Channel Master 1,2m issue

[polgyver]

Thanks for sharing those pictures. Construction looks sooo complicated. So, You've tried, and your conclusion is.....?
I am not sure I understand need for second laser. Could you explain process you went through?

Believed that a picture is worth a thousand words... now, it seems, a few words are still needed...
One laser projects a beam along the LNBF axis of symmetry. Not movable.
Second laser can display a cone, within which the LNBF "sees" the incoming radiation (reflected from the dish).
First laser reveals, that the LNBF is pointed BELOW the dish's centre (assuming, the four mounting screws define the centre ).
The second laser, sitting on a ball bearing, thus rotat-able, reveals a cone, which, surprisingly, has a "preference" for the upper side of the dish.
The cone angle was adjustable, so, I chose such an angle which was within the dish's face.
Referring to a clock's face, the laser shone at the edge at 12 o'clock.
9 o'clock and 3 o'clock - 2 " from the edge.
6 o'clock - laser was 3 1/2 " from the bottom.
So, LNBF is pointed BELOW the dish's centre, and, still, is illuminated by the upper part of the dish? Neglecting the bottom?
FaT Air is right, the manufacturers of the dishes prefer that the LNBF "sees" rather thermally cold sky than warm Earth (optimum performance).
Cheers, polgyver

 

[RimaNTSS]

BUT I don't think there will be much, if any, improvement in performance.

It is like in the room where one of 3 light-bulbs are not working, some can say, that there is enough light from 2 working bulbs and we will not see any difference

Do you guys seriously believe Channel Master would design their dish and feed system wrong, and it would stay that way for almost 20 years without anybody else saying there's a problem?

Maybe it is time to say so or, at least ask a question?

manufacturers of the dishes prefer that the LNBF "sees" rather thermally cold sky than warm Earth (optimum performance).

Why do not use then feeds with more narrow illumination angle and use whole surface of the dish?

And, we started to argue here about issue which is maybe issue of only mine antenna. Did somebody else checked their CM1,2m LNB's aiming point? Perhaps it is time to ask manufacturer?
Thank everybody for participation in discussion.

 

[RimaNTSS]

And, to add more fuel in the fire, there is picture of another 1,2m meter dish (made in West Germany), it has slightly different parameters than CM1,2m (offset angle, f/d ratio). So, LNB on this dish is also pointed to the very center of the dish. Accidentally or with intention like some of you saying... I do not know. But would like to find out the reason behind that. Would also be interesting to check LNB's aiming point on bigger branded offset antennas, like Channel Master, Prodelin.... etc.

 

[Radioguy41]

An offset feed dish is meant to be offset from prime focus by whatever degree the mfg documents in order to peak the signal. It is not meant to point directly at the satellite as a prime focus dish does. Maybe this image will help explain it better. Note the angle of the two different style dishes.

 

[RimaNTSS]

An offset feed dish is meant to be offset from prime focus by whatever degree the mfg documents in order to peak the signal. It is not meant to point directly at the satellite as a prime focus dish does. Maybe this image will help explain it better. Note the angle of the two different style dishes.

This explains very good difference between prime-focus and offset dishes. I think everybody knows very well how offset antenna is designed. But, unfortunately does not answer to question of LNB's aiming point. BTW, I wrote to CM manufacturer and asked my question to them.

 

[Radioguy41]

Actually the illustration does explain it if you study it. As the offset feed dish is tilted downward the sweet spot moves toward the center of the dish because the signal is reflecting at a different angle. Note in the illustartion of the offset feed the LNB is pointing at the center of the dish.

 

[RimaNTSS]

Note in the illustartion of the offset feed the LNB is pointing at the center of the dish.

That is useless illustration! Both antennas look like PFAs. Moreover, on the left picture LNB is certainly obstruct signal from satellite.
And on both pictures LNB is pointed to the very center of the dish.

 

[FaT Air]

Accidentally or with intention like some of you saying... I do not know. But would like to find out the reason behind that

If I was in your shoes, I'd be looking for a copy of Reference 6, that was posted, by me, in post #18

I'm absolutely positive the engineers that designed the dishes for CM, Prodelin, and others have read it and done their own 'nine yards' of testing to settle on their design. (the 'reason' is in ref #6, I bet)
Otherwise, I'm sure they would have done it, changed the 'aim point of the feed' themselves. And if their design wasn't 'as good as it gets' - CM wouldn't have been included the group of the most relied upon dish manufacturers to supply, worldwide, commercial and military needs.

Want to 'call and ask'? Here's the info I have on the Channel Master division:

Primestar / Channel Master dish info:

Channel Master dish division acquired by Andrew MFG.
Andrew MFG dish division split off and becomes ASC Signal in 2008.
ASC Signals (small dish 'division' I.E. offset) and Raven Antenna acquired by Satellite Holdings LLC.
(ASC Signal has retained the commercial BUD mfg)
Now rebranded as Skyware Global. http://www.skywareglobal.com/

Their distributor list: http://www.skywareglobal.com/index.php/distributors

Whoops, I guess you already did that

>>> I wrote to CM manufacturer and asked my question to them.

I hope you post their reply for all to read.
I also await for the results in any testing of your theory that you may do.

I would recommend just using it as designed. And strongly think you will appreciate the performance.
I'm sure it will outperform most, if not all, consumer dishes of equal size.

 

[RimaNTSS]

I hope you post their reply for all to read.
I also await for the results in any testing of your theory that you may do.

You bet! For tests, I think, it is better to use bigger antennas. On smaller ones difference cam be marginal. But, for sure, this summer I will do some tests using several 1,2m antennas and also some 1,8m ones (I have enough "Guinea pigs" to do tests).
But, till summer I should do more theoretical research, and this forum is one of the real sources. Thanks everyone for participation.

I'm sure it will outperform most, if not all, consumer dishes of equal size.

TBH, I do not believe 1,2m dish can outperform another 1,2m dish if they both are in perfect shape, LNB's phase center is co-located with antenna's focal point, LNB is pointing to the right spot, LNB's illumination angle is equal to antenna's openings angle. So, if everything is perfectly equal than the results will be equal .

 

[pacificrim]

It's usually a bit of adjustment no matter who made the dish. My guess is the elevation adjustment will fix the problem.

 

[Radioguy41]

That is useless illustration! Both antennas look like PFAs. Moreover, on the left picture LNB is certainly obstruct signal from satellite.
And on both pictures LNB is pointed to the very center of the dish.

Why is it useless, because you don't understand it or don't want to understand it? The LNB is obstructing the signal? Both LNB point at the center of the dish like they are supposed to. You don't seem to want to accept that it's correct so there's no point in continuing.

 

[RimaNTSS]

You don't seem to want to accept that it's correct so there's no point in continuing.

Main idea here is to get maximum out of antenna. But if you move feed out of antenna's focus you will never get maximum possible signal. That is why illustration is useless, for this topic at least.
To get maximum possible performance out of system, antenna should not be moved anywhere with LNB in focus.

 

[Titanium]

When testing the feedhorn aiming on a live satellite signal there are many possible sources of interence that might be eliminated by aiming at a different area of the reflector. This will of course, vary by frequency and satellite. Surface and pattern testing happens in an RF neutral facility with controlled single and multiple signal sources. I would suggest that the manufacturer correctly designed and manufactured the hardware to position and aim the feedhorn and included scalar to properly illuminate the reflector surface.

I don't have a model of that dish to check the feedhorn measurement or positioning, but the photos appear to accurately depict the feedhorn aiming that I have observed on these models during service calls.

Typically, commercial grade reflectors typically have a much more accurate surface than a consumer model. I agree that if all things were equal, the performance would be similar, but they are usually not equals...

 

[RimaNTSS]

Surface and pattern testing happens in an RF neutral facility with controlled single and multiple signal sources. I would suggest that the manufacturer correctly designed and manufactured the hardware to position and aim the feedhorn and included scalar to properly illuminate the reflector surface.

Of course, companies worked very hard and invested lots of resources to design and produce their products. We, amateurs (I suspect majority of users, including me, are such) do not have so much possibilities. All we have is to enjoy what is already done by manufactures.

the photos appear to accurately depict the feedhorn aiming that I have observed on these models during service calls.

Those are pictures of my dish, and that be issue of only my antenna. Situation on another same antennas could be different.

commercial grade reflectors typically have a much more accurate surface than a consumer model. I agree that if all things were equal, the performance would be similar, but they are usually not equals...

Perhaps it is also good to remember that all plastic dishes have metal net inside, eyes are small but, anyway it is mesh. So, that could be possible that noname solid dish, which is in perfect shape (at least when it is new) can also outperform some branded dish. I do not exclude this possibility.

So, I will probably do some experiments soon, like check system performance when LNB is pointed to the very center of the dish and when it is pointed to where it should be pointed according to what I was explaining in this thread.

 

[RimaNTSS]

CM wouldn't have been included the group of the most relied upon dish manufacturers to supply, worldwide, commercial and military needs.

Nobody is perfect, including CM producer. And, maybe not only CM, but another producers made same mistake, for example Northern Satellite Courp (West Germany company), their dish I have here also points LNB to the center of the mirror.
I think that only experiments can prove something here.
Still do not have any answers from CM.

 

[RimaNTSS]

This is not CM1,2m but NSC 180cm dish. Just would like to show where it's LNB is pointed- about 138mm lower than calculated place. However I am not sure is this LNB holder is original one. But this holder was used by previous antenna owner.

 

[FaT Air]

That holder looks DIY. Found this: http://www.satelliteguys.us/xen/threads/northern-satellite-corp-nsc-18-1.189113/
To me that holder looks 'factory' and aims quite a bit higher.

 

[RimaNTSS]

That holder looks DIY. Found this:

I also think it is DIY. And I've seen that thread.
BTW, I have such a holder, it is only belonging to same brand dish Northern Satellite Corporation, but only 1,2M.

 

[Trust]

I've tested several brands offset dishes with my adjustable rotating laser . ( see my channel for more )
The choosen 78 º angle suppost to be the openings angle of the LNBF , as you can see , a lower section of the dish is out of the lnb reach .
The lnb aiming point of this Echostar 120 cm dish was exactly in the middle .
This phenomenon i noticed with a lot of brands but I found also dishes were the aiming point was a bit lower .
The Polish firm , LAMINAS made the OFC-1200 cm plastic dish with 3 alu tubes and about the same plastic lnb holder like the CM , so the position of the lnb is like the manufacturer designed it .
The rotating laserspot adjusted at the top edge and after turning downside the spot was passing 8 cm above the lower edge .
Because consumers complained about that lnb holder (no C-band lnb possible) Laminas made the OFC-1200P 2 treaded rods and a plastic feedarm .
Did the same laser rotating test and at this type the spot was passing 21 cm above the lower edge , and the lnb aiming point at that dish was above the middle (strait laserpointer)
So I made a adjustable lnb clamp to point the lnb lower , the signal level did realy get higher .

 

[polgyver]

Brilliant job, as you tested many dishes ( I tried just two ). To avoid up- and down movement of LNBF "throat", when adjusting the angle, I suggest making simple holder for LNBF, shown in photos below.