KU Polarizer/Adapter for C Band feedhorn.

[CharredPC]

Where's it at?

Posted 05-27-2005:

Sadoun will be introducing a new "Prime Focus" C/KU band COMBO LNB. It is an integrated feedhorn, voltage controlled 13/18V C/KU band LNBF. We will be testing the LNBF soon before releasing it to the market. The LNBF will have two F outputs (one for KU and one for C-band). So you will have to use a 2-way DiSEqC switch.

I just thought to let the Satelliteguys members know in advance.

Any word on this? There's at least two or three threads discussing the best way to use both C-band and Ku on a single dish. I'm trying to come up with a way to use my Invacom 0.3dB and the offset C-band lnb together, and it always comes back to the same thing... there is only ONE focal point on a dish. You can stretch it a bit, deal with signal loss and work in parrallel, but the bottom line is that if you want to get the most out of your dish, use a single lnb at the prime focal location. In my opinion, the only thing lacking in our MicroBUD setups is dual band compatibility. And no, I don't count using archaic 10-12' prime focus BUD co-rotor

Anything? Anyone? (echo, ehco, echooo....)

 

[Alec]

I agree. It seems the direction of interest is in some type of dual feed combo using one best focal point. I believe many at this point have both a 421 and a .03, would be great to use them instead of continuing to buy more, or a high $ combo.

 

[CharredPC]

I'll pay decently for a single well-performing combo lnbf. Cost really isn't the issue, unless it was just totally outragous. Availability is. What Sadoun described was a single LNB package with two F-connectors. Toss a Diseqc-mini on there, and you can use both C-band and Ku on the same dish at any point without going near your dish, with no sacrifice or signal loss due to offset multiple lnb configurations. It sounds ideal, and everyone trying this MicroBUD settup is hindered by having to run out and swap off lnb's depending on what they're watching or working on. Especially now, when we're getting into scalar ring designs that more and more push potential parrallel C and Ku lnb's further apart in dual setups, we need a single LNB for both. The only kind I can find available are full-sized BUD designs, often used, old, overly expensive, and with quite dismal noise figures. Maybe it's time to save up money and send Alec a sacrificial 421 to chop the back end off, and attach an Invacom into

 

[Shawn95GT]

Maybe it's time to save up money and send Alec a sacrificial 421 to chop the back end off, and attach an Invacom into

I was seriously making plans to take my cut-off wheel to my 'yet to be installed on anything' ASC421. I popped the 'bug cover' off so I could see down inside and at the back of the waveguide where we'd be hacking it off is a cast divider / bridge / whatever you want to call it. It appears to be perpendicular to 'straight up' on the LNB.

It seems to me that if you were to remove the feedhorn from a KU LNBF that this bridge would block a good chunk of the signal. I know my Ku LNBF it SUPER picky about things blocking it. I had my DSS LNBF sticking maybe 1/4" forward of the Ku one (hose clamped to the side of the Ku one) and I lost all quality on all sats! I slid it back so that the feedhorns were pretty much even and all was well again.

Borrowing from my experience with waveguide antennas (toying to long range wifi 'cantennas') I believe the back wall is needed for the C-band pickups to work right.

I very well could be and probably am wrong about this but I figured I'd throw that out there before someone takes the Sawz-all to the ASC421.

 

[caddata]

Shawn95GT:

The waveguide has to form a cavity with the end plate (it can't be open on the end). The septum, which would have to be removed, helps cancel any reflected waves. The end of the Ku feed you'd be adding likely would have something similar, however it may not.

There are several amateur radio web sites that discuss similar symmetrical multi feeds. They use similar frequencies and configurations. Zodiac's idea to offset both feeds either side of the standard focal point has got me to thinking that that may be the way to go. We're still tied to having to electronically switch between feeds either way we go.

I can't come to the decision to chop the back off my ASC421, but we won't know until someone does it.

Harold

 

[drhydro]

Posted 05-27-2005:


Any word on this? There's at least two or three threads discussing the best way to use both C-band and Ku on a single dish. I'm trying to come up with a way to use my Invacom 0.3dB and the offset C-band lnb together, and it always comes back to the same thing... there is only ONE focal point on a dish. You can stretch it a bit, deal with signal loss and work in parrallel, but the bottom line is that if you want to get the most out of your dish, use a single lnb at the prime focal location. In my opinion, the only thing lacking in our MicroBUD setups is dual band compatibility. And no, I don't count using archaic 10-12' prime focus BUD co-rotor

Anything? Anyone? (echo, ehco, echooo....)

Hi charred,
here is what i was told by mike kohl when i was thinking of using a c/ku lnbf last fall. I had seen c/ku lnbfs on fleebay and posted on this forum asking about them.

C/Ku combo LNBFs in one device fail miserably at isolation.
You will be sorry, because the first place reception will fall apart will be on Ku-band. Cal Amp tried perfecting one of these devices for years, and never succeeded. Now you have offshore made devices - for cheap - and you get what you pay for. As already stated in this thread, a C/Ku feedhorn with polarizer is the best for overall performance and isolation. (ADL RP-3 or
Astrotel PM-93 are suggested).

 

[zodiak]

That's exactly what I meant to say...

I'm definitely not a trained expert in high-frequency radio wave design but my basic understanding is that performance of such devices is extremely dependent on their shape, which, in turn, depends on the wave length.

This makes designing something that works over wider spectum more challenging and there is no way you can avoid compromises.

Multi-band multifeed, is just another way to make such compromises. The biggest advantages are that it's non-destructive and doesn't require fancy tools and machinery (and also can tolerate reasonable level of experimenter's ignorance ).

Besides, just by varying pretty much single parameter (that is angle displacement) you can either optimize for one band, or the other or anything in between! And if you are real perfectionist get a linear servo motor and motorize it! :shocked

 

[CharredPC]

drhydro:

That's understood. Which is why I asked about Sadoun's claim on a newly designed C/Ku lnb. You must admit that everything listed in your post is rather old technology. I was hoping for bypassing the polarizor idea and get something fully compatable with today's standard FTA equipment. I'm sure there'll be limitations and the Ku side won't be perfectly up to 0.3 Invacom snuff. But... SOMEthing!

 

[drhydro]

I have to agree with you charredpc, i would rather bypass the polarotor myself, it really limits my choice in recievers (pretty much down to 1 reciever). And there is always the chance that the servo will let go on a nice chilly winter night.

I am using a first gen. corotor and i am getting very good KU reception with it, much better than i thought i would on my mesh dish. Of course you could always go with the chapparal quad lnb feedhorn, but you might break the bank when it comes to buying all the LNBs ;-)

 

[Sadoun]

drhydro:

That's understood. Which is why I asked about Sadoun's claim on a newly designed C/Ku lnb. You must admit that everything listed in your post is rather old technology. I was hoping for bypassing the polarizor idea and get something fully compatable with today's standard FTA equipment. I'm sure there'll be limitations and the Ku side won't be perfectly up to 0.3 Invacom snuff. But... SOMEthing!

CharedPC

The C/KU combined LNBF we are considering is not yet optimized for offset dishes. I need some feedback from you guys who are testing the 120CM dish with a c-band lnbf on the best performing setup you have so far. This feedback will help in optimizing the performance of the LNBF.

The C/KU LNBF will have 2x F-connector outputs (one for C band and one for KU Band). A DiSEqC switch will be required to switch between the two bands. Polarity is voltage controlled. No polarizor is required.

 

[CharredPC]

The C/KU combined LNBF we are considering is not yet optimized for offset dishes. I need some feedback from you guys who are testing the 120CM dish with a c-band lnbf on the best performing setup you have so far. This feedback will help in optimizing the performance of the LNBF.

The only real factors in MicroBUD theory we've been working at using offset dishes are proper focal point, scalar ring design/placement, and dish size.

-The focal point really depends on dish shape/size. Some dishes have the proper focal point already set quite well using the default lnb position on the support arm(s). Others require some fine tuning, especially the more oval DirePC or Primestar dishes.

-Scalar rings have shown to help stablize signals by blotting out ground RF. Apparently, ones made for offset dishes (ie, "DEVO hats") work better than flat "normal" ring designs... big suprise. It also really hurts the signal to not have one at all... again, big suprise.

-Dish size, like everything else, makes all the difference in the world. I've recently been told of a 1.5m dish coming soon that's lightweight enough for a standard H-H motor. I know that's on my list of got-to-have's; in the meantime, 120cm works best. Anything smaller has some results, but it looks like everyone's agreeing 120cm is kind of MicroBUD 'standard.'

Looking at other company's official 'offset lnb' designs, they sometimes include a teflon wedge, and usually include the Devo hat design scalar rings. What kind of "feedback" are you looking for from us?

 

[Cascade]

I was just sent these pics which may be of interest.

 

[Alec]

Ku adapter

Cascade, great photos, did the person have any comments about Ku performance? This adapter would work fine on my 170cm dish. Caddata posted some photos of a dish using a reflector with Ku lnb mounted in reverse. Ive been wondering if a dual reflector would work for the off-set dishs , using both the 421 and .03 ? Attached is a sketch of what Im thinking. Would be a very inexpensive fix for persons having both a 421 and .03 with off set dish.

 

[Cascade]

All I got were the pictures in an anon email, no more info, sorry

 

[Alec]

Been thinking a bit, the dual reflecter, at best, wouldnt work any better than a side by side lnb config. A single pivoting reflecter with electric solenoid may work.

 

[caddata]

Man, there are so many ideas going around here, it has got me to thinking radical. I'm giving deep thought to the splash feed that has the Ku looking back into the throat of the C feedhorn.

I made my own TVRO dish in the early 80's. It was 15 ft. in diameter and worked well for three years until a hail storm trashed it. By that time, a local company had started to manufacture fiberglass dishes and I got one of their seconds for free just to haul it off. A can of bondo, lots of sanding, and a little paint and it worked for five years until I found a Birdview 8 ft. perforated with a HH mount that someone didn't want and that lasted until I moved to Florida five years ago.

My old system was sweet. A Uniden receiver and a Chaparral Corotor II with CalAmp lnb's. Left it with the home and have been without satellite TV until about two months ago.

HOA here won't allow big dishes so I slipped a Fortec 90cm up on the roof behind the chimney. I'm now giving deep consideration on replacing it with a fabricated, lightweight 48" prime focus dish that will be hidden from sight.

Check out my conceptual drawing in the attached image and give me your thoughts.

Harold

 

[Alec]

Caddata, your artwork is great. Id like to learn more about your ideas of the Ku feed. Ku lnb should have should have cone , flat scaler or just straight wave guide ? Your suggesting adding a home built cone to lnb ? I rounded up some materials today, tomorrow should be somewhat clear, badly want to have a shot at this concept myself.

 

[caddata]

Alec:

The attached image was generated in Autocad and exported in jpeg format. The image is one of the views of my initial layout. I've generated the parabolic curve and detailed my connections. I plan to use aluminum extrusions that are normally used as structural members of glass roofed sunrooms.

The idea of the feed is adapted from the photos attached to the first message of this thread. The Ku lnb in the photo was flanged but most of us will have the universal style with a plastic lense. My idea is to fabricate a fiberglass section that will mate with the C band scalar and transition into a metal (either sheetmetal or screen wire) cone that will accept the Ku lnb, which will be secured with a hose clamp. There will be a slight mismatch into the Ku lnb because it's geometry is for an offset feed but I don't think it will degrade the signal very much. The 48" dish will have much more gain at Ku frequencies than is required.

The portion mating to the scalar will need to be fiberglass or plastic to allow the reflected microwave signal to reach the focal point. This is similar to a "splasher" feed used by ham radio buffs who experiment with the 12Ghz. band.

I originally was trying to use a cassegrain feed but discovered that the subreflector was going to be way too large and block a significant portion of the dish. This layout blocks no more that the diameter of the scalar.

I think this is a design that can be easily fabricated because it's only 48" in dia. Forming the members to fit the parabolic curve will require a 1/16" tolerance. The perimeter, which will be the hardest to fabricate, will be a piece of aluminum angle that will be roll formed into a 48" dia. circle. I plan to construct the bending templates from 2X lumber and use a hard rubber wheel attached to a fulcrum to roll the components to the desired profiles

I'm trying to finalize my design and details so I can begin fabrication.

Harold

 

[Alec]

Im back at the lathe again, but wanted to check your ideas on Ku feed. The Invacom .03 has a 2.29 degree tapper to the wave guide. I have a piece of aluminum tube, will machine tapper for true fit. My concern is if I should use .03 as is or bypass .03 cone by adding straight wave guide. Ive never found out if the "black cone" has a reflective surface inside it. I think you can build your dish, I was going to try to build my own untill I found my 170cm in a scrap bin. Thanks

 

[Alec]

reverse feed

Well I took a shot at it. Tried .03 by itself looking back at 421........ 0 ! Then tried .03 with straight wave guide...... 0 ! Tried many settings with .03. The "black cone" is hiding a secret. The settup didnt seem to lessen quality w/421, just didnt do anything for the Ku.