circular/linear lnb's

[Vorg]

I have a QPH031 and found it anoying that the circular and linear ranges are not the same. It seems it is 2 lnb's on one feed horn. I was looking at the DMX741U and they claimed it did both circular and linear because of the dielectric plate. Says the same thing on the WS International site, the people who make it. But it's not until you download the manual and go through it that you find it can't do both at the same time as the web sites imply. Now if the QPH031 can do both with the same horn, the DMX741 should be able to also. But I don't understand why the QPH031 needs 2 lnb's to do it. It just doubles the cost. It's not the electronics of the lnb that makes it circular or linear, it's the pickup elements.

So why can't they make a c/ku combo that does both circular and linear by switching the elements instead of swapping lnbs or making you go out side and add/remove a plate to switch? Isn't there a way to convert circular to linear without blocking the linear signals? Then you can have 1 lnb unit with dual outputs or single band stacked output so it can feed more then one tuner at a time.

 

[1ADAM12]

Dielectric plate

The lnbf on the right has the fiberglas dielectric plate inserted for circular.
The lnbf on the left is being used for linear.

 

[SatelliteAV]

But I don't understand why the QPH031 needs 2 lnb's to do it. It just doubles the cost. It's not the electronics of the lnb that makes it circular or linear, it's the pickup elements.

The QPH-031 uses the same probes (pick-up elements) for Linear and Circular reception. The unit uses electronic phasing to select H/V and L/R. When the OPH-031 was designed, it was for a specific use which required the DBS LO to be set at 11250 and FSS to be set at 10750. The unit was produced to be interchangeable for fixed LO of Dish Network and DirecTV receivers.

The C/KU band and C-band LNBFs use mechanical devices called dielectric plates for receiving circular C-band signals. The insertion of these plates do not eliminate the linear signals, but they are attenuated.

 

[guapoharry]

The lnbf on the right has the fiberglas dielectric plate inserted for circular.
The lnbf on the left is being used for linear.

What kind of covers are those on the C-band feeds?

 

[Vorg]

1ADAM12, I'm trying to make this work with one lnb on the end of a home built horn antenna.

Just looked through lyngsat and didn't see a single c-band with circular tp's I'm thinking now, if you can't selectivly convert circular to linear without interfering with the signals that are already linear, maybe build a diseqc controlled device to slide the dielectric plate in/out of the side of the wave guide. Does it have to go in the lnb up close to the pickup? or can it be out in front a bit?

 

[1ADAM12]

What kind of covers are those on the C-band feeds?

Plastic covers from food package. the right lnbf has taken water from back of scalar, needs drain hole.

1ADAM12, I'm trying to make this work with one lnb on the end of a home built horn antenna.

Just looked through lyngsat and didn't see a single c-band with circular tp's I'm thinking now, if you can't selectivly convert circular to linear without interfering with the signals that are already linear, maybe build a diseqc controlled device to slide the dielectric plate in/out of the side of the wave guide. Does it have to go in the lnb up close to the pickup? or can it be out in front a bit?

Well, then there is an improved(?) device for replacement of dielectric.

 

[Vorg]

Looks like a chunk of clear plastic with bits of foil on it. Any details/links to more info?

 

[1ADAM12]

Looks like a chunk of clear plastic with bits of foil on it. details/links to more info?

This may help.
There is another version that does not have the three block sections in the center.
Not tested for both C/L operation but may work.

 

[Lak7]

if you can't selectivly convert circular to linear without interfering with the signals that are already linear

Keep in mind the Plate is for Circular C Band only.

 

[Anole]

here's the answer:

In this thread, we discovered the only feedhorn I've heard of that'll do linear and circular all by itself.
For C-band, only, that is.
The discussion in that thread should help in clear up the mystery.

edit:
If that didn't suit you (and it didn't appeal to me 'cause of cost), Pendragon has posted a thread on how to mount two C-band feedhorns beside each other, one for circular, one for linear.
I've seen pictures by ACradio where he did a beautiful job with two of the bandstacked C-band LNBFs.

 

[pendragon]

Looks like a chunk of clear plastic with bits of foil on it. Any details/links to more info?

You're welcome to try, but the person who has published this across several websites around the world has mysteriously avoided any discussion when queried about the concept/theory behind it. I would be very leery, as it appears on a surface analysis to introduce frequency-dependent VSWR effects. That has been somewhat borne out by independent reports that suggest that when compared to a dielectric slab, some signals are improved by this device while others are made worse.

 

[Vorg]

Keep in mind the Plate is for Circular C Band only.

Well, that's a problem. I thought it took care of both since it is ahead of both lnb pickups. Doing c-band only seems pointless because as far as I can tell, currently, only ku is using both circular and linear. All the c-band channels, fta and not are all listed as linear on lyngsat.

The lnb I was looking at is $50 which Is why I didn't want to use more then one. Might end up going with a guide splitter and then use different lnbs. Haven't looked at the other links posted yet and still trying to find better info on designing the horn.