DMX741U issues

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tester239

SatelliteGuys Family
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Sep 27, 2008
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I just got my DMX741U LNB in the mail a few days ago, and installed it on my 10ft KTI dish.. It didn't come with a manual or any papers telling me which port on the diseqc switch went to what band :( -- but this forum had the answer :)

The issue I'm having now is that... Ku band reception sucks! But C band works amazingly well. Is this a sign of improper installation or a problem with the LNB? I figure if C band works just fine and Ku doesn't, that there's something wrong with it...since they're all built into the same assembly.. Ideas?

(Yes, using my other Ku band LNB I get good reception so I know it isn't an aiming issue, and that the dish works with Ku band.)

Fortec Lifetime Ultra setup:
diseqc 1: C band, LO 5150, standard
diseqc 2: Ku band, LO 9750/10600, universal
No switches, straight single line to the dish.
 
I have had just the opposite. Ku works great and C is almost non-existent. Of course I have not done any fine tuning yet. It is pretty much as it was when I pulled the old 621 out and slid the 741 in.
 
It takes some time to get the it set just right.

Make sure the Skew is perfect. I put the Dish at True South, popped the Cap off (push it in to remove), stood behind the Dish and made sure the 1/4" Rod inside the Feed was Horizontal to the Dish.

Put the Dish on a Sat the has both C and Ku, and you can easily reach from ladder. Mine was 125 west.

When I first installed a Combo C/Ku (BSC621) I measured and re-measured with poor results.
For me, I got the best results doing it the hack way:
I set the Feedhorn square to the Scalar Ring, about 1/2" past the Scalar.
Loosened the Scalar Ring bolts and wiggled it around until Quality Jumped.
Slowly tightened everthing up.
At 125 west AMC 21, on the Diamond 9000(retired), I had Q80 for 12180 and Q 72 for 12140.
 
So, I've been outside fiddling with it for a few hours... and I've managed to make C band quality numbers awful, but Ku work "better." I still have gotten better quality numbers on my 3ft dish for Ku. I think I just need to keep playing with it.

Lak7: removing the plastic cover certainly helps with alignment :) However, I noticed there's a huge metal rod in the way of the fingers for the Ku band part of the LNB.. I wonder if this could be causing less-than-optimal numbers? I can't imagine such a huge design flaw existing without _everybody_ complaining.

Also, I don't think my stb understands the concept of 100%.. I've had it go from 10% to 99% without touching anything.. and many times it will say I have no signal quality at all, then all the sudden it jumps to 99% and locks on. ?!?! When I get my new DVB-S/S2 pci card in the mail maybe I can get more reliable quality numbers..
 
I still have gotten better quality numbers on my 3ft dish for Ku.
Click to expand...
LOL
I was expecting the same at first, not going to happen.
Remember a 10' BUD may be Ku "compatible", don't think it's going to out perform a 36" solid Offset Dish. Just like a 36" "can" get C Band, but you are not going to pull in ABC HD on it.
My 80cm outperforms my BUD at Ku, until there is bad weather, the BUD will hold the signal longer.

I noticed there's a huge metal rod in the way of the fingers for the Ku band part of the LNB
Click to expand...
That is the Isolation Bar, needs to be where it is.

What kind of Q are you getting on AMC21 @ 125 west, the PBS stuff?
That is what I'm most familiar with.

If you just want to win the "Quality" race, get a Orthomode Feed with Top Nothch LNB for the tune of $300+.
The DMX741, along with BSC621 and CK1 will give you Good Reception for about $50.

Another thing is Dish alignment. My BCS621 has about a Thousand "set screw" marks in it from tweaking. I was tweaking the wrong thing. Should have tweaked the Dish. A couple of Face Nut turns (1/6th turns) made a huge difference for me.
When I replaced the BCS with the DMX, it took about 1 minute, with improved performance.
 
Face Nut screws? What are those? Also, I can't get 125W because of a tree... but I'll be fixing it's wagon here soon..

After fiddling with it some more, I've gotten some better numbers.. I suppose I had unreasonable expectations for Ku
 
Well, I've managed to get C-Band working pretty damn well with the LNB... but Ku is still awful. On Galaxy 19, everything on C-band pushes 80/90% on quality, but on Ku most of the transponders are just unwatchable, hovering anywhere from 10 to 40% quality. I'm wondering if the jumper wire they gave with my LNB is bad, I'm going to try replacing it after work and see if that makes a difference. Do I still have unreasonable expectations for this LNB or am I still doing something wrong?
 
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on 3990 i'm getting 90% quality, and on 12146 i'm getting 40% AT BEST. This is even with plugging the cable directly into the Ku band lnb, bypassing it's internal switch. I've stopped worring about tracking the arc correctly for the time being and dicked with the elevation and azimuth. I re-adjusted the LNB in the ring before doing any of that to properly peak on C-band.. so I know I'm pointing in the right freaking direction too. What am I doing wrong? Is it time to complain to the vendor?
 
I have a Geosat Pro CK1 on my 10 footer, and C-band is awesome, but on Ku AMC-6 NBC mux is about 60% when it's at 98% on my 1.2m Primestar. From personal experience, I don't think BUD's, and Ku, go together too well.:rolleyes:
 
IMHO:

tester239 said:
I just got my DMX741U LNB in the mail a few days ago, and installed it on my 10ft KTI dish..
The issue I'm having now is that... Ku band reception sucks!
But C band works amazingly well.
Is this a sign of improper installation or a problem with the LNB?
Click to expand...
Based on what I have observed, not personal experience, I'd say it's an installation problem.
Tweaking up the Ku properly, is a critical job.
I figure if C band works just fine and Ku doesn't, that there's something wrong with it...since they're all built into the same assembly.. Ideas?
Click to expand...
No, I disagree.

I've been reading the fine print and taking the pulse of CK-1 and DMX741 users, and -some- BUD users can tune Ku well enough to squash 1m Ku dishes. . .
. . . given time, proper technique, and a decent dish.

A few of the considerations:
- string test the dish
- measure to locate the LNBF at the focal point of the dish and set F/D
- measure to locate the LNBF equi-distance from the sides of the dish
- laser point the LNBF to the center of the dish
- make the scalar square to the dish
 
Alright, it's been a while, and I've been playing around with this thing A LOT.. swapping LNBs and scalar rings, and moving and adjusting everything in sight. I finally caved and went to the local satellite/wiring store in town and got a used Chaparral Corotor with LNBs (made by drake, C band NT: 50K, Ku Band NF: 1.1dBm). I hooked it up to my Chaparral Monterey 100c IRD and had my dish pointed at 99W 4020 V, set the polorotor and BAM! analog channel comes in... fuzzy, but good audio. So, i figure analog is pretty damn touchy when it comes to alignment.. so I've gotta be pretty darn close to spot-on 99W. I whip out the digital box and do a blind scan on both C and Ku, quality numbers are amazing on C-band, and on Ku, they are almost up to the same amount I got with the 3ft metal dish I have sitting ahead of the big dish. I don't even think these LNBs that came with the Corotor are phase stable?!! The Ku band LNB is off by -8Mhz, whereas the C is off by 1.5-2Mhz. I think there's something wrong with the new LNB I ordered (DMX741U).... what do you guys think? I'm still not convinced it's the LNB... I mean, I'm still a bit of a greenhorn when it comes to the big dishes. pics of the new setup to come..
 
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