Multi-Focus LNBF (C and Ku Band)

Discussions about low-noise blocks, waveguides, horns and other components used at the prime focus of your reflector dish.
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Multi-Focus LNBF (C and Ku Band)

Post by tek2000 » Wed Jul 23, 2014 11:19 pm

Here is an example of multi-focus feed for C and Ku Band reception that I prototyped for myself.

It consists of 4 LNBs:

1. The center C-Band LNB for linearly polarized (V/H) reception. The majority of C-Band signals available in North America are of this type, so it was placed at the prime focus for maximum gain.

2. 3 degree offset C-Band LNB for the reception of circularly polarized (R/L) signals. This is used for receiving satellites transmitting this type of polarization primarily to Central and South America. C-Band circularly polarized signals can be found on 18W, 20W, 22W, 27.5W, 34W, 40W, 47W and 53W. It is especially useful for 40W where there are hundreds of channels available (mostly Spanish). The 3 degrees offset results in approximately 1dB loss in C/N ratio, relative to prime-focus.

3. A Ku-Band LNB mounted 3-degrees off centre for the reception of linear (V/H) signals. This is used for the reception of FTA Ku-band signals commonly found on 30W, 50W (Claro TV), 72W, 83W, 85W, 87W, 93W, 95W, 97W, 99W, 101W, 103W, 107W, 113W, 121W, 123W, 125W (Claro TV). It can also receive Shaw transmissions from 107W and 111W if you have a digicipher tuner or subscribed Shaw receiver. Again, due to the 3 degree offset, there is a 1dB loss in C/N ratio, relative to prime-focus.

4. Last, but not least, a Ku-Band LNB was mounted 5 degrees off centre for the reception of circularly polarized (R/L) signals. This is primarily used for picking up signals broadcast by Dish, DirecTV and Bell at 61W, 72W, 77W, 82W, 91W, 101W, 103W, 110W, 119W and 129W. The loss due to the 5 degree offset is about 2dB relative to prime-focus, but hardly problematic since the broadcasters of these signals transmit more power and use lower FEC rates on average.


How does this setup work? It works remarkably well. The prototype is mounted on a 10ft mesh dish and 99.9% of all C and Ku band signals can be received reliably!

For those of you trying to receive C and Ku signals together using a combo LNBF, you will encounter 3 problems:

1. C-Band signal reception will be degraded by about 1-2dB due to reflections coming from the backend ku LNB.

2. Ku-signal reception will be degraded by 2-3dB due to the front-end C-band waveguide which acts as a kind of filter for Ku signals.

3. The optimal focal point for C-band signals will not be the same as ku signals primarily due to distortions in your dish surface geometry and/or poorly designed C/Ku combo LNBs. This will degrade signals by another 1dB.

Not to mention the fact that you have to insert/remove a dielectric plate for circular signals, which causes even more losses.

We can do better than that!

I am currently in the process of designing and manufacturing a feed system with a high-gain prime-focus C-Band LNB that can switch between linear and circular polarization without the need of a dielectric plate and an offset Ku LNB that can receive both linear and circular signals without the use of a dielectric plate. The ku LNB will be 2 degrees off-centre to minimize off-centre losses as much as possible.

This will be the ideal solution for those who have an 8ft or 10ft or 12ft mesh dish and want to receive all signal types. The cost of this feed system (including LNBs) will be under $100 USD.
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Multi-Focus LNB Feed
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Re: Multi-Focus LNBF (C and Ku Band)

Post by drury » Sat Jul 26, 2014 12:56 am

That is one mean looking setup tek!!!

I would love to have something like that capable of receiving every signal type...
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Re: Multi-Focus LNBF (C and Ku Band)

Post by mountainman » Wed Aug 13, 2014 7:42 pm

Always nice to see people thinking out-of-the-box. I've constructed something similar, but not as elaborate. ;)
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Re: Multi-Focus LNBF (C and Ku Band)

Post by tvroadmin » Wed Oct 29, 2014 2:27 am

There is now more technical information about off-axis feeds in our guides section.
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Re: Multi-Focus LNBF (C and Ku Band)

Post by buzzie » Wed Dec 03, 2014 5:21 pm

Nice set up tek2000. :coolsign
Was wondering if you can just go with a cu/ku lnb with a circular ku next to that. If that is not a good idea was wondering if you used 2 Scalar Ring for you set up and what kind of ku lnb's did you use and do you have them.Am getting into the big dish and looking at all the choices out there. Use the small dishes right now.Like the set up. Lots of choices for what satellite you want to watch.
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