertical channels ar at 97% signal and 87% Quality on my coolsat 5k

I agree, the C-Band side still needs to be a little higher.

Again, I'm hoping for the tweak Saturday to help correct some of that.

 

[linuxman]

I have been thinking about the question, and have done some thinking.

I have a theory about what is happening on my skew. I hope the drawing helps us all to understand what we are trying to achieve in tuning our dishes. I am not the best draftsman in the world, so keep that in mind when viewing my drawing.

First remember, that the Birdview dish has almost perfect surface accuracy, and it's parabolic form is nearly perfect too. It is also a very flat dish, .41 - .42 F/D ratio.

The factory Focal Length as measured by me from the center of the dish to the mouth of the OEM feed-horn was 39-1/4". I now have the Focal Length set to about 40-1/4". Using 6'5" as the viewable area on this 6.5' dish, the calculated Focal Length is 41.1". If you use the entire 6'6", the calculated Focal Length is 41.9". For now, let's go with the 41.1" Focal Length.

Keep in mind that this dish was designed for C-Band at the time it was made, so in my opinion they set the FL shorter to avoid side-lobe interference. Remember the time I thought I had a signal on G27 C-Band with the Perfed dish? It turned out to be the signal from G13 bleeding over. It was as nearly as strong as the signal on G13 itself. That's the problem you run into with these super gain flat dishes.

So my theory is that not having the dish centered on the arc properly coupled with the fact that I have increased the distance from the LNBF to the dish, I still have very strong C-Band signals, but the Verticals are being cheated so to speak. Especially on the Center and Eastern side of the arc. I have good lockable SQ on NASA at 137W, and the verticals on G15 are nice and strong and lockable, but there, the Horizontals are a little weak.

The Ku would still be quite strong because of the accuracy of the dish. Here is the drawing to illustrate my point. I left some of the circles blank for further illustration, or for another draftsman to pick it up and add to it.



I may be completely wrong, and if so, please correct me. I know if Mike Kohl sees this and I am wrong, he will jump in to bring me back to reality. He has done it before in phone conversations.

So jump in here and write some thoughts.

 

[mikekohl]

The focal length is in one place. If your antenna has a stated diameter and
f/d ratio, the focal length is a simple mathematical calculation that should work every time. While there may be some adjustments, such as maybe 1/4 inch allowance for a center plate on some antennas, if the antenna is properly assembled and performing correctly, the focal point or hot spot of your signals should be identical.

Many feedhorns and LNBFs are designed with the C and Ku-band probes in different locations, separated perhaps by 1/4 or 1/2 inch. You must generally compromise for the best signal on Ku-band (since its hot spot is a circle about 1/3 the diameter of the C-band hot spot), and let the C-band performance fall wherever it does. In the real world this compromise usually works, with further in and out fine tuning possible after you have become familiar with any peculiarities of that particular feedhorn or LNBF, as compared to other models.
Polarity peaking is a clockwise or counter-clockwise adjustment, and on a fixed dish (not a polar mount), you must tweak it away from center position when you are anywhere besides perfectly aligned with due south. You're either in the right place, or not at all, and the perfect window can be a sweet spot as small as 2 or 3 degrees in rotation. Keep tuning if you're not there!

 

[Corrado]

Linuxman, my BSC621 works perfectly on my setup with the index in the 6 o'clock position for C band. It will perform until the 7 o'clock on Ku. The F/D seems to be with the edge of the feed 1" out of the scaler ring on my 10' Unimesh. I honestly never checked what the specs should be, but it works great right there.

 

[linuxman]

From Mike Kohl:

The focal length is in one place.

I am assuming that you would suggest using the 8'6" diameter as measured since there aren't any stated specs.

If your antenna has a stated diameter and f/d ratio, the focal length is a simple mathematical calculation that should work every time.

That being the case, I need to move the scalar out another 1-3/4 inches.

Many feedhorns and LNBFs are designed with the C and Ku-band probes in different locations, separated perhaps by 1/4 or 1/2 inch. You must generally compromise for the best signal on Ku-band (since its hot spot is a circle about 1/3 the diameter of the C-band hot spot), and let the C-band performance fall wherever it does.

I understand there is a compromise between the two signals.

Polarity peaking is a clockwise or counter-clockwise adjustment, and on a fixed dish (not a polar mount), you must tweak it away from center position when you are anywhere besides perfectly aligned with due south. You're either in the right place, or not at all, and the perfect window can be a sweet spot as small as 2 or 3 degrees in rotation. Keep tuning if you're not there!

Will do as soon as I move the Focal Length to where it should be.

Thanks Mike as always for your input.

From Corrado:

my BSC621 works perfectly on my setup with the index in the 6 o'clock position for C band. It will perform until the 7 o'clock on Ku. The F/D seems to be with the edge of the feed 1" out of the scaler ring on my 10' Unimesh. I honestly never checked what the specs should be, but it works great right there.

Hey Corrado.

The BSC-621 has a different setting than the CK1. As per the instructions from SatAV, the arrow on the CK1 is to be pointed at 9:00 and adjust from there.

Both of these voltage controlled LNBFs appear to be difficult to tune in as compared to standard Co-Rotors. I think the reason is the different position depth of the probes vs. the Co-Rotors.

Even though they may differ, one should be able to find the right spot for the compromise of C and Ku.

That's what I am trying to achieve. I am just old, slow, cautious, and a perfectionist.

I'll get there, it may just take a while. It is as important for me to understand the theory as it is to get the actual experience.

Some day if I can ever afford it, I'll buy a professional signal meter which would help a lot.

 

[linuxman]

The temp actually warmed up considerably about 4:00 PM yesterday and I managed to do some minor adjustments on polarity doing just as Mike Kohl suggested, simply turning clock-wise and counter-clock-wise on the LNBF.

All to no avail. Still could not get the C-Band Verticals to lock on the Traxis or Coolsat. Oh and BTW, I checked all the way across the arc, and no C-Band Verticals. When it does lock for short time periods, the signal is 75% or higher, but it won't hold. Works fine with the Twinhan and Pansat, just not the Traxis or Coolsat. Go figure.

This morning I am going to move back to the OEM position of the scalar and center the dish on the arc, and adjust elevation tweak for Ku signal. That is where I had the best C-Band. There has to be a reason the manufacturer set the stationary Focal Distance at that point. The CK1 worked fine with both C and Ku on the Perfed dish using that position and I think this one will to once I tweak everything. If I have to, I'll switch the dishes and put the Perfed one back on this mount and the solid on the other.

In the worst case scenario, I will buy an ADL 2+2 feed-horn with powered multi-switch as Mike suggested, but I will make this work for the setup I want.

I took a couple of pictures of the throat of the CK1 so everyone can see the inside of it.

 

[truckracer]

Interesting that the CK-1 lnbf does not have an isolation bar for C-band. Just the c-band probes then the internal ku scalar ring. Ku part has an isolation bar. Hmmmmm.

That must be the design difference. I gave up on my BSC-621. Too much of a compromise for me to live with. (I know this is a ck-1 thread) but still related.

 

[linuxman]

I know this is a ck-1 thread) but still related.

Course it's related. I should have named it "Skewing a voltage controlled LNBF", but didn't think about it when I started it.

BTW, if you want to get rid of that BSC-621 real cheap, I might be interested. I would like to see for myself the difference not only in design, but in performance.

 

[linuxman]

Made some good progress this morning.

I decided not to change the Focal Distance as previously planned, instead I peaked the dish for elevation on G11 and gained another 15% SQ on Ku according to the Pansat meter.

Gained another 5% SQ on C-Band G11.

Swung it over and got White Springs for the first time since the digital level adjustment to the elevation/declination I did a week ago.

Tried centering on the arc to get White Springs a little better and discovered that I was on the center. There is no pushing down or pulling up on Birdviews. If you put enough pressure either direction you go from what you have to zero. I think it would hold 50 lbs. of weight on the edge before losing signal.

This afternoon I am going to work with the Focal Distance some more. I might even do as planned earlier now that the dish is peaked for elevation and see what that does for me.

 

[truckracer]

My sami dish 10' is flimsy. I believe you could break it pushing too hard up and down.
I have heard those birdview's are tanks. Very strong and durable.

The 6' prodelin I had was super rigid and strong.

My 7.5' sami mesh is solid as a rock. They should have made the ribs a little bigger that 1"x1" on the 10' version.

 

[linuxman]

Yes I have a 10' SAMI dish running the family 4DTV, and was never impressed with it. It works, but nothing outstanding.

Made it back to the roof this afternoon after lunch and a phone chat with Anole. I tried an experiment just to see what would happen. I drilled and tapped two holes for the set screws near the back side of the scalar and pulled the feed-horn back into the scalar 3/4". No difference in signal on Ku or C-Band.

I then took the couplers off and put everything back to the factory Focal Length to see if the far recessed feed-horn had any difference there. None.

Put the couplers back on and added a nut, so I am now at 40-1/2" to the lip of the feed-horn. I would have just taken it on out to the prescribed 41.9" that is calculated, but will need to go by Lowes tomorrow and pick up some more couplers.

The signal has come up on the C-Band side a little, so I am headed in the right direction. When the C-Band and Ku signals are equally high or when I reach 41.9", I'll quit whichever comes first.

I am no longer using the arrow on the feed-horn at 9:00. I am looking into the throat and lining up the vertical probe with the vertical position on the dish. In other words vertical probe at 6:00 position.

The traxis still won't lock the vertical signals for more than a couple of seconds. The Coolsat now locks some of them for 5 seconds or so, loses and then comes back in.

We're not talking low signals here. 82 SQ on the Coolsat, and 75 SQ on the Traxis. Both are high enough for lock on those machines.

I don't know where to put the vertical probe to get the verticals to lock on those machines?

Again the Pansat, and the Twinhan are having no problems locking and displaying the signals.

Just to let everyone know where I am on signal, G3 Equity 7/8 FEC are at 80% SQ on the Pansat meter and playing fine without flickering.

Any suggestions on getting the verticals to lock on the Traxis?

 

[gabshere]

well i've been working and modifing my BSC621 as Truckracer noticed the isolation bar for our bsc621 c-band part covers the ku probe in the area that should be the focal point for ku. so i removed that bar. but when i went to the tech bulliten on the BSC621 to make sure my alignment was correct. it shows the ku probes just the opposite from the CK-1 so maybe the is why your having trouble with several receivers ?

just a thought

 

[linuxman]

but when i went to the tech bulliten on the BSC621 to make sure my alignment was correct. it shows the ku probes just the opposite from the CK-1 so maybe the is why your having trouble with several receivers ?

I rotated the image so that the probes match and after doing that, they look like they are both aligned the same.

See the picture.



EDIT: Where does the external arrow line up with the probes on the BSC-621?

I would suspect they are both lining up the exact same way. They are just using two different locations for the arrows on the outside.

 

[gabshere]

well i was looking for a clear picture, i could olny see one ku probe good

 

[truckracer]

Mine was weird(BSC-621). I could cover the internal scalar with foil duct tape and trim it off with an exacto knife around the edges and cut out the center hole, re-assemble it and it would improve some ku signals while killing off others.

I then skewed the unit to peak C-band on G10R getting both polarities to come in as equal as I could get them.

Ku was totally dead at this point on G10R. I then left the lnbf on the dish and removed the three screws holding the KU section and give the ku part a little twist in the housing. held the ku part up aligning the screws and boom KU came in. G10 R ku came in at 84% on the Pansat 9200HD.


Only problem was KU was always hit and miss. Take for instance on AMC-3KU, I would get 38-55% bouncing around on PBS KU. The patient channel would be pegged at 99%

One of my buddies with a 75 cm offset dish gets 78% - 90% across the board on AMC-3!!


I just could not get this lnbf (BSC-621) to perform consistent across the arc. I had it at one point where I could not get verticals. Horizontals booming in pegging the meter on c-band.

When I got the Verticals to come in, Horizontals took a big hit.

Seems this design has a lot of cross pol interference. Needs more isolation internally.
My old astrotel c-band lnbf I am using now has a metal wedge in the bottom instead of a round rod to isolate polarities.

My HBO and Max's on G1 are booming in.


On G25Ku some tp's would come in and some wouldn't lock.
The ones that came in came in pretty good and the others were at 10% quality.

I have set up a few big dishes for ku - this 621 got the best of me.

At one point I had the 621 to the point that on ku I would do a blind scan on SBS-6 and ONN would scan in as both horizontal and Vertical with good signal on both polarities.

 

[linuxman]

Worked on the skew and Focal Distance all afternoon yesterday. Finally go the Traxis to lock and display the Vertical C-Band signals.

I made the decision using Mike Kohl's assumption that there is only one calculated Focal Distance for a dish and moved the scaler/feed-horn to 41.9 inches to start with.

It was a long way in to where the numbers are best for both C and Ku. I ended up at 40-7/8" for the final Focal Distance. I was at 40-1/2" when I left it Saturday.

Here are the numbers from previous Perfed dish with Pansat and Co-Rotor and the Traxis/Geosat Pro combo. The 1st reading is the Pansat/co-rotor, 2nd is the Traxis/Geosat, the third and fourth readings are the Pansat/Geo/Solid BV, and the Traxis/Geo/Solid BV combo.


-----------------------Pansat/Co-rotor/Perfed--Traxis/Perfed--Pansat/Geo/Solid--Traxis/Geo/Solid
AMC7 - 137W 4060 V C-Band-----NA SQ---------NA SQ-----------45% SQ------------65% SQ
G15 - 133W 3745 H C-Band------72% SQ--------68% SQ----------15% SQ------------30% SQ
G27 - 129W 11964 H Ku----------72% SQ--------68% SQ----------63% SQ------------wouldn't ?
G10 - 123W 11718 V Ku----------75% SQ--------73% SQ----------75% SQ------------73% SQ
G3 - 95W 4039 H C-Band Equity-NA--------------NA-----------------60% SQ------------65% SQ
G11 - 91W 3720 H C-Band-------78% SQ--------78% SQ----------90% SQ------------77% SQ
G11 - 91W 3858 V C-Band-------NA% SQ--------NA% SQ----------75% SQ------------73% SQ
G11 - 91W 12062 V Ku-----------60 - 65% SQ---58 - 61 SQ-------75% SQ------------72% SQ
AMC3 - 87W 12144 H Ku---------70% SQ--------55% SQ-----------75% SQ------------64% SQ
AMC2/16 - 85W 12195 H Ku-----80% SQ--------70% SQ-----------90% SQ------------77% SQ
G17 - 74W 11734 H Ku-----------80% SQ--------75% SQ-----------90% SQ------------74% SQ
AMC6 - 72W 12053 V Ku---------72% SQ--------72% SQ-----------99% SQ------------78% SQ
AMC6 - 72W 4043 V C-Band-----77% Sq--------75% SQ-----------60% SQ------------72% SQ
IS9 - 58W 4040 H C-Band-------75% SQ--------81% SQ-----------90% SQ------------77% SQ
IS3 - 43W 12048 H Ku-----------NA---------------NA------------------75% SQ------------74% SQ
Hisp - 30W 11883 V Ku----------NA---------------NA------------------75% SQ------------75% SQ
Hisp - 30W 12171 H Ku----------NA---------------NA------------------90% SQ------------76% SQ

The Ku numbers across the arc are excellent.

The C-Band are still lacking somewhat. I can get 90% SQ on G11 H and 75% SQ on the vertical side as you can see.

I saw as high as 90% SQ on G10 11720 V, but that is down because of skewing for better H signals.

I refuse to believe that I can get the 90% C-Band on G11 and not get better C-Band signals across the arc.

Maybe something shifted on the mount and plumb is a little off, or something. I will check that today.

Look the numbers over and see if they tell me anything that needs to be done.

Any suggestions?