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Captain_Kurtz

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Reply with quote  #31 
Quote:
So the first step for me is to get an angle finder/inclinometer, yes?


If you're already tracking the arc except at the east end, then there's no need to spend money on one if you don't already have one.
You should be able to fine tune the tracking using signal strength alone from there.

As for the combo C/Ku LNBFs, I'm not a big fan. Maybe it's just the models that I tried, but I tried several.
I was trying to find a good match for a 5.5' mesh dish, and on a 6' solid metal dish, where every ounce of dB of C/N matters.
None of the C/Ku LNBFs gave results that were as good as using an "older style" C-band only LNBF, by a significant margin.
By "older style", I am referring to the ones made from much heavier metal than the newer ones. Made in the 90s IIRC.
I don't believe the metal itself accounts for the difference in performance - my theory is that the older ones have circuits made entirely from discrete components that noticeably outperform the newer ones which I believe rely more on IC chips (plus a handful of discrete support components) and a "PLL" clock circuit.
The ones that I have (they are occasionally for sale as on ebay)  that work really well are labeled "Zwave", "Diamond", and the other one has the label worn off, but I believe it's an old Chaparral.
My preferred solution is to use an orthomode C-band-only feedhorn on a large dish, and a separate Ku-only dish on a diseqc motor.
No matter how well engineered and built, a combo C/Ku feedhorn is a tradeoff that will cost you some performance.
Of course if a combo C/Ku LNBF gets you all the channels that you want, then that's great. YMMV.


jdcpa

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Reply with quote  #32 
Quote:
Originally Posted by Captain_Kurtz
Thanks Jim - that's exactly the page that I was looking for.
Only available on web archive now?
That page's tuning dish to satellite arc chart is apparently derived from the Baylin and Gale books from the 1980s, page 199 in "The Home Satellite TV Installation & Troubleshooting Manual", and page 212 in "Ku-Band Satellite TV: Theory, Installation and Repair". Other images on that page seem similarly familiar.

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Hurricanes Hermine and Irma 28N paths. C Norsats: 8115 on Corotor II on 10' mesh; 5215G5 X2 on Bullseye I on 12' mesh.
a33

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Reply with quote  #33 
Quote:
Originally Posted by Pops
So the first step for me is to get an angle finder/inclinometer, yes? 


If you have a smartphone: there are plenty of apps that have an inclinometer! Quite easy to use...

Greetz,
A33
Pops

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Reply with quote  #34 
Hmmm . . .  thanks for the idea.  
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"My neighbors to the east cut down their weeping willow and now there's barely anything to watch between 85° and 72° !"
rikoski

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Reply with quote  #35 
All of this assumes that your post is vertical to a small fraction of a degree.

a33

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Reply with quote  #36 
Quote:
Originally Posted by rikoski
All of this assumes that your post is vertical to a small fraction of a degree.

(in the east-west direction!
North/south angle deviation can be corrected with the axis elevation.)
Captain_Kurtz

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Reply with quote  #37 
It also assumes that the pole is rigid enough to support the weight of the dish without significant deflection at the ends of the arc.
A pole that's not perfectly plumb - in any direction - can be compensated for by adjusting the tracking parameters (azimuth, elevation, and declination) using signal strength as your guide. A pole that deflects enough to noticeably affect tracking at the ends can be a nightmare, and your best choice is to stiffen (e.g., fill with cement) and/or brace it.
BTW, also keep in mind that the design of the polar mount is itself a compromise, so no matter how well it's adjusted, it still won't "perfectly" track the arc; the goal is to get it to track well enough within the limits of the beamwidth of your dish, which is a function of the size of the dish. The larger the dish, the higher the gain but also the more noticeable the tracking errors become because of the tighter focus (lower beamwidth).
It's not a bad idea to initially set the declination as accurately as possible to get the dish tracking the arc quickly, but don't be afraid to tweak the declination setting to get the best performance across the arc.
a33

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Reply with quote  #38 
Quote:
Originally Posted by Captain_Kurtz
A pole that's not perfectly plumb - in any direction - can be compensated for by adjusting the tracking parameters (azimuth, elevation, and declination)

If it is not plumb east/west with a motor setup, I don't see any way to really compensate and fully tracking the arc again. Of course you can find some compromise, but a real compensation it is not.


Quote:
Originally Posted by Captain_Kurtz
BTW, also keep in mind that the design of the polar mount is itself a compromise, so no matter how well it's adjusted, it still won't "perfectly" track the arc

I believe the 'modified motor angles' give a pretty perfect tracking of the arc, assuming the satellites really are at exactly the same distance from the center of the earth, and exactly above equator. Though I must confess I haven't done the mathematical checking on that, yet.
And I'm not sure about deflection of satellite signals just above the horizon ~ didn't read the basics about that, how that affects 'following the arc'.
Apart from that, I believe the 'modified motor angles' are 'perfect'.

Did you use the modified motor angles? Did you have to further calibrate your motor setup, after that?

greetz,
A33
Pops

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Reply with quote  #39 
Captain K, I sent you an e-mail.  

BTW, I do believe my pole is plumb.  Checked it again recently with a level and it looks pretty good.  

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"My neighbors to the east cut down their weeping willow and now there's barely anything to watch between 85° and 72° !"
Captain_Kurtz

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Reply with quote  #40 
Hello Pops -
Yes, got your email, and happy to help, but also cautious about opening a can of worms.
If it's cold where you are and your dish is tracking most of the arc well then I would leave it alone until the weather warms up.
The general procedure is to go to your southernmost satellite (not 103W, since you are in WA, correct?) and peak the signal there first.
I would only touch the elevation (at first) to peak the signal, then go to the east and west ends of the arcs to check the results,
by gently raising/lowering the dish to see which (if either) causes the signal to improve.
Then, consult the diagrams to figure out what among azimuth/elevation/declination needs to be adjusted, being careful to mark your starting positions for each, remembering what you last adjusted, and only adjust declination last and in small increments.
Keep in mind that as you are making the adjustments, you will probably have to tweak the stored positions of the satellites in your receiver.
And, being on the west coast, with your westernmost satellite high in the sky and much closer to the top of the arc than the west end of the arc, it will be difficult and confusing to distinguish between the case where you need to adjust declination and where you need to adjust azimuth.
Always go with azimuth first, and if that doesn't work then try a small adjustment to declination.
Finally, only adjust elevation and declination while on your southernmost satellite.
(If you have to make a small adjustment to declination, do it on your southernmost satellite, and also adjust the elevation in the opposite direction to compensate, to keep the signal peaked.)
I hope I explained that well enough that by studying those archived pages and charts that it will all make sense. [smile]

Captain_Kurtz

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Reply with quote  #41 
Quote:
If it is not plumb east/west with a motor setup, I don't see any way to really compensate and fully tracking the arc again. Of course you can find some compromise, but a real compensation it is not.


A pole out of plumb a few degrees east or west can be compensated for, and yes it's a compromise because the polar mount is itself a compromise - there is no absolutely perfect, just good enough within the beamwidth of your dish.

Quote:
I believe the 'modified motor angles' are 'perfect'.


"Perfect" within the limits of the resolving power (beamwidth) of your average FTA dish? Probably so, but not perfect in any absolute sense.

I refer you, for example to this excellent discussion about the inherent limitations of the implementation of USALS, which has several references and discussions about the inaccuracy and compromise in a polar mount, and how the choice of declination angle affects how the tracked arc interpolates the actual arc, (and in which you took part):

https://www.satelliteguys.us/xen/threads/usals-notebook.166471/

(My understanding is that the arc that a polar mount tracks tends to be too flat at the top compared to the actual arc, and not flat enough at the ends. Or is it the other way around? Or does it depend on choice of declination angle?)

Quote:
Did you use the modified motor angles? Did you have to further calibrate your motor setup, after that?


Full disclosure, for my 1m metal Ku dish on a diseqc motor (a Stab HH120), I didn't use or measure any angles. I gave up trying to find flat surfaces to measure, and I didn't have an accurate inclinometer at the time, and I was too impatient, and I have a really good spectrum analyzer and signal meter anyway, so I just eye-balled it on my southernmost satellite, and away I went, using the charts to adjust everything until I was tracking perfectly from Hispasat at 30W to Horizons 1 at 127W. It took a lot fewer iterations of adjustments than you might suppose to get it perfect without obsessing about measuring and setting all the angles first, only 3 or 4 times across the arc, IIRC.

And that is my point. It's not to be pedantic about whether or not the polar mount absolutely perfectly tracks the arc (it doesn't) as opposed to good enough within your dish's ability to notice a difference, it's to point out that setting the initial angles isn't all that critical if you follow the procedure correctly.
Sure, it will save you time and effort to set the angles as accurately as possible initially - but only up to the point that you aren't spending too much time on it. Within a degree or two for elevation and within a half degree or so for declination is more than good enough to get started IMO.

What I completely disagree with is the philosophy of "Only set the declination once, then never touch it again". I think that's a remnant of the days of analog, and most people having C-band only, and 8' dishes. It might have been good enough then, but today with DVB-S2 and 16ASPK and aggressive FEC rates like 9/10, you need every drop of CNR you can get. YMMV.


a33

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Reply with quote  #42 
Thanks for your detailed reaction.

Last night I did the mathematical checking if the 'modified angles' perfectly track the arc, and the answer is indeed NO, I noticed.
So I was wrong, in my assumption. [frown]

I had expected a perfect match, due to my somewhat limited understanding of cones, circles and ellipses. However I tested if the modified angles, when perfectly aligned to the due south and the opposite satellite, hit exactly the arc at plus or minus 90 rotating degrees from south, using the forward axis tilt of the modified angles (so that the 90 degrees rotation sees a greater part of the satellite arc, than the 90 degrees rotation with an axis parallel to the earth axis). In the USALS notebook thread, I never understood how they had tested that, because I don't understand vector mathematics. But I'll re-read that whole thread again, now!

My calculations indicate: At 90 degree rotation, the modified angle looks a little bit UNDER the clarke belt; with a maximum of a little under 0.04 degrees, at latitude about 35 degrees.
(I didn't check how that is at other rotation angles, as those calculations are much more difficult angles than at 90 degrees...)


Assuming my calculations are right, I will have a look again at the values of the normally used 'modified motor angles charts' (such as in the above mentioned link): if there could be a better compromise.
If I recall right, these charts are made on the same basis that I did my calculation on: perfectly aligned to the due south and to the opposite satellite.
If i find a 'better compromise', I will follow up on the Usals Notebook thread I guess.


If these compromises to the perfect motor setup are about hundredths of degrees, I don't follow your reasoning about east/west non-plumbness compromises though. They might be about much more than hundredths of degrees.


I'm not sure what originally was the reason for the 'leave the declination untouched' paradigma. You've got a point there!


Interesting, thought-challenging stuff!

Greetz,
A33
conway

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Posts: 250
Reply with quote  #43 
ok i purchased a Titanium Satellite C1 PLL Cband LNB. I'm going to use my 10 footer as a dedicated Cband Dish and get me a Dedicated KU band dish. I am curious on how much better my signal will be with the new LNB. That LNB gets really good reviews. 
Pops

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Reply with quote  #44 
Originally posted by: Pops
Quote:
Curious about something . . . 
I did not do the initial install of my 10-ft. mesh, but did do some elevation adjustments last summer on 103 west and went from about 75% quality on NBC feeds to 88%.  I was patting myself on the back until I realized recently that I lost a fair amount of signal at 78 west.  All other birds SEEM as good as ever.

In an effort to get more signal at 78 west, today I did a dish push pull test on 81 west (3850 mhz:  80% signal quality) and 72 west (11740 mhz and various others).  I wasn't able to get any more signal at either location. 

My Icecrypt will still blindscan in a handful of signals at 78 west, but they aren't strong enough to display any signal quality, which makes it tough to do the push-pull test there.  So I'm scratching my head once again because only 78 west is posing a problem for me.  Questions:
1) How is signal quality for others on 81 west 3850 mhz, and the signals on 72 west with 30000 symbol rate?  
2) Anyone notice if 78 west signal strength has weakened in recent months?

Thanks.

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"My neighbors to the east cut down their weeping willow and now there's barely anything to watch between 85° and 72° !"
a33

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Reply with quote  #45 
Quote:
Originally Posted by Captain_Kurtz
What I completely disagree with is the philosophy of "Only set the declination once, then never touch it again". I think that's a remnant of the days of analog, and most people having C-band only, and 8' dishes. It might have been good enough then, but today with DVB-S2 and 16ASPK and aggressive FEC rates like 9/10, you need every drop of CNR you can get. YMMV.


I looked into this a bit.
I think fine-adjustment on declination angle is very difficult.
The declination angle determines how well you track (the visible part of) the Clarke Belt.
When using the 0-180 degree calculation for modified declination, the declination is maximum 0.04 degrees off of the Clarke Belt (for a location at LAT 35); assuming you keep due south/north perfectly aligned.
When using the 0-90 degree calculation for modified declination, that could even be a little bit less.
So the fineadjustment should take place in a zone of maximum about 0.05 degrees, I guess; or your total deviation from the Clarke Belt will increase again.
So I would think the first step should be setting the (modified) declination angle as accurate as possible. The fineadjustment for the most difficult satellite can then be done with elevation adjustment.
This all, assuming that the feedhorn is at the right offset/prime focus location; if it is not, a 'declination correction' can be needed as adjustment for the incorrect offset angle.

NB. A difference of 0.04 degrees modified declination angle would mean, on a 2 meter dish, a displacement of =~ 0.7 millimeter of the dish edge.


One can reason exactly the other way round: set the rotation axis elevation very precise, and then fineadjust with declination.
If the elevation angle is set very exact, that would imply that the declination fineadjustment should be in a range of the above mentioned .05 degrees.
So in theory that would work also.
Also if you have two very difficult sats, you could try to find the elevation/declination combination that fits these two satellites perfectly, at the cost of suboptimal adjustment for the rest of the arc.
However if it is your aim to follow the whole visible part of the arc as optimal as you can, and when the elevation angle isn't set that accurately (at less than .05 degree precision), the risk is that you adjust the declination to a value that doesn't follow the rest of the arc very good.


So I can understand when people say: check that LNB is in the right offset/primefocus angle towards the dish, then set the modified declination angle very precise; and then (fine)adjust on axis elevation (if needed).


BTW (Background):
The Clarke Belt is of course a circle.
The projection of the elevation angle and declination angle of the motor setup on the plane of the Clarke Belt is not quite a circle, but slightly ellipical (that is, for locations not on the equator, up to LAT 81 degree).
This circle and ellips have a maximum of 4 crossing/touching points.
By adjusting elevation and declination angle, you try to have the crossing/touching points at or near the most difficult satellite positions, and inbetween the touching points to have a 'distance' between circle and ellips that isn't too big.


Greetz,
A33

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