Waveguides - do they need to be 'terminated'?

[Shawn95GT]

I want to play with the waveguide that came with my last dish. The waveguide is setup so that the H and V go to seperate LNBs. I only have 1 LNB (the other was a transmitter, and I've since shipped that off to an interested party). Can I leave the waveguide opening open where the #2 LNB would go or do I need to block that off? Will foil tape suffice?

I worried about it from an RF point of view. I'll keep out the elements by other means (may end up taping it up anyays!).

This is the waveguide with the LNB / transmitter attached:

http://www.satelliteguys.us/attachment.php?attachmentid=4807

I have the LNB where the transmitter was (vertical polarization). I want to nail G10R with the optimised feedhorn etc on my #2 dish.

Thanks All,

 

[rkrenicki]

I have some C120 caps here if you want em.. just pay shipping..

But all in all, I would remove the waveguide alltogether, just mount the lnb directly to the feedhorn. Take off that filter too, if you still have it attached.

 

[Shawn95GT]

The bolt pattern on the LNB is different than the C120 pattern. I'm effectively using the straight through section as a C120 feedhorn to LNB adaptor I believe this will only be good for verticle polarized transponders but that's perfect for my experiment.

This is mostly so I can do something with the dish until the QPF-031 LNB is readily available.

I was trying to figure that piece in front of the LNB (in the pic) was. It just seems to make for a very narrow path for the waves to pass. I'm sure as a filter it served a purpose in the wireless Internet application . I'll be sure to lose that.

Will the open hole need to be capped to function correctly or is it mostly to keep the bug / elements out?

Shawn

 

[rkrenicki]

Its a notch filter, so that the transmitted signal does not overload the reciever.


The caps I have here have a different metal in them, probably some sort of rf absorber, I really cant tell, but that LNB definately looks like a C120.. just a single polarity C120, so 4 screws in a square, instead of 8 in a circle.. assuming that the feedhorn is a normal C120 flange, it should match up with 4 of the 8 holes., the other 4 holes should be at a 45 degree angle.

 

[Shawn95GT]

Its a notch filter, so that the transmitted signal does not overload the reciever.


The caps I have here have a different metal in them, probably some sort of rf absorber, I really cant tell, but that LNB definately looks like a C120.. just a single polarity C120, so 4 screws in a square, instead of 8 in a circle.. assuming that the feedhorn is a normal C120 flange, it should match up with 4 of the 8 holes., the other 4 holes should be at a 45 degree angle.

The feedhorn side is just a disc - no holes.

It has two c-shaped sections that clamp the feedhorn to the LNB. The bolt spacing won't work with the four-bolt flange on the LNB side.

I'll take it all apart and try again - and take some more pics (of course!).

Shawn

 

[rkrenicki]

odd.. you may need to rig up something then.. since the waveguide will limit you to one polarity when you get the invacom..

EDIT: wait.. is that QPH-031 the C120 one? or the Circular/Linear one?

 

[Shawn95GT]

odd.. you may need to rig up something then.. since the waveguide will limit you to one polarity when you get the invacom..

EDIT: wait.. is that QPH-031 the C120 one? or the Circular/Linear one?

The QPF-031 is the C120 flanged quad polar LNB. Invacom is cranking out the QPH's right now since the market is much better for 'em. I'll be ordering / pre-ordering my QPF as soon as someone is selling it .

The Feedhorn / Feedhorn end of the waveguide is a C120 flange. The LNB end of the waveguide is whatever that four bolt flange is called.

I'll ditch the waveguide when I get a proper C120 flanged LNB.

Shawn

 

[rkrenicki]

hmm... then I do not know I was under the impression that the round C120 was just basically two of the square ones at a 45 degree angle from eachother.

All I have here is the square stuff.. but yes, I can provide a cap for you if you want it. just pay whatever shipping.

 

[Shawn95GT]

Pics

Pics!

I lined up one side of the C120 clamp with the four bolt flange to show how close it is - but not quite right.

I'm going to leave the filter on for now. I can get tape / stickey all over the end of it and I don't care .

Shawn

 

[Tron]

Shawn, the square mounts for the LNB's look like WR-75's. As for the actual interface between the waveguides and the feedhorn, I don't know. When it was assembled it looked like C-120, but now that it's taken apart it doesn't look that way.

EDIT: It's possible the split circular mount on the feedhorn attaches the feedhorn to a C-120 LNB...

 

[Shawn95GT]

EDIT: It's possible the split circular mount on the feedhorn attaches the feedhorn to a C-120 LNB...

That's what I'm thinking.

Pics are of it mocked up for test. The new color blends much bettter with my wall. The flash picture doesn't do it justice. You can see my quite cheesily mounted ASC421 on my motorized dish too - lol.

Thanks!

 

[Stefan]

"That's what I'm thinking."

Your thinking right. That's the way the feedhorn attaches on all of the oval primestar dishes or at least all the ones I've seen. I think the idea is that the split ring design allows for easy skew adjustment on fixed dish installation which of course is the way the primestar dishes would have originally been used. Youd simply loosen the bolts a bit then twist the LNB to adjust skew. In fact there are markings on one of the split rings to indicate the amount of skew. Anyway, the split rings and feedhorn form a standard C120 flange. Those 2 parts of your assembly appear to be the same as the standard parts used on the oval primestar dishes. The rest of your assembly is different from what youd see on a "stock" primestar but should work.

As for whether or not you need a terminator on the other waveguide, I'd say probably not. Ideally you might want to terminate an unused waveguide but in this situation I don't think it will matter because I believe the other waveguide is probably designed to only accept signals of the opposite polarity. Therefore I think that if you did get reflected waves from the impeadance mismatch caused by the waveguide not being terminated, those reflected waves should not interfere with the signal being recieved by the LNB on the other flange as they will be of the wrong polarity and should get filtered out. So, I think it will work okay.

As for the square LNB mounitng flange, it's a WR75 flange which is what's commonly used for Ku LNBs on BUDs. If you ever pick up another wr75 LNB, you can probably attach it directly to the 90 degree elbow and get each polarity on a separate LNB as shown in this pic I have attached. Pardon the image quality here. The sun was in the wrong place at the wrong time. Of course the easiest route would simply be to attach a C120 LNB directly to the feedhorn as you've indicated you eventually plan to do.