Linear vs Circular Invacom Issue

H

HDTVFanAtic

Thread Starter
SatelliteGuys Pro
May 23, 2005
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This would probably be better in the FTA section, but apparently the moderators don't think I'm l33t enough to post there, thus I will post here and hope that the smart people actually will see it.

I put in a 1.2M 1130 Prodelin this week with an Invacom QPF-301 connected to a WR75L feed horn that came with the Prodelin Dish and NPR from a local college.

After a very uneventful install, I first wanted to test out my 2 problem birds, 82W and 148W.

Much to my surprise, I could not get a blip.

I then did a sweep of the sky and didn't really find anything. Assuming the meter or the cable must be bad, I went ahead and changed both.

Still no signal.

So I started a very slow and methodical search of the sky to find anything.

Finally in a very small precise location I found 91W. Moving on I was able to locate 101W, 110W and 119W. There was not a lot of spill over in these signals, which I assumed was because it tightly focused the beam.

So I went ahead and threw 119 into a Dish and Directv STB. Surprisingly, the signal was less than my .9 Toroidal with a 0.6 lnb. As it turns out, the signal is even less than a Dish 500 on 119.

Obviously when the signal is that attenuated, I am not going to see 82W or 148W as the idea was to see what signal I could get from them - not fight to get 101,110 or 119W.

I have spent the day corresponding with a number of commercial satellite installers (IE, not the $50 per install Dish/Directv idiots).

After thinking about this most of the day, they believe that possibly, the WR75L is primarily for linear and I was trying to pick up a circular bird. 99.9% of their customers use the Linear feed and the circular is "Just because they can".

Could the circular part of the INVACOM be attenuated by the rectangular WR75 opening in the flange.

Would it make any sense to try and loose the Linear opposite rejection part of the feed by ROUNDING out the flange to match the opening in the INVACOM LNB.

The metal is very soft and can probably be filed or even cut with a utility knife.

I guess I could order a circular feed horn from Prodelin, but then again, nothing from Prodelin is cheap - and most likely I would say 'I could of done that !" when I the other.

I have seen some older feed horns before they built the linear rejection into the flange that people used to put a donut into the opening for orientation to Linear. If you leave out the donut it's a Neutral or a Round piece of pipe so to speak.

Is there any logic to this or does it sound like a bigger issue somewhere?

I really wanted to use this dish to lock in 82W and/or 148W, as well as 89W Linear, which brings up the next question. What motor and controller assembly would I need for the Prodelin 1.2 Meter? Dish specs are here.

Thanks.
 
DSSJAKE

DSSJAKE

New Member
May 16, 2006
4
0
Planet Earth
HI there. My 2-cents.

When I was setting my first AlphaStar STB, it comes with that LNB Ku-linear.
Intructions ask to tilt the LNB some degrees on its bracket.
This tilt is named SKEW. This value is fixed by GEO location.

Hope this helps. Enjoy !
 
Bountykiller

Bountykiller

Pub Member / Supporter
Feb 22, 2004
379
0
Your using the wrong horn it sounds like. I use a QPF-031 on a 1.8 meter Channel master and the signal is sick compared to an el cheapo Echostar LNB etc. Your horn should have NOTHING in it at all. no grooves, no things sticking out etc and should be circular inside. If not, you likely have a linear horn. You can convert it using a polarizer but you lose .1 db doing so. I would advise finding a circular horn. Trust me, when this is set up right, theres no question of the signal improvement.

-B
 
Last edited:
H

HDTVFanAtic

Thread Starter
SatelliteGuys Pro
May 23, 2005
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As stated, it is a linear horn, thus the L designation. Most customers for dishes of this size are using linear anyway. Heck, prior to yesteday, I could not even begin to tell you that the small portion of the feed in the waveguide had to be round for circular polarization and rectangle for linear. I seriously doubt that 1 in 1,000 people here (maybe 1 in 100,000 lol) knew this.

As also noted, it was suggested that I file the waveguide to make it circular instead of paying a sick amount to purchase a circular one as someone that deals with these things says its a relatively easy process.

Supposedly that process (or by logical extension, a new WR75C) would not have the linear opposite rejection if I did this as the waveguide was made round for an inch. Howeer, I have no idea how important that is in the first place.

I guess I am just somewhat (no make that VERY SHOCKED) that a rectangle shape vs a round hole over 1 inch has this DRAMATIC effect as I have never seen a problem like discussed by anyone on any of these forums - so I am taken back and wondering if the whole scenario sounds logical. I know the old square peg, round hole scenario, but we are talking about a hole, lol....and radio waves which one would not think as physically solid as a square peg.
 
Last edited:
Doctor Bob

Doctor Bob

SatelliteGuys Pro
Nov 22, 2003
566
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Riverside, California
HDTVFanAtic said:
This would probably be better in the FTA section, but apparently the moderators don't think I'm l33t enough to post there, thus I will post here and hope that the smart people actually will see it.

I put in a 1.2M 1130 Prodelin this week with an Invacom QPF-301 connected to a WR75L feed horn that came with the Prodelin Dish and NPR from a local college.

After a very uneventful install, I first wanted to test out my 2 problem birds, 82W and 148W.

Much to my surprise, I could not get a blip.

I then did a sweep of the sky and didn't really find anything. Assuming the meter or the cable must be bad, I went ahead and changed both.

Still no signal.

So I started a very slow and methodical search of the sky to find anything.

Finally in a very small precise location I found 91W. Moving on I was able to locate 101W, 110W and 119W. There was not a lot of spill over in these signals, which I assumed was because it tightly focused the beam.

So I went ahead and threw 119 into a Dish and Directv STB. Surprisingly, the signal was less than my .9 Toroidal with a 0.6 lnb. As it turns out, the signal is even less than a Dish 500 on 119.

Obviously when the signal is that attenuated, I am not going to see 82W or 148W as the idea was to see what signal I could get from them - not fight to get 101,110 or 119W.

I have spent the day corresponding with a number of commercial satellite installers (IE, not the $50 per install Dish/Directv idiots).

After thinking about this most of the day, they believe that possibly, the WR75L is primarily for linear and I was trying to pick up a circular bird. 99.9% of their customers use the Linear feed and the circular is "Just because they can".

Could the circular part of the INVACOM be attenuated by the rectangular WR75 opening in the flange.

Would it make any sense to try and loose the Linear opposite rejection part of the feed by ROUNDING out the flange to match the opening in the INVACOM LNB.

The metal is very soft and can probably be filed or even cut with a utility knife.

I guess I could order a circular feed horn from Prodelin, but then again, nothing from Prodelin is cheap - and most likely I would say 'I could of done that !" when I the other.

I have seen some older feed horns before they built the linear rejection into the flange that people used to put a donut into the opening for orientation to Linear. If you leave out the donut it's a Neutral or a Round piece of pipe so to speak.

Is there any logic to this or does it sound like a bigger issue somewhere?

I really wanted to use this dish to lock in 82W and/or 148W, as well as 89W Linear, which brings up the next question. What motor and controller assembly would I need for the Prodelin 1.2 Meter? Dish specs are here.

Thanks.

You have put yourself above the, as you put it "(IE, not the $50 per install Dish/Directv idiots)" and yet you are shocked that 1" from round to rectangular has such a hugh difference??? What is that all about???

You are using the wrong feed horn!!! Go back to basics, "Plan your work, then work your Plan"... Such a long disertation, about such a short subject, suggests that you simply have an ego problem, nothing more, and nothing less!!! :D
 
M

Mr Tony

SatelliteGuys Pro
Supporting Founder
Nov 17, 2003
372
103
Mankato, MN
This would probably be better in the FTA section, but apparently the moderators don't think I'm l33t enough to post there, thus I will post here and hope that the smart people actually will see it.
yes this would be better in the FTA area. I don't understand why you feel you can't post there.
"smart" people? Sounds like someone has an issue with the FTA'ers
 
Bountykiller

Bountykiller

Pub Member / Supporter
Feb 22, 2004
379
0
Hah ;0 HDTVFanatic, it makes sense when you think about it. No the right horn is not much at all. Find a dealer for those dishes and they will likely just give it to you. I have about 5 or 6 for my Channel master 6 footer. They are *VERY* common and in the fringe areas of any beam theres many people using these large dishes for dish and Directv etc. They are not un-common at all. You would be surprised.

-B
 
H

HDTVFanAtic

Thread Starter
SatelliteGuys Pro
May 23, 2005
1,973
0
Iceberg said:
yes this would be better in the FTA area. I don't understand why you feel you can't post there.
"smart" people? Sounds like someone has an issue with the FTA'ers


Oh really?

I see this and notice FTA stuff being marked Private Forums.


















And if I go to FTA Section I get this:





















So you tell me, since I have requested to be able to access it multiple times to you and the other mod, how should I take it?


Sounds like your problem is with me, not me to FTAs.
 
H

HDTVFanAtic

Thread Starter
SatelliteGuys Pro
May 23, 2005
1,973
0
Doctor Bob said:
You have put yourself above the, as you put it "(IE, not the $50 per install Dish/Directv idiots)" and yet you are shocked that 1" from round to rectangular has such a hugh difference??? What is that all about???

You are using the wrong feed horn!!! Go back to basics, "Plan your work, then work your Plan"... Such a long disertation, about such a short subject, suggests that you simply have an ego problem, nothing more, and nothing less!!! :D


Every $50 per install former Radio Shack minimum wage Dish/Directv installer would not even know that there was a difference in linear vs circular lnbs, much less what a waveguide is as they have never popped open an lnb.

If I personally knew all the answers, I wouldn't have asked it would I?
 
M

Mr Tony

SatelliteGuys Pro
Supporting Founder
Nov 17, 2003
372
103
Mankato, MN
That is due to a glitch in the system. I already talked to Scott about that a while back and its a bug.

If the last post in the FTA area was part of the "Whats Up there" area, it shows "Private Forum". I do not know why it does that and like I say I had Scott look at it and he says its a bug in the software. If any other post is the last one, you don't see that and it shows the last post.

Anybody can see the main FTA area regardless of what the "last post" showed just by clicking on the main "FTA" link there. Its not you, its the system. :)
 
M

Mr Tony

SatelliteGuys Pro
Supporting Founder
Nov 17, 2003
372
103
Mankato, MN
please see attached photos.

I updated a thread in the mian FTA area to make it the newest and logged out so I was a guest. If you see the 2nd picture, it shows the last post was mine that was updated. :)
 

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