Gibertini feedhorn improving reception

[steffan_st]

Very interesting read here!
Learning a lot about this.

I found that SMW also makes feedhorn (which hitchcock already posted) that have f/d up to 0.65, anyone tried their horns? XM-601 or XM-351 C120

Also Chapparral have one but WR-75 f/d 0.6-0.9

Likvid: I might contact you later about the lnb but for now im going to experiment away when i get the dish up, with the gear i have.

I have tried the SMW xm-601 on the Gibertini,the result wasn't good at all.

 

[Likvid]

Chaparral is hard to get these days as they doesn't seem to be established on the market since many year and sells off old stock....

 

[steffan_st]

I have tried the SMW xm-601 on the Gibertini,the result wasn't good at all.

The XM-601 is meant for a dish with f/d 0.55.

 

[Likvid]

The XM-601 is meant for a dish with f/d 0.55.

Yes but i works within 0.45-0.65 so it doesn't matter.

 

[steffan_st]

Yes but i works within 0.45-0.65 so it doesn't matter.

Yes it matters,if you want an acceptable result with it the dish should have f/d very close to 0.55.

 

[steffan_st]

If you want to calculate f/d:s or feedhorn opening angles for different dishes this calculator is good:

hxxp://www.satellite-calculations.com/

Then click: "Offset Reflector Calculation"

 

[steffo78]

In the 80s when satellite-tv was still very expensive a lot of people made their own gear. In the library there is a swedish book which explains most of the work from receiver to lnc. This knowledge is not very important today as receivers and lnb is quite cheap. But the feedhorn is still interesting, at least I think so.
Maybe you should infact take a good horn and modify it until you got the right f/d?
Then you would have to know the exact focal-point and the with the help of a computer calculate a good horn. Or read a lot of books and calculate...
If you get the opening angle correct it would perform well.

I remember reading that book 10 years ago about the scalar rings and how they worked.
The horn itself is a widely used antenna, does not have the highest gain but the sidelobes are low thus making it good as a feed for a dish.
Radio-amateurs use horns on higher frequencys (GHz).

 

[steffo78]

Now this is interesting!

Have you compared at different freqencies?

There is 2 different Channel Master feedhorns,which one did you use for the installation?

Never believed the "Gibertini" feed should be very good,in my opinion it hasn't got enough relectors.

Now that I got the Gibertini feed I can confirm that is has 4 relector-rings.
I think that would be enough!?
And just as some described it, its not the finest tolerance.
The horn is one part and the other part is a pipe with the flange.
Where these 2 meet there is 0.5-1mm difference, the pipe is narrower than the horn connection (on one side) .
Since I have 2 I will try to "hone" one of them just like a clutch cylinder until I get a good surface.
Later I will try to put a extra relector on it, first I will have to find the focal-point.
Unfortunately I could not get a 150cm so I go for 120cm instead, no problem when I ordered but just when I was paying him he cancelled.
If anyone knows the exact focal-point on a 120cm Gibertini I would appreciate this information a lot!

 

[steffan_st]

Now that I got the Gibertini feed I can confirm that is has 4 relector-rings.
I think that would be enough!?
And just as some described it, its not the finest tolerance.
The horn is one part and the other part is a pipe with the flange.
Where these 2 meet there is 0.5-1mm difference, the pipe is narrower than the horn connection (on one side) .
Since I have 2 I will try to "hone" one of them just like a clutch cylinder until I get a good surface.
Later I will try to put a extra relector on it, first I will have to find the focal-point.
Unfortunately I could not get a 150cm so I go for 120cm instead, no problem when I ordered but just when I was paying him he cancelled.
If anyone knows the exact focal-point on a 120cm Gibertini I would appreciate this information a lot!

Sorry to hear about the feedhorn quality.


You will have no problem finding the focal point,just move the feed/lnb in and out in the holder until you get the strongest signal.

 

[dxsat]

Since I have 2 I will try to "hone" one of them just like a clutch cylinder until I get a good surface.
Later I will try to put a extra relector on it, first I will have to find the focal-point.
Unfortunately I could not get a 150cm so I go for 120cm instead, no problem when I ordered but just when I was paying him he cancelled.
If anyone knows the exact focal-point on a 120cm Gibertini I would appreciate this information a lot!

I tried filing out the inner part but it makes no difference. I also tried hammering it to get a vertical ellipse but this doesn't work either.
You'd be better taking a part- time job in order to afford a ChannelMaster feedhorn.
The correct focal point using the Gibertini feedhorn on this dish is with the horn pushed back as far as it will go, so the shoulder is touching the plastic adaptor rings. Any other position loses signal.

 

[TJExcalibur]

I wouldn't recommend that really as i had my Sharp 0.4 LNB die because of moisture getting inside the LNB.

I have spoken to some other people who had their LNBs die like mine when they modified it for C120.

And the difference are neglible between the LNBs, they perform the same, they just perform different in certain frequency bands.

I had moisture problems tripping my garden lights. I spoke to a sparky mate and he told me to pump in silicone sealant into an external junction when it had dried out. Worked a treat.

 

[steffo78]

You'd be better taking a part- time job in order to afford a ChannelMaster feedhorn.

Next summer I will be having beaversafaris again and taking good money from english and german tourists. So maybe I can afford one then! O-Ha

 

[steffan_st]

Steffo 78@

Have you measured the opening angle of your Gibertini feed?!?

 

[steffo78]

I am not sure how to measure it.
If I look at the angle of the scalar-rings its a lot smaller than 74 deg. which is the correct angle for f/d 0.66.
Around 45 deg, have to check more carefully.

 

[Channel Hopper]

You are not likely to get a correlation between feed aperture and efficiency against f/d ratio, especially on an offset dish .

Typical figures for professional antennas are however
0.6 f/d - 51 degrees
0.8 f/d - 39 degrees

though these are with far more extensive scalar rings