Fitting an Octagon LNB to Channel Master dish

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G8DPH
Posts: 36
Joined: Fri Mar 01, 2013 4:44 pm

Fitting an Octagon LNB to Channel Master dish

Post by G8DPH » Tue Oct 16, 2018 8:16 pm

I have a 1.2m Channel Master dish.
Image

This has a feed horn suitable for a C120 flange LNB.
Image

What is the best way of mounting another type of LNB such as an Octagon?

Ashley
G8DPH
Ashley
G8DPH

g0mjw
Posts: 569
Joined: Sat Sep 20, 2014 9:15 am

Re: Fitting an Octagon LNB to Channel Master dish

Post by g0mjw » Tue Oct 16, 2018 9:05 pm

Cut off the front horn section of the LNB (carefully) and match it to the original C120 feed horn.

Take the LNB out of its plastic casing. It should look something like
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(image taken from the Amsat DL forum https://forum.amsat-dl.org/index.php?th ... reference/ )

Use a lathe or hacksaw to remove the LNB feedhorn leaving the short section of circular waveguide. You can then hopefully attach it to the C120 flange, or better a dual band 2.4 GHz / 10 GHz horn. I am wondering about doing the same thing myself.

You can just use the LNB as it is and adapt the mount, but it won't be as well matched to the dish. I don't know if that matters, it depends on your requirements.

Mike

G8DPH
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Joined: Fri Mar 01, 2013 4:44 pm

Re: Fitting an Octagon LNB to Channel Master dish

Post by G8DPH » Wed Oct 17, 2018 3:53 pm

Thanks for your reply.

btw I cannot get my pics to show. I've entered the url for my pics on Flickr but they don't show.
Ashley
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g4hiz
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Re: Fitting an Octagon LNB to Channel Master dish

Post by g4hiz » Sat Oct 20, 2018 5:42 am

Hi,

I had a similar problem with my old (but still good) Precision Antennas 1.2m prime focus dish. What I did was to reduce the diameter of the LNB housing from ~21.5mm to 20mm to fit the internal diameter of the antenna feed flange - which had the feedhorn on the other side. I used the edge of a 4mm file to reduce the LNB housing diameter a bit at first, before sawing off the feedhorn where it starts to taper. After sawing, I carefully reduced the diameter further to produce a close internal fit with the antenna feed flange. It was then super-glued into place. If you look into the feed, you will see a small step, but notwithstanding this, the antenna gain seemed to improve markedly compared to the previous bodged LNB fit.

73
Jen

2W0ODS
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Re: Fitting an Octagon LNB to Channel Master dish

Post by 2W0ODS » Sun Oct 28, 2018 12:37 am

The CM 1.2 doesn't really need a C120 flange for full illumination, the Octagon will fit and work perfectly fine in the standard LNB holder.
I've currently got a Inverto Black Ultra single in mine and on these dishes a C120 doesn't give you any benefit.
Both my CM and Gibertini have 40mm neck LNB's

I will have the "Goobay" PLL LNB in there over the next few days.
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g0mjw
Posts: 569
Joined: Sat Sep 20, 2014 9:15 am

Re: Fitting an Octagon LNB to Channel Master dish

Post by g0mjw » Sun Oct 28, 2018 8:22 am

They will, as long as held down by surfboards.

The horn that came with my 1.2m dish is a ridged horn like this:
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It was designed for the best G/T and to minimise sidelobes for that specific dish, giving even illumination right across the 10.7-12.75GHz (14.5GHz if it covers the uplink). These dishes were originally specified for VSATs and needed to meet strict performance criteria across the whole band.

The standard LNBs are a compromise, but not necessarily a large one, there is probably less than a dB between them. That is because the F/D of the 1.2m offset is similar to "standard" dishes. It is probably more important to put them at the correct focus position.

Which feed will work best at 10.4 GHz will need to be determined. It is out of band for both. Fortunately there are no satellites adjacent sharing the band so sidelobes will be less of an issue. I am concerned about intermods from the strong broadcast signals. These LNBs are expecting to be used with a 60cm dish and have upwards of 60dB of gain. A filter, if needed, is going to be easier to fit with a flange.

http://viasatelital.com/manuales/channe ... pe-123.pdf

PS. Still looking for a Channel Master 1.2m polar mount should anyone have one.

2W0ODS
Posts: 11
Joined: Sun Oct 21, 2018 5:15 pm

Re: Fitting an Octagon LNB to Channel Master dish

Post by 2W0ODS » Sun Oct 28, 2018 11:23 am

g0mjw wrote:
Sun Oct 28, 2018 8:22 am
They will, as long as held down by surfboards.

The horn that came with my 1.2m dish is a ridged horn like this:

Clipboard01.jpg

It was designed for the best G/T and to minimise sidelobes for that specific dish, giving even illumination right across the 10.7-12.75GHz (14.5GHz if it covers the uplink). These dishes were originally specified for VSATs and needed to meet strict performance criteria across the whole band.

The standard LNBs are a compromise, but not necessarily a large one, there is probably less than a dB between them. That is because the F/D of the 1.2m offset is similar to "standard" dishes. It is probably more important to put them at the correct focus position.

Which feed will work best at 10.4 GHz will need to be determined. It is out of band for both. Fortunately there are no satellites adjacent sharing the band so sidelobes will be less of an issue. I am concerned about intermods from the strong broadcast signals. These LNBs are expecting to be used with a 60cm dish and have upwards of 60dB of gain. A filter, if needed, is going to be easier to fit with a flange.

http://viasatelital.com/manuales/channe ... pe-123.pdf

PS. Still looking for a Channel Master 1.2m polar mount should anyone have one.
We have tried extensive testing the satellite community with that particular dish and there are no gains with a C120 horn, in fact its been detrimental in some cases, they might have been specified for VSAT but they weren't designed for that originally and its predominantly the 1m that was used for VSAT.
We have tried to squeeze every last drop out of that dish for getting weak signals.

One option is to use a custom made LNB mount, I talk to the person who makes these on another forum, I have attached a picture.
These are adjustable to get the LNB focused exactly in the right place.

Regarding the Polar mount, mine was in a sorry state and I completely restored it, the bearings are unobtanium but I have managed to find a source for bearings that fit perfectly and have better tolerances. I also changed every nut and bolt to stainless. If you do get a mount that has either no bearings (A few people removed them and used the polar mount fixed) or are worn I can help with that, I did a restoration thread here,https://www.satellites.co.uk/forums/thr ... on.173696/ it's worth registering if you haven't already done so as this is a dish enthusiast site and technical.

I spotted this on eBay: 232924701235 , This is an interesting mount as it's been adapted for incline as well, which would be quite useful for your intended purpose.

I'm currently working on a project as a motor controller using the ESP8266 which will interface with a VBOX or as a standalone motor controller to enable actuator control from a PC or any other device over Network or USB.
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