KU Polarizer/Adapter for C Band feedhorn.

[caddata]

Alec:

You're going to have to fabricate some kind of conical adapter. The "splasher" doesn't reflect a pin point focal point back. It's more the size of a softball or larger. I would think that the large end of the cone would have to be more the diameter of the scalar and the smaller end be slightly larger than the o.d. of your Ku feed.

Remember to leave a large gap (6" +) between the large end of the cone and the face of the scalar rings.

I believe dissection of the adapter that started this thread would reveal a foil liner inside the cone section. However, the plastic could be mad reflective with the addition of powdered metal. Fiberglass was made reflective with the addition of carbon to the moulding mixture.

The angle formed by the conical section could also be critical, although 45 degrees would be a good starting point.

Don't give up, keep trying.

Harold

 

[pro96]

I was just sent these pics which may be of interest.

All I got were the pictures in an anon email, no more info, sorry

I know who this guy is, and he has posted your pictures plus the ones I have attached here. Here are his C-BAND/KU results using a 6ft BUD and the Ku Polarizer with An Invacom SNF-031 and a C-Band LNBF Dual Polarity 13-Degree LNB

He's getting a very nice C-Band signal from Satmex5 at 116.8w with a 6 footer

 

[pro96]

I actually purchased one of those from that same seller. I think he sells those pretty regular on ebay. he seems to be a pretty good guy. I purchased one, but he sent me 2 by mistake. When I contacted him he said to just keep the second one. I've never actully tried using it yet but I'm sure they probably work. How well they work and whether they degrade the signal or not however is perhaps the question. Anyway, if you note they have a polar servo to control polarity and accept a WR-75 flange LNB. So, if you use one of these, in it's original configuration you'll need to purchase a WR-75 Ku LNB and you'll need some way to control the polar servo. Some FTA recievers, like the Pansat 2500, will control a polar servo and have connections to hook it up to the reciever, but many FTA recievers do not. So, this could be an issue for some. There is however a workaround. If you notice the polar servo attaches to the device at what appears to be a C120 flange. Therefore you could simply remove the polar servo and attach a C120 LNB that supports 13/18v polarity switching.

Read your PM pal.

 

[Alec]

I had suspected that the cone may have a reflective surface. I have a large plastic funnel I can line with aluminum tape. pro 96, that guys getting a darn good Ku signal !!

 

[pro96]

I had suspected that the cone may have a reflective surface. I have a large plastic funnel I can line with aluminum tape. pro 96, that guys getting a darn good Ku signal !!

And C-BAND aswell using a 6 footer. Specially on Satmex that is not a very strong satellite to begin with.

 

[caddata]

Alec:

The long waveguide you machined may be too small in diameter. It may need to be closer the 40mm round wave guide on most of the universal lnb's. I believe your is less than a wavelength in diameter and It should be 1.5 of 2.

Harold

 

[Alec]

The entrance of the internal wave guide on the .03 is 15/16" . Another lub I have has an internal wave guide dia of 9/16". The outer rings on both vary in dia. The tube I found is slightly smaller than 15/16", just machined to tapper.

 

[Alec]

wave guide dia.

Caddata, attached is a photo of an Invacom C120 flange type lnb. Comparison of specs seems to closely match the tube dia I had inserted into my .03. Offer me your thoughts. Ive manage to be high bidder of one of the "black cones" on ebay. When I recieve it, I'll completely dissasemble it and resolve its construction. Thanksl

 

[caddata]

Alec:

Good reference work on the factory supplied drawing.

Most of the hams are using 1.5 times the free air wavelength for their circular waveguides and that would be 1.181" for the diameter. Microwaves react differently within the waveguide so I can understand that there might be some differences. I'm not sure how we can know for sure unless we experiment.

The problem with the Ebay part is that the Ku section is rectangular, so we will just have to see what happens with our experiments. My idea (if I can ever get the time to work on it) is to have the circular portion large enough to fit over my Fortec .4 lnb feed so I don't have to modify it and still rely on it's scalar section to cancel any out of phase signal. I expect to have a large number of out of phase signals with my homebrew dish.

Keep up the good work and keep us posted on your progress. This is getting really interesting.

Harold

 

[Alec]

The black cone has a straight wave guide tube with C120 flange, can be removed from square adapter and connected directly to Invacom C120 lnb.

 

[Alec]

more tests

Reffering to earlier photo Id posted of bypassing cone of .03, I tried same arangement with home built plastic cone lined with aluminum tape, .....0 quality. So, a bit tired of limited C band programing, I swapped back to Ku lnb. Out of interest, I tried short tube w/aluminum lined plastice cone on .03, equaled same as factory casted rings. Plastic cone had 45 deg sides, w/ 3.5" outer dia.. Then some time back Id built a flat scaler converter, but had 5 outer rings then, failed, removed 2 outer rings......quality slightly exceeded factory casted cone, which would be fitting since Im using a prime focus dish. After some failers, I was surprized that some simple home built experiments would show such good results. First pic, aluminum lined plastic cone, 2nd screen shot of results of same. 3rd pic of home built cone to flat scaler converter. Im no engineer, just that if the fish aint bitin, try another lure. Thanks

 

[Alec]

Ive read some time back about the use of dialectrics in lnb's. Late last night, came accross this site, states the use of a dialectric cone. Ive always wondered if the foam inside the "black cone" had an RF purpose rather than structural. http://www.elec.qmul.ac.uk/research/projects/dielcorrhorn.htmcom/

 

[Alec]

sorry, delete the " com/ " at end of link. http://www.elec.qmul.ac.uk/research/projects/dielcorrhorn.htm

 

[Shawn95GT]

sorry, delete the " com/ " at end of link. http://www.elec.qmul.ac.uk/research/projects/dielcorrhorn.htm

Thanks for the link. It is a good read and really explains a lot of what I was trying to understand when I asked what a scaler ring actually does. I wanted to know how vs what it does.

Shawn

 

[caddata]

Alex:

Good work, keep those experiments coming.

One series of experiments by a ham showed that a rectangular feedhorn worked almost as well as a scalar at 12 Ghz.

A styrofoam cup has been used many times to replace the "Bug Cover" on Corotor II feeds without causing signal loss at 4 Ghz. It appears they are using it to help attenuate unwanted waves on the referred website. That's the difference between 4 Ghz. and 12 Ghz.

Harold

 

[Alec]

Caddata, thanks. Im not an engineer, I have no real knowlege of mricowaves, offer your comments in a simplified form so that myself and others will understand better. You would usualy find me with heavy constructon equipment or heavy wrenches or welder, torches, etc. This microwave stuff realy eludes me. I am trying to understand it. Thanks

 

[Alec]

Ku polarizer/ C band adapter

I had recieved the "black cone" about 1 1/2 weeks ago. Health, a bit of employment and nearly constant rain lately have kept me from testing and disassembling it. The 1st photo is of my first trial of it, it seems to retard C band performace in order to capture or reflect Ku. A filter of sorts I guess, alowing some RF to pass, while some is reflected. The 2nd photo is of all pieces, black cone is simply a housing, foam is a means of spacing and keeping the reflector flat. 3rd photo is close up of reflector, in a 0 degree scew, straight up and down. 4th photo is of my later setup in order for a little more flexibility with Invacom. In most cases, reflector diminished C band quality by 20%, while Ku quality was (approx) 20% less than tests done solely by directing Invacom at dish. This reflector might work better with 8-12 dia dishes. My dish is only 170cm. For most persons, with smaller dishes, I think this would be a "thumbs down" device. Thanks, Alec

 

[kulakovich]

I have one installed w/ a Norsat ku lnb

It works great, if not as illustrated. I have it installed as per the instructions, and knowing nothing about nothing - Doesn't it position the LNB right in the top of one of the Ku sidelobes?

Strangely enough, I did try sawing the end off a Ku LNBf and positioning it all over the place, including bolting it to the adapter. No dice. The Norsat works great though.

kulakovich

 

[Alec]

kuladovich, the unit seems to work fine with strong Ku transponders, but weaker ones have not come in well for me. Ive tried many different settings as to focal point both C and Ku and scew. I can not say that my tests are acurate and might not reflect the results of the unit by any other persons. It just seems that my test results show some blockage of C band in order to gather and reflect Ku. The reflective membrain in the unit did a good job of drawing water up into the area do to the heavy rainfall in my area, but dissassembly and proper drying did improve signal but not as great as using Invacom by itself. The instructions did say to optimize C band quality first before istalling adapter, I did that, but most all C band signals dropped by 20%. I had found as much as 90% on RFD tv on G13 @ 127 deg, but after placement of adapter, sig went down to as little as 45. I can not neither encourage or discourage the use of this unit by any other persons. I have used a typical cone shapped Invacom, but bypassed cone with straight wave guide tube. I do not have the flange type Invacom. The locaton of entrance to wave guide does appear to be very specific. The use of the wave guide provided and the use of flange type Invacom could make the difference. My testing of bybassing usual cone type Invacom with straight wave guide and additions of cone or flat scaler converter has not resulted in any singnificant variances. If ths unit realy does so well, I would think it would be readily on the market. Alec