Precision, Threaded Feed-horns ???

[Achebee]

I am looking for a precision feedhorn, i.e one that has scalar ring threaded to the base for fine tuning the FD on a 12 ft. antenna.
I am using a Chaparral Corotor II C/KU but actually, this is a pretty funky setup.
The scalar ring housing has one allan screw situated way up front by the base, hard to get at, and just a mess to do any fine tuning... ONE CAN NOT CALL IT FINE TUNING...THIS IS JUST SEAT OF THE PANTS LUCK... PERIOD. I am actually surprised that I am receiving anything with this feed-horn.. I am looking for info anyone has and a decent review of good feed-horns C or KU and C/KU I read here looking around about feed-horns with the threaded scalar, but can't find a name or brand name that I can use to link to a source to buy something decent.
I am located 15 degrees north and need serious precision on all aspects of my antenna.. the Corotor would be fine in other areas, but it is a joke with the FD adjustment being such a mess to deal with... The Corotor works fine, but again with luck only.
thanks for your help, HB

 

[1captain]

I have used that feed horn in the past, an have not been that happy with it's performance on the Ku side, wile I have found that the co-rotor will out perform it.

an yes I know you're point about the chaparral scalar ring with it 1 alan set screw. a better scalar to use is a channel master off their old c-band feeds, they have 2 or 3--1/4"x20-bolts that hold the feed. a far better way to hold it perfectly centered. an know where you are coming from on the F/D ratio an percision, that is a very important part of dish tuning. what I used here to set the F/D ratio is a depth caliper, that a machinist will use to measure the dept of a hole.

I thought I had more pictures of the channel master scar rings but only this 1, an it doesn't show the back side with the 3 mounting bolts for the feed throat.

 

[Achebee]

Thanks for the info... this looks like a great option.
I am still interested in these threaded scalars I read about, I think one can keep it all centered properly that way.
I appreciate your help, and look forward to seeing if anyone else responds about the threaded setup, HB

 

[hd fan]

Man an I thought that I had a lack of a woman issue, you guys beat me , lol.

 

[Greg Mueller]

I've never been happy with the cast feedhorn setups either. As you say it's pretty hit and miss. The threaded idea is great.

Here's something I have done that helps a lot.....

You need a hose clamp big enough to go around the throat of the feedhorn.
3 or 4 dowels or set screws. I used hardened 1/4" dowel pins I had laying around.
I put one dowel pin at each of the locations that has the F/D ratio on the throat and held them with tape at my dishes F/D ratio (about .375) I measured the distance from the end of the throat with a caliper, to make sure they were all even.
Then I put the big hose clamp on and tighten it down to hold the dowel pins in place.

What that does is provide a base/feet to rotate the feedhorn on. If you make sure each dowel is touching when you screw in the set screw and it will not be cockeyed.

I mark a dot with a felt pin on the throat and one on the scalar ring and that gives me a reference point for rotational adjustment.



I plan to make a plate that will clamp onto the throat that will be a little more sophisticated for my future projects.

Obviously a threaded throat would be the cat's meow.

 

[starman345]

Greg, that is a good idea with the dowel pins and hose clamp:up I'm going to try that this spring when I do the seasonal re-aim.
If I'm understanding the threaded throat/scaler correctly won't it cause a conflict when you are trying to keep the skew(throat roatation) right and the f/D at the right point? If you screw the throat in or out of the scaler to get the proper f/d then the skew would change? Maybe if the threads were fine enough a close compromise could be made.

 

[Achebee]

Man an I thought that I had a lack of a woman issue, you guys beat me , lol.

Ha Ha..!! Looking for the perfect one, you know??? Flat head and no teeth...etc. etc..
Make a good ad in the personals... Looking for a gal with a threaded scalar ring...
Kill 2 birds with one stone.!!

 

[Achebee]

I've never been happy with the cast feedhorn setups either. As you say it's pretty hit and miss. The threaded idea is great.

Here's something I have done that helps a lot.....

You need a hose clamp big enough to go around the throat of the feedhorn.
3 or 4 dowels or set screws. I used hardened 1/4" dowel pins I had laying around.
I put one dowel pin at each of the locations that has the F/D ratio on the throat and held them with tape at my dishes F/D ratio (about .375) I measured the distance from the end of the throat with a caliper, to make sure they were all even.
Then I put the big hose clamp on and tighten it down to hold the dowel pins in place.

What that does is provide a base/feet to rotate the feedhorn on. If you make sure each dowel is touching when you screw in the set screw and it will not be cockeyed.

I mark a dot with a felt pin on the throat and one on the scalar ring and that gives me a reference point for rotational adjustment.



I plan to make a plate that will clamp onto the throat that will be a little more sophisticated for my future projects.

Obviously a threaded throat would be the cat's meow.

Greg, a good idea indeed.. that is exactly what is needed, a base/feet for the feed-horn to rotate on..I am going to fiddle with it this week and make that adaption...Very good suggestion..I like the idea of the dowels as you can just loosen the clamp a hair to free them up a bit, make the adjustments and all the points would stay equal.. or close enough, and re-check them with a caliper... thanks for the idea...I am going to dig deep in here and try and find the thread or article posted here that had the discussion about the threaded scalar, but this I believe will bail me out of trouble, and make the Corotor II a much better feed-horn.. thanks, HB

 

[hd fan]

Wouldn't the Corotor II select polarity by using a servo to rotate the feed?. In that case the threaded feed would not be a problem for skew, right?.

 

[Greg Mueller]

Greg, that is a good idea with the dowel pins and hose clamp:up I'm going to try that this spring when I do the seasonal re-aim.
If I'm understanding the threaded throat/scaler correctly won't it cause a conflict when you are trying to keep the skew(throat roatation) right and the f/D at the right point? If you screw the throat in or out of the scaler to get the proper f/d then the skew would change? Maybe if the threads were fine enough a close compromise could be made.

You'd have to make one complete revolution with a threaded throat to keep the same skew.
Those threads look pretty fine though. I bet that small of a change (one thread or part of one thread) wouldn't matter too much on the FD adjustment once you got close and wanted to change the skew.

 

[Greg Mueller]

Wouldn't the Corotor II select polarity by using a servo to rotate the feed?. In that case the threaded feed would not be a problem for skew, right?.

Yep, but it seems like sometimes I have gotten it adjusted so I run out of adjustment right at the end of the polarotor adjustment.

If you use a dual LNB C-Band feed horn (my future project) then there's no way other than rotating the feed horn to get the skew adjusted cause there's no polarotor