Replacing KU LNB

[Greg Mueller]

I am wondering about replacing the LNBs on my Primestar dishes with more modern, more powerful LNBs. Attached are a couple photos of the existing Primestar LNB. A couple questions
1) Is this a common mounting screw pattern/technique ?

The horn is marked off for skew adjustment

2) Is there a marking on the new LNB for orientation or so you just attach it by visual reference?

3) Would one like this bolt up?
P270 Linear Dual LNBF - FTA LNB's - FREE TO AIR - Volunteer Satellite Distributors

 

[SatPhreak]

1) Yes it is a (semi) common mounting pattern, it is a C120 flange.
2) Visual would be fine since with 8 holes you can only be out 45 degrees.
3) No, that won't work as it is a lnbf (feedhorn is part of it) and that feedhorn needs a lnb such as an Invacom QPF-031 or an Eagle-Aspen P-870. I also believe the linear dishnet lnb from a dish 1000 dish will bolt on.

 

[voomvoom]

The Eagle Aspen P-870 can be found at the bottom of this page:
GLOBAL  COMMUNICATIONS
It is an FSS Stacked lnb and that feedhorn comes with it, but it will bolt up to your feedhorn.

 

[turbosat]

Greg I don't see any reason why that lnbf in the ad you linked to wouldn't work-it has the c120 flange just like the orig primestar lnb. But it looks like a dual output lnbf just like some of the orig primestar lnbfs, a sep line for vert and horiz. And a .8 degree noise figure prob not much better than your orig lnbf. I swapped out some of my primestars with the techsat tracker and tracker 2 models (sold by our sponsors at top of page and other dealers) and they fit right into the feedhorn clamp on my 1m Pstars.

 

[phlatwound]

Greg I don't see any reason why that lnbf in the ad you linked to wouldn't work-it has the c120 flange just like the orig primestar lnb. But it looks like a dual output lnbf just like some of the orig primestar lnbfs, a sep line for vert and horiz. And a .8 degree noise figure prob not much better than your orig lnbf. I swapped out some of my primestars with the techsat tracker and tracker 2 models (sold by our sponsors at top of page and other dealers) and they fit right into the feedhorn clamp on my 1m Pstars.

turbo, do you have a pic of one of your P*'s with a TrackerII installed?

Did you have to remove the plastic cover from the LNBF to make it fit?

edit: I just noticed you were talking about 1m P*'s, mine is an 84.

 

[Greg Mueller]

The part that clamps into the LNB holder is 1.5" in diameter.

Maybe there is an LNB that is 1.5" in diameter that would just clamp right in there.

If that tracker II is the right size maybe it would work.

 

[phlatwound]

The part that clamps into the LNB holder is 1.5" in diameter.

Maybe there is an LNB that is 1.5" in diameter that would just clamp right in there.

If that tracker II is the right size maybe it would work.

Hmmmm, I must have a different clamp on my P*, the LNBF throat where it passes through the clamp is only about 7/8" or so.

I think I've seen at least 2 different feed setups on these dishes, mine has the big oval housing (4" x 8" +/-) on the back of the feed.

 

[Greg Mueller]

If you look at the first picture I posted you can see the area that clamps in the mount. Its on the feed horn right where it stops tapering, between the two ridges. It works pretty slick. To adjust the skew you just loosen the the clamp and rotate the horn. It has markings.

Just to complicate the issue.....

Ultimately I'd like to have the 4 (or more) of the Primestar dishes that I have pointing at different birds and hooked up to one receiver through a switch. So I guess there would have to be a H/V switch on each LNB and the output would go to a 4 input switch of some sort.

Maybe a "Universal" LNB would work better for this type of setup ????

 

[Greg Mueller]

Here's a better picture. This is the one I have in use (different brand used by Primestar). The throat of the horn is slightly shorter on this one, which makes me wonder if the LNB isn't somewhat tuned to the feed horn.

 

[SatelliteAV]

LNBs are not tuned to a feedhorn, but feedhorns and the scaler are optimized for a reflector. The greater the feedhorn length (untuned) and more angles that the signal passes through before reaching the LNB, the greater the attenuation. Attaching a WR-75 type device to a C120 will also result in signal attenuation.

You will not improve the signal quality by replacing a matched feedhorn and quality LNB with an off the shelf LNBF. Even if the LNBF has a lower noise ratio, the mismatched feedhorn will degrade the signal more than the improvement in the NR. You will also find that the original Primestar LNBF will provide a much more stable signal and exhibit higher performance than off the shelf LNBFs.

 

[turbosat]

LNBs are not tuned to a feedhorn, but feedhorns and the scaler are optimized for a reflector. The greater the feedhorn length (untuned) and more angles that the signal passes through before reaching the LNB, the greater the attenuation. Attaching a WR-75 type device to a C120 will also result in signal attenuation.

You will not improve the signal quality by replacing a matched feedhorn and quality LNB with an off the shelf LNBF. Even if the LNBF has a lower noise ratio, the mismatched feedhorn will degrade the signal more than the improvement in the NR. You will also find that the original Primestar LNBF will provide a much more stable signal and exhibit higher performance than off the shelf LNBFs.

brian: u may be right, but some of us do it anyway LOL

 

[gillham]

If you look at the first picture I posted you can see the area that clamps in the mount. Its on the feed horn right where it stops tapering, between the two ridges. It works pretty slick. To adjust the skew you just loosen the the clamp and rotate the horn. It has markings.

1.5" is close enough to 40mm that I would say you probably have the standard 40mm mount on that dish. I would probably bolt an Invacom or Dish FSS LNB to that feedhorn if I was replacing the current LNB.

Just to complicate the issue.....

Ultimately I'd like to have the 4 (or more) of the Primestar dishes that I have pointing at different birds and hooked up to one receiver through a switch. So I guess there would have to be a H/V switch on each LNB and the output would go to a 4 input switch of some sort.

If we just go with the 4 Primestar setup, that is 4 orbital slots, 2 polarities per slot. You can easily do this with two 4x4 or 4x8 (or 5xN) multiswitches if you want voltage switching from the receiver to "just work" with your LNBs.

Basically a 4x4 multiswitch has inputs for the H&V polarities of two LNBs. It uses voltage to select the polarity and 22Khz off/on to select the LNB/orbital slot.
13v/0Khz = slot 1 V
18v/0Khz = slot 1 H
13v/22Khz = slot 2 V
18v/22Khz = slot 2 H

A second 4x4 gets you:
13v/0Khz = slot 3 V
18v/0Khz = slot 3 H
13v/22Khz = slot 4 V
18v/22Khz = slot 4 H

[3rd & 4th can be added as well]

Then you just give each (of up to 4) receiver a 4x1 DiSEqC switch, with port 1 going to the first 4x4 and port 2 going to the second 4x4, etc.

So with normal switching for DiSEQc, 22Khz and polarity you end up with:
port 1 - 00Khz = slot 1 (H&V)
port 1 - 22Khz = slot 2 (H&V)
port 2 - 00Khz = slot 3 (H&V)
port 2 - 22Khz = slot 4 (H&V)

optional:
port 3 - 00Khz = slot 5 (H&V)
port 3 - 22Khz = slot 6 (H&V)
port 4 - 00Khz = slot 7 (H&V)
port 4 - 22Khz = slot 8 (H&V)

If you use 4x4 switches you can have 4 receivers connected to 8 orbital slots! All without using any fancy 8 port DiSEQc switches, or cascading DiSEQc switches. DiSEQc 1.0, 22Khz and voltage switching should work with almost any receiver.

 

[gabshere]

I've mounted several diferent types of lnbfs to the 84e & 1 meter primestars and always came back to the original ( or the hughes type lnb mounted to the feedhorn) just like Sat AV mentioned they are matched ( the dish & feedhorn).

I tried several non c120 flange lnbfs also and with some there was slightly better signals on a few TP and on others slightly worse ..... for the money it wasn't worth it.

now there are the high end c120 flanged lnbs i didn't try like the QPF031 ( its also very heavy) but when matched to the feedhorn from that dish should work very well ....is it worth the extra money .... i don't know $80 + was a lot for me to try just to gain a point or two on Quality

also realize and i think that Sat AV was kinda hitting at this( if not forgive my assumption) .... that the original lnb although its might show a higher noise freq say like .08 or .07 are a very stable lnb and some ( in my experence ) have preformed as well or better than some lnbf's listed at .04 & .03 NF


sometimes in the process of choosing the best lnb the lower noise figure is not everything to consider in the equation. Stability is also something to consider. to build these newer lnbf's Cheaply a lot of companies fudge a little on stability to keep cost down. This is why most of your TV stations prefer a PLL LNB as to the average lnb. they hold a signal.

 

[Mr Tony]

If you use 4x4 switches you can have 4 receivers connected to 8 orbital slots! All without using any fancy 8 port DiSEQc switches, or cascading DiSEQc switches. DiSEQc 1.0, 22Khz and voltage switching should work with almost any receiver.

yep. Use to do that with the T90. 4 receivers seeing 8 LNB's...Also for the OP if you are more of a picture kinda guy here is the switch setup and a pic (courtesy of Anole)

http://www.satelliteguys.us/1344316-post9.html

 

[gabshere]

also to add to this I'm not saying rush out & buy a PLL type lnb for the average person this would be extream overkill. what i'm saying is that every box reads differently and acts to the lnb placed on it. on my coolsat usually with a threshold of 63% Quality and it comes in and out a lot. some lnbf i placed on it preformed well and got a signal higher than some of the older lnbfs but those older lnbf seemed to hold the signal better and in most cases this was due to the stability of the lnbf. now is 93% better than a 85% signal ?? sometimes it is and others it isn't. lots of times i've had the lower stability higher NF lnbf hold the signal while the newer lnbf with a high stability but a real low noise figure lost the signal.
just food for thought.

 

[ACRadio]

The NJR series that PrimeStar used was rated at a .9db noise figure, while the Hughes C120's were rated at .6db...

 

[rv1pop]

I was interested in SatelliteAV comment on the original Primestar LNBF that it works better than substitues. HE SELLS the substitutes.... Now that is integrity!

 

[Mr Tony]

I was interested in SatelliteAV comment on the original Primestar LNBF that it works better than substitues. HE SELLS the substitutes.... Now that is integrity!

Very true....but there is a reason he said that

You will not improve the signal quality by replacing a matched feedhorn and quality LNB with an off the shelf LNBF. Even if the LNBF has a lower noise ratio, the mismatched feedhorn will degrade the signal more than the improvement in the NR. You will also find that the original Primestar LNBF will provide a much more stable signal and exhibit higher performance than off the shelf LNBFs.

when you replace a flanged LNB with a non flanged, I noticed the LNB "eye" is a little higher when placed on it. So those Primestar LNB"s I've seen work just as good as lower DB LNB's....sure they may say a .4 but them P* LNB's hold their own

 

[Greg Mueller]

LNBs are not tuned to a feedhorn, but feedhorns and the scaler are optimized for a reflector.

I thought about that right after I posted. I should have said horn to LNB.

I would stay with the original LNBs but a few of my easter eggs (I mean dishes) did not have the LNBs to start with and one of them did not work. So I have to come up with an alternative.

 

[gabshere]

i suspect this one will fit and is on sale but you would have to ask sadoun cause the cover on it covers up any feedhorn mount holes.

the hughes lnbfs for the directway should also fit. if its the feedhorn you need
i have a couple so if you know the dish # and size we can probably match them up.