Ku lnbf on C band feed.

[zamar23]

Thanks.

If I want to build a mini BUD from 1.2 m offset solid dish, and keep Invacom QPH-031 at its original focal point, where would I need to mount a C-band LNB like this one or similar to get both C-and-Ku band out of this dish? What would be the C-band LNB's optimal theoretical position in this scenario, and how it would depend on its specs? Could you mark both LNB positions on 2 dish section views (diagrams): vertical and horizontal?

What would be the best recommended C-band LNB make and model for this? Which 1.2 m offset dish make and model would work better: GeosatPro or Fortec Star, and why?

Will a combo C/Ku LNBF be a better choice instead of these two LNBs? Where it should be mounted?

 

[Mr Tony]

me personally would use the Invacom as is and add the 2nd (C-Band) LNB to the side. I tried using a combo unit (C/KU) on the 4 footer and KU Band for lack of a better term sucked. Signals really low

 

[pendragon]

Which 1.2 m offset dish make and model would work better: GeosatPro or Fortec Star, and why?

I'd give the edge to the Geo as it has a f/D of 0.5 vs. 0.6 for the Fortec. That's a lot closer to what a C-band feed can do; you can probably avoid a conical scalar.

Will a combo C/Ku LNBF be a better choice instead of these two LNBs? Where it should be mounted?

All things being equal a combo unit at the focal point should do better than having one feed off-axis. But as Iceberg said, it can also suck. It's hard to get both parts of a combo matched to a f/D so far from its design range.

A dual ortho might be a decent match as the Ku part of those feeds tends to have a narrow beamwidth. Then all you would have left is to inset the horn mouth into the C-band scalar rings. But it's an expensive experiment if you don't have a BUD to drop it on in case it doesn't work out.

If you want both C and Ku from a mini-BUD, you're going to have losses somewhere, which you can ill afford on the C-band side. My suggestion would be to put a single ortho on-axis and mill out a hole in the scalar for your Invacom. A single ortho with good LNBs has about the lowest loss one can get. But I have not and never will bother with a C-band mini-BUD, so take my suggestions with a grain of salt.

 

[dwingel]

I got my 3X1 scaler ring for my 10 foot BUD from Flavio Pairol in Brazil about three years ago. Came with Zinwell C, Ku, and DSS LNBFs. His e-mail is

pairol@vol.com.br

 

[zamar23]

My suggestion would be to put a single ortho on-axis and mill out a hole in the scalar for your Invacom. A single ortho with good LNBs has about the lowest loss one can get.

By "axis" do you mean the line on your schematics, dividing Ku-band offset dish by 2 equal angles, and passing through Ku-band LNB "by design" focal point? Can you give a link to a single ortho (with LNB) you recommend - I can't seem to figure out, how 2 different LNBs (C and Ku) will be mounted along the same axis.

 

[pendragon]

By "axis" do you mean the line on your schematics, dividing Ku-band offset dish by 2 equal angles, and passing through Ku-band LNB "by design" focal point? Can you give a link to a single ortho (with LNB) you recommend - I can't seem to figure out, how 2 different LNBs (C and Ku) will be mounted along the same axis.

I would put the single ortho (C-band only) feed on the dish's intended LNBF holder somehow, and have it centered. This will give C-band the maximum gain. That's what I meant by on-axis. I would then cut a hole for the Ku LNBF in the C-band scalar rings so the Ku mouth is as close as possible to the C-band mouth. That way the Ku feed is the minimum offset with respect to the antenna's mainbeam. The Ku feed will have some loss, but it can probably tolerate this better than the C feed.

As to which feed, the Chaparral single ortho is around $65. You would need two LNBs on top of this. There is a slightly different ADL single ortho for around $100. Performance-wise they're very similar. Much less loss than just about anything else.

You could wait for my dual ortho Frankenstein design to flesh out because that gets both C and Ku on axis. But a dual ortho costs around $200 minimum and your existing Invacom won't work.

 

[zamar23]

My suggestion would be to put a single ortho on-axis and mill out a hole in the scalar for your Invacom. A single ortho with good LNBs has about the lowest loss one can get. But I have not and never will bother with a C-band mini-BUD, so take my suggestions with a grain of salt.

Are you talking about the kind of mini-BUD setup, DREAMFOX1 tested, but an inverted one, with C-band LNB on axis? Can it improve the signal, if Invacom LNB is mounted in the same vertical plan as a C-band LNB instead of aside? It would have to be turned upside down for that, if mounted on top of C-band LNB - will it affect Invacom's polarity settings? Will it make any difference, if Invacom is mounted on top or below C-band LNB, if its pointed respectively down or up towards the dish center after that?


By the same token, if I put Invacom on axis, and add a C-band LNB on top of it, mounting both in the same vertical plan, passing through the dish center, and inclining C-band LNB a bit down towards the dish center - will it result in any C-band signal losses? I'd need to turn C-band feedhorn 90 deg. to make such mounting possible, but I assume, C-band LNB polarization can be manually adjusted after that? How their polarization is typically adjusted anyway?


Can you suggest the best C-band Circular & Linear LNB make and model for a Single Ortho Chaparral feedhorn mounted in an on-axis focal point of a 1.2 m ofset solid dish? What old or new 1.2 m offset dish make and model is best suited for C / Ku-band mini-BUD setup?

What is the physics behind flat and conical scalar rings? Why they're different in performance? Why they consist of several rings - how it works to amplify signal? How to select a proper Diameter & Size of a scalar ring? If there's a hole drilled on a side of scalar ring to accomodate a second LNB, how it theoretically affects the ring performance?

 

[pendragon]

Are you talking about the kind of mini-BUD setup, DREAMFOX1 tested, but an inverted one, with C-band LNB on axis?

Yes, that will ensure C-band gets the most gain, which is what you need with a mini-BUD.

Can it improve the signal, if Invacom LNB is mounted in the same vertical plan as a C-band LNB instead of aside?

No, because this will cause the LNBF to see above or below the Clarke belt. You will get terrible results.

By the same token, if I put Invacom on axis, and add a C-band LNB on top of it, mounting both in the same vertical plan, passing through the dish center, and inclining C-band LNB a bit down towards the dish center - will it result in any C-band signal losses? I'd need to turn C-band feedhorn 90 deg. to make such mounting possible, but I assume, C-band LNB polarization can be manually adjusted after that? How their polarization is typically adjusted anyway?

C-band polarization is adjusted by rotating the feed in the fixed scalar ring.

Can you suggest the best C-band Circular & Linear LNB make and model for a Single Ortho Chaparral feedhorn mounted in an on-axis focal point of a 1.2 m ofset solid dish?

First, the feed determines whether the LNB receives circular or linear, not the LNB. Second, I would suggest focusing only on linear C-band for a mini-BUD at least to begin with. There is very little circular C-band available in North America, and unless you use a wideband corotor, you will need separate linear and circular feeds. With either option you will have losses.

If you want close to the best LNBs, get a couple of Norsat 8115 LNBs. They're about $100 apiece. Norsat also makes slightly lower grade LNBs that would probably work nearly as well. The main difference is frequency stability, which isn't a big deal for FTA because most receivers have a broad capture range. You could also pick up a couple of generic C-band LNBs with decent specs for a lot less. That starts to become a gamble.

What is the physics behind flat and conical scalar rings? Why they're different in performance? Why they consist of several rings - how it works to amplify signal? How to select a proper Diameter & Size of a scalar ring?

Any scalar ring has a rather complicated effect on reception. For our purposes we will assume the primary effect is defining the look angle of the feed to the dish. A conical scalar has fundamentally the same purpose as a flat scalar, only it has a much narrower look angle. One issue with conical scalars is they are not particularly adjustable in terms of a look angle. If you have an offset dish with a low f/D, a flat scalar could very well turn out to be a better match. As C-band feeds tend to come with flat scalars there's little harm in starting there. You could always pick up a conical later if the flat didn't work out.

I hate to tread much beyond this point because we quickly get into theory, graphs and a background information not appropriate to this type of forum. However I will say that scalars do not amplify signals. The rings are intended to trap non-desired signals and noise coming from the wrong directions.

If there's a hole drilled on a side of scalar ring to accomodate a second LNB, how it theoretically affects the ring performance?

It won't help the C-band performance, but the degradation will probably not be too serious. When you want more than one polarization in one band, you have to accept compromises and losses. One alternative is a dual ortho, but there are losses there, too.

 

[zamar23]

Pendragon - thanks a lot for your feedback.

When mounted aside the C-band feedhorn on a mini-BUD, should Invacom Ku-band LNB be directed towards the dish center or looking straight?

If mounted aside slightly higher or lower than a C-band feedhorn (to compensate for reported by some testers slight vertical dish misalignment btw C and K signals), should Ku-lnb be directed a bit downwards or respectively upwards, or just looking straight?

Can a Linear V/H Ku-band LNB be mounted aside C-band LNB upside down in a motorized mini-BUD setup with feedhorn coax ports looking up for closer packaging of both LNBs, as sometimes done in multifeed stationary systems? How it will affect its polarity, when turning the dish?

What old and new 1.2 dish makes and models are known to work best for a mini-BUD?

I ask these questions, because some testers reported there results and system pictures, giving no analysis if their setup was the best under the circumstances, or can be significantly improved by following known guidelines. Adding more understanding about physical background on how components work together, and why performance may vary, allows to limit hit-and-miss trials to a reasonable time & cost amount.

 

[pendragon]

When mounted aside the C-band feedhorn on a mini-BUD, should Invacom Ku-band LNB be directed towards the dish center or looking straight?

Point it where the on-axis feed points. A bigger issue is making sure you have all the right distances mapped out. If you have enough adjustment range built-in to your design, that should be fine. Otherwise I would find this point by trial-and-error beforehand before committing to a mounting scheme.

If mounted aside slightly higher or lower than a C-band feedhorn (to compensate for reported by some testers slight vertical dish misalignment btw C and K signals), should Ku-lnb be directed a bit downwards or respectively upwards, or just looking straight?

I'm not swallowing the explanations easily. What is critical is getting the off-axis feed in the correct 'off-axis focal point'. A parabolic dish has only one true focal point, but off-axis signals will focus to some degree, albeit with coma. You are trying to find the tightest spot your feed can sample. On a prime-focus dish this would be strictly to one side or the other, but not up or down (I'm assuming the dish is motorized on a polar axis). On an offset this is a little messier because the feed is not going to see a circular dish at all when it is off-axis, but I would expect that the best point would not have much vertical displacement. Again, I'm assuming a motorized dish on a polar mount; many multifeed offset dish setups are fixed with the dish's long axis vertical. In this latter case one will have significant vertical displacements in the LNB positions.

Can a Linear V/H Ku-band LNB be mounted aside C-band LNB upside down in a motorized mini-BUD setup with feedhorn coax ports looking up for closer packaging of both LNBs, as sometimes done in multifeed stationary systems? How it will affect its polarity, when turning the dish?

Yes to the first question, but I would make sure there isn't a water drainage issue. If the dish is motorized on a polar axis, you'll be fine on the polarity.

What old and new 1.2 dish makes and models are known to work best for a mini-BUD?

All things being equal, I would take the one with the lowest f/D.

 

[zamar23]

Pendragon

Thanks very much for your continuous input!

 

[PopcornNMore]

I tried doing this on my 1.2m dish several weeks ago.

1) I couldn't get a strong enough signal having the C-band LNBF off to the side of the KU LNBF. Only picked up a few hot signals such as the religious channels.
2) The weight of the C-band LNBF pulled the KU LNBF slightly out of alignment causing reduced KU signal strength.

I want to try this again someday soon.

 

[zamar23]

A bigger issue is making sure you have all the right distances mapped out. If you have enough adjustment range built-in to your design, that should be fine. Otherwise I would find this point by trial-and-error beforehand before committing to a mounting scheme.

Anyone can suggest a bracket on the market or a known solution, which would allow to mount an Invacom Quad LNB aside of an offset dish focal point mounted C-band LNB such a way that provides for deep focal point adjustment for the Invacom (and extra Ku LNBs if mounted on the same bracket)? The adjustable brackets I looked at don't seems to allow that. Any suggestion on how to mod such a bracket using available components in stiff nice looking manner?

 

[zamar23]

It sounds like these RU brackets on pics below may be a good stuff for the task at hand to consider. A lot of interesting equipment at SatPro site, including whole bunch of C/Ku LNBs, Feedhorns and Rings. I wonder however, if moving Invacom back from the opening hand made in a C-band Feedhorn Ring would abstract from the Invacom LNB some share of signal reflected from the dish surface, and is there a way to avoid it - may be an extra Conical Ring for Invacom Quad will do?