aiming a 6 footer with DMX741U

Status
Please reply by conversation.

icu1954

SatelliteGuys Pro
Original poster
Sep 1, 2010
275
0
lower alabama
i will be putting my 6 footer on the pole today if weather permits.It will be stationary for the time being,i have a dmx 741u that i have heard so many negative things about the KU side being pissy,so is it wise for me to try and aim on a cband transponder rather than a ku to keep my frustration and blood pressure down.Also what is the hottest cband transponder for 91.0 west ?
 
Last edited:
I think the FOX TPs are the hottest
3820 V 30000
3860 V 30000

Start with C Band, then move to Ku.
Keep in mind that you are using a Universal Ku LNB, so set the L.O.s properly, and use known hot TPs when tweaking / aiming.
 
I have a 6 footer with a standard dmx 741 and i can say it works very well on both c and ku on the majority of satellites i can get.One thing though!! It did take alot of trial and error to get the 741 setup for good signals on both c and ku.
 
could you give me some pointers for this 741u,i don't know how i could set the skew there are no marks to go by,when i place it in the scaler i have 0 setting turned to 12 o'clock,was trying to get 91 west with a skew of 4.2,didn't have any thing to go by.
 
Depends on the Dish.
If there is a way to stand behind the Dish and look up into the feed horn, do that. Remove the feed horn cap, and you will see a 1/4" metal rod. The rod should be Horizontal when the Dish is at your true south sat.

If you can not do that, then the "0 to the Dish's 12 o'clock" will get you going, just tweak for Ku.

If I were to guess, 4.2 degrees would be like the thickness of the stamped "0".
 
I never took the cap off mine!at the time i didn't know this could be done.What i did was first find out the f/d ratio of my dish which is about .36 I first installed the 741 into the scalar ring with the 0 marking stamped on the end facing straight up and the 4 marking showing on the side just inside the ring.This gave me maybe a inch of the 741 sticking out the other side of ring.In my case my i had a good view of the tv from the dish.I don't really remember if i started with c or ku but since ku is harder to align i would start with c.Move your dish to your true south satellite!pick a known active TP and start with that.Since you have a universal 741 set the receiver setting to universal!in my case i would set it to 5150.I found that its very important to make sure your dish elevation and really being on the satellite you want!or you can play with the 741 all day without getting any good Q sig from the tp you want.I also found out that even when my dish was aligned correctly i didn't get any Q from the starting point on my lNB setup.While watching the tv i started to rotate the 741 cw or ccw slowly till i started to get some signal and a lock on the tp i was looking for.After maxing out the signal by rotating the 741 i would mark its location with some tape or a marker!a pic would help also.I did this because if i started tweaking again i would have a good idea where i started at.I would then slowly move the 741 inwards of outwords looking for the best Q then checking to see if my 741 was really hitting a bullseye to the center of the dish.slowly tighten the set screws! NOT TO TIGHT! because that could throw off the alignment.I found that this was no guaranty that when checking out the ku after it would work just as good as the c.I had to go back and forth with between c and ku with some tweaking till i got a peak sig on both.Here is a pic of mine! you can tell how much playing with it i did before i got good results.
 

Attachments

  • 506.jpg
    506.jpg
    275.5 KB · Views: 212
hi, stanleyjohn..does this mean that although my dish is stationary,i still have to go to my true south and set the lnb to 0 at 12 oclock and try to get a signal on my true south sat,then move to the satellite i am looking for and try to get a signal with the lnb still at the 12 oclock position and if i get a signal start adjusting the lnb from there?
 
Hmmm! Wish i could give you an answer to that since i have only worked with a motorized dish following the arc.I'm not sure on this but i would think that the same would apply to a non motorized dish but if I'm wrong i hope someone here will correct me.I think a stationary dish would follow the arc just like a motorized one!the only difference is the stationary one you need to move to another satellite manually.
 
I think it was BJ the one who gave an explanation on this but I can not find the thread now. Most stationary dishes have a Az/EL type of mount not a polar mount. In the Az/EL mount case then you adjts the AZ and EL and then skew the LNB inside the scalar to peak signal.

But more likely the OP has a polar mount dish (that will be motorised later) in that case then you do what Stanley says. Position the dish at true south as if it was going to be motorised (use a pipe as an arm) and set the LNB at 0 skew, therefore when you move the dish to the intended SAT or if you install an arm later it will be properly setup. Of course in that case for you to find the SAT you will have to use a pipe (to function like an arm) and use that pipe to push or pull the dish accordingly instead of rotating the dish mount on the big pole.

Most polar mounts comes with a fixed length plate that replaces the arm , if you want to use that then you need to treat it "similarly" to an AZ/EL mount explained earlier. For that you adjust the EL and rotate the dish mount to the proper AZ for the intended SAT and then skew the LNB accordingly.

Hope it makes sense.

BTW Stanley, Would you say that on the picture your LNBF is set for an f/D of .36? The 6ft dish has a .38 f/D and in my case the freaking Gospell LNBF, the Scalar is all the way to the back stopped by the C rectangular LNB (better if I grind the Scalar to move it further back) for peak signal on C and Ku (still LPBS issue but even C27 on 53W behind the tree works)
 
Last edited:
thanks hdfan,now could you tell me how to measure my focal distant in inches..from what point at the lnb to what point on the dish? not good with the metric system thats why i need this in old american inches (smile)
 
BTW Stanley, Would you say that on the picture your LNBF is set for an f/D of .36? The 6ft dish has a .38 f/D and in my case the freaking Gospell LNBF, the Scalar is all the way to the back stopped by the C rectangular LNB (better if I grind the Scalar to move it further back) for peak signal on C and Ku (still LPBS issue but even C27 on 53W behind the tree works)

In my case i im not really sure if my LNB is set for .36.I figured that the markings on the side of the 741 showed the ratio! 2=.2,4=.4 and so on and set the distance using these markings.After making my adjustments this is where i found c and ku works its best.ICU1954! there are ways to measure the f/d and its been posted here before! im sure someone will come to the rescue.
 
no, .2 meaning 0.20 and .4 meaning 0.40 would be more separated that what the picture shows. on top of that 0.42 would be closer to the LNBF edge (as per chaparral the feed edge is almost flush with the scalar) or openning than 0.2 (if a feed with a 0.2 setting even exist, the lowest f/D ratio for a Dish i have read or heard is .275). more likely they represent .32 .34 .36 .38 .40 and .42. The reason I ask is to compare to my gospell , unfortunaelly (or fortunaelly) it works very well but in a position where if pendragon sees it he will have a heart attack!, lol. The LNBF is All the way in and can not go in further because the C LNB hits the scalar and it is not even straight and that is what bothers me even more!. It is driving me crazy now all this but heck even LPBS works at night if I bump the dish upwards just a bit. I guess the Gospell LNBF has its focal point way inside its throat!!! (it acctually has another one half way but 8PSK ku reception is not as good as a 90 cm dish so I kept pushing it inside)

icu1954. f/D can be calculated but more likely your dish documentation has that value or you could find it on the internet using the dish model number. f = D * D / 16 * c where c is the distance from the dish center plate to the imaginary line that goes from edge to edge . D is the diameter and f focal length. all measurements have to be taken using the same metric system , either international or US. i go by memory so maybe i am mistaken , please check it online.

As per chaparral (valid for chaparral feeds that is) the focal point of the feed is just 1/8" away from the feed openning. So you will have to adjust the feed 1/8" "edge" to match the dish focal length. every feed is different as it depends on its geometry (pyramidal type feeds has their focal point even further inside). the focal point of a dish is always meassured from the dish center and perpendicular to it. unfortunaelly i do not think this LNBF's have any documentation that clearly states where its focal point is , at least not my Gospell. you are lucky yours at least has f/D ratio markings , mine barely has the skew setting and it is 90 degrees off!, lol. I am not good with the US metric system and probably 99% of the world isn't either!.

To adjust the feed to match the dish focal point you can not move the feed in an out , it has to be the whole Scalar/feed assembly because the Scalar has to be set for .38 always (it determines how wide the "illumination" angle is) and that is why pros like pendragon fabricate custom feed arms or holders that allows them to move the scalar/feed together in or out. but in any case trial and error has always been the best friend of the americans since the first immigrants arrived to this land so keep trying till it works best no more.

I do not think right now there will be an 8PSK signal on Ku that I can not watch (other than LPBS at night) with the 6 footer / gospell C/ku LNBF combination but will have to wait a bit more since I just adjusted the feed very recently. As per C band , Africa Channel on 133W comes in fine and Fox Sports HD en Espanol on 55.5 W as well plus any 8PSK with a 3/4 FEC or lower. I get some 5/6 8PSK's but I dont think I get all , higher FEC are a no go so far. no problem with the highest DVB-S FEC's signals and no problem with cross polarisation anywhere (probably 58W most critical since it has to equal signals on different polarities). Obviously it is just a 6 footer so adjacent interference is an issue but signal strenght or quality wise it performing great. I dare to say that even better than most 8 footers out there.

What i am trying to say and insist on is that the most important factor is not the LNB's specs but rather the dish mount aligment and even more critical the feed/lnb aligment as well. most people have issues due to poor aligments not because they use LNBF's made in china or because the dish size (heck back in havana the feed horn was acctually a popular oil metal can that contained vegetable oil that Italy had donated to Cuba and its size was a perfect match for a 2.4 Ghz MMDS service that had 11 analog channels for Havana hotels, ESPN, HBO , Cinemax , CNN and the likes).

Of course once you peak your dish to the maximum I bet we will all want bigger dishes or Norsat's LNB's and Chaparral ortho feeds to get that other fringe signals we dont get due to phase noise or not enough gain.
 
Your welcome but make sure your aliNgment is way better than my spelling of it on the previous post!, lol. Not once , nor twice but five times or more misspelled!. lol.
 
hi,stanleyjohn i want to make this as short as possible.been trying to aim 6ft special with dmx741u,settings in box correct,elevation correct,lnb installed correct etc. etc. etc....no signal,been munipulating lnb with in and out of the scaler,turning lnb cw and ccw...no signal...been checking el and az no signal.hooked signal finder up and turned to my true south galaxy 28 and strong signal from signal finder but no signal shows up on my receiver...with or without signal finder being hooked up.could i have a dead lnb..would be thankful for any suggestions
 
Hi ICU hang in there!ill try to think of some answers for you.Im alittle supprised you havent had much help from other members here but hoping others will help.I have the reg 741! but i cant see any reason why the universal wouldnt work as well.If you really think for dish is setup correctly then it may be time to elimanate possible problems.It may be possible the LNB or Receiver is defective!if you can swap with a known good one give that a try.Make sure the RGU6 cable is making good contact between receiver and the LNB.Thats it for now! time for me to go to work. Stan
 
Status
Please reply by conversation.
***

Users Who Are Viewing This Thread (Total: 1, Members: 0, Guests: 1)

Who Read This Thread (Total Members: 1)