Im trying to make my own Ku/C Band Feedhorn but I am failing

[John Popper]

Inspired by what I saw on some other thread I cant find right now (I think it was made by "Paragon" who combined 4 C band feedhorns on his BUD) I tried to put to use one of the old chaparral C Band feedhorns I have lying around and add some Ku Band to it by using an universal ku lnb. Now my dish is a 10 footer and I have had success using this universal ku lnb (mainly used for offset plates) on my BUD by using a Ku on a C dish bracket like you can see in the following pic:

as it is right there in that pic I can get every channel @ 97, 101, 105, 94, 93, 85 and 83, which is about as good as im gonna get if I go by what the beams show for my area (near Mexico City, I get no beam for 87, 91, 99, 103).

Since I got fed up with the C/KU lnbfs that I bought and never worked (if interested you can check out my sad story here http://www.satelliteguys.us/c-band-...172-first-time-setting-up-coolsat-6000-a.html
and here: http://www.satelliteguys.us/free-air-fta-discussion/197532-whats-proper-dc-block-buy.html) and buoyed by the fact that I was getting a decent signal with this offset Ku LNB plus knowing that my C band chaparral works very well on the C band side I went ahead and tried to combine both thinking if I kept the ku band lnb close to the center and at pretty much the same length I might at least get something but unfortunately I have not been able to get any strength of signal yet on the Ku side, meanwhile the C band reception I get is pretty much the same as with the other untouched Chaparral Feedhorn I normally use, here is the final product:

before I even made this ghetto corotor I even tried positioning the ku band lnb above the chaparral and even below it, always keeping it in the center but same results no ku band.

I guess my question is am I completely wasting my time with this experiment? what suggestions can you all make so that I can at least get some ku band to complement my great c band experience without shelling out the big bucks for a corotor (which I probably will still end up buying)

http://www.satelliteguys.us/free-air-fta-discussion/197532-whats-proper-dc-block-buy.html

 

[Anole]

I read your post three times to see what you were actually asking.
I was distracted by the in-line pictures....

Are you saying you NEVER got any Ku on that BUD with the little Ku LNB, or just never got Ku when the Ku LNB was beside your C-band LNBF???
Did you move the dish a few degrees to recenter the Ku lnb on the satellite?

Another consideration is that you won't get great Ku signals with that LNBF on a BUD, because the F/D ratio is not optimal.
The LNBF expects about F/D=.7 (maybe .6), but the BUD provides F/D =.3 to .4
....meaning that your Ku LNBF is looking only at the center of the dish, not all of it.

I'd suggest you search our Gold Sponsors for something like this LNBF, designed for your exact need.
Alternately, look up the Invacom AF-120 feedhorn, and get a suitable LNB to mount to it.

 

[John Popper]

I read your post three times to see what you were actually asking.
I was distracted by the in-line pictures....

Are you saying you NEVER got any Ku on that BUD with the little Ku LNB, or just never got Ku when the Ku LNB was beside your C-band LNBF???
Did you move the dish a few degrees to recenter the Ku lnb on the satellite?

correct, never got ku when it was besides the chaparral and yes I moved the dish but nothing, seems that that particular ku lnb has to be EXACTLY at the center in order to work on my dish

Another consideration is that you won't get great Ku signals with that LNBF on a BUD, because the F/D ratio is not optimal.
The LNBF expects about F/D=.7 (maybe .6), but the BUD provides F/D =.3 to .4
....meaning that your Ku LNBF is looking only at the center of the dish, not all of it.

I'd suggest you search our Gold Sponsors for something like this LNBF, designed for your exact need.
Alternately, look up the Invacom AF-120 feedhorn, and get a suitable LNB to mount to it.

I kinda knew that going in but still was wondering if it was possible. Thanks for the suggestions, especially that geosat pro lnb for prime focus!

 

[John Popper]

the only question I have about that geosat lnb is how to mount it on my dish, would I need the bracket and hold it by it's "throat" like I do with lnb I posted in the first pic or does the ring come with holes

 

[SatelliteAV]

The GEOSATpro SL1P has a 40mm throat for mounting in a traditional LNBF clamp.

 

[phlatwound]

....Another consideration is that you won't get great Ku signals with that LNBF on a BUD, because the F/D ratio is not optimal.
The LNBF expects about F/D=.7 (maybe .6), but the BUD provides F/D =.3 to .4
....meaning that your Ku LNBF is looking only at the center of the dish, not all of it.

I'd suggest you search our Gold Sponsors for something like this LNBF, designed for your exact need....

I don't understand why that SL1P LNBF would work better on a prime focus dish, it's specs show it to be designed for a .5-.7 F/D?

Is it the little flat scalar, or......?

 

[Auric]

My expertise is very limited in this area, & I have never experimented with this, but on a C/Ku LNBF the Ku is 8"-10" past (higher) then the C part. Wouldn't you then need to move this farther away from the dish to get signal? Also I'm guessing this is just a fun project for you so keep up the good work. It's very interesting

 

[pendragon]

I'd go with the Invacom ADF-120 prime feed. It can be adjusted to match the f/D of almost any BUD. You can get a small variety of Invacom LNBs to attach to the flange on this feed, but some are hard to find and a bit pricey. Instead, the DN Superdish FSS 105 or 121 LNBs are very good, fit this flange and usually go for a song on eBay.

You might consider putting the Ku feed dead-center and offsetting the C-band side. Given that most BUDs don't focus well at Ku frequencies, this is probably your best bet. If you had a perfect dish, you would do a little better by offsetting both feeds from center by the same amount, but I would not suggest this for a mesh dish. Whatever you do, make sure that when the dish is exactly at true south, the centers of both feeds are on a horizontal line.

 

[Mr Tony]

I don't understand why that SL1P LNBF would work better on a prime focus dish, it's specs show it to be designed for a .5-.7 F/D?

Is it the little flat scalar, or......?

well it does work I tried 3 LNB's a while back with the 6 footer for a member

http://www.satelliteguys.us/1903812-post13.html
I have a 6 footer set up with it just in case I find a low quality feed that I really want to watch

 

[SatelliteAV]

In our comparison test between the GEOSATpro SL1P and the Invacom ADF-120 with matching SNF-031 LNB on a GEOSATpro 2.4M prime focus dish, the performance was nearly identical. What wasn't identical is the price tag..... $10

 

[pendragon]

In our comparison test between the GEOSATpro SL1P and the Invacom ADF-120 with matching SNF-031 LNB on a GEOSATpro 2.4M prime focus dish, the performance was nearly identical. What wasn't identical is the price tag..... $10

Brian, I know this wasn't intentional on your part, but one does have to question the validity of your test. As phlatwound points out, your website shows the f/D for the SL1P as 0.5-0.7. I don't know if that is correct, but that seems to fit typical offset dishes much better than FTA prime focus dishes. The GeosatPro 2.4m has a f/D of 0.46. This is on the VERY high side of prime focus dishes and not that different than some offsets. As a case in point the GeosatPro 1.2m has a f/D of 0.5 which is admittedly on the low side of Ku offsets.

Did you modify the ADF-120 before testing it on the 2.4m? If not this was very close to over-illuminating the dish if not actually so. Either way you may well have been compromising CNR for the ADF-120. The ADF-120 is specified for a f/D from 0.32-0.43. I have one and measured this to be about the maximum range of adjustment. I made some delicate mods to mine to get it to about a f/D of 0.5 to test on my GeosatPro 1.2m and that performed very well. But its real purpose is on dishes with much lower f/Ds.

Let's take a more typical prime focus f/D of say 0.35 on a 3m BUD. I'll be generous and give the SL1P a f/D of 0.5 vs. an ADF-120 adjusted to the correct f/D. The SL1P will only 'see' a 2.1m dish and will have a 3 dB loss in CNR vs. the ADF-120. Of course there are other factors including the LNB mounted on the ADF-120. But you can't fool Mother Nature if the SL1P has the f/D you're publishing.

 

[John Popper]

The GEOSATpro SL1P has a 40mm throat for mounting in a traditional LNBF clamp.

cool!

My expertise is very limited in this area, & I have never experimented with this, but on a C/Ku LNBF the Ku is 8"-10" past (higher) then the C part. Wouldn't you then need to move this farther away from the dish to get signal? Also I'm guessing this is just a fun project for you so keep up the good work. It's very interesting

yeah this is a fun little project, when I first began I tried to put the ku band lnb on top of the chaparral feedhorn using some long screws to place it exactly in the center but got nothing, I even tested it with a ku lnb from a bandstacked c/ku lnbf with the same results, got nothing

I'd go with the Invacom ADF-120 prime feed. It can be adjusted to match the f/D of almost any BUD. You can get a small variety of Invacom LNBs to attach to the flange on this feed, but some are hard to find and a bit pricey. Instead, the DN Superdish FSS 105 or 121 LNBs are very good, fit this flange and usually go for a song on eBay.

You might consider putting the Ku feed dead-center and offsetting the C-band side. Given that most BUDs don't focus well at Ku frequencies, this is probably your best bet. If you had a perfect dish, you would do a little better by offsetting both feeds from center by the same amount, but I would not suggest this for a mesh dish. Whatever you do, make sure that when the dish is exactly at true south, the centers of both feeds are on a horizontal line.

sorry pendragon I got your name wrong in the first post of this thread, and yeah this is probably what Im gonna try next, offsetting c band and placing the ku lnb dead center and we'll see how that goes, but first Im gonna buy that geosat lnb y'all are recommending

In our comparison test between the GEOSATpro SL1P and the Invacom ADF-120 with matching SNF-031 LNB on a GEOSATpro 2.4M prime focus dish, the performance was nearly identical. What wasn't identical is the price tag..... $10

thanks for the review! I know who Im gonna buy this from!

 

[SatelliteAV]

Pendragon,

Sorry, I should have noted that this info was just to compare two standard available items, optimized on a dish that was handy and for my own curiosity. More of a real world test rather than anything scientific or measured.

For the record...... The SL1P is considerably less expensive and performs very well!

JP,

Have you performed a string test on the dish to verify the parabola is not warped? The dish may be not accurately focusing the critical higher frequencies of KU, but is performing adequately for C-Band. Just a thought.....

 

[John Popper]

JP,

Have you performed a string test on the dish to verify the parabola is not warped? The dish may be not accurately focusing the critical higher frequencies of KU, but is performing adequately for C-Band. Just a thought.....

no I haven't but you know what I really don't want to change anything when it comes to the dish itself because c band is my main interest and I get c band about as good as i'm gonna get down here, ku band is just the icing on the cake. I will try that geosat lnb though!

 

[pendragon]

John - I initially wasn't paying attention, but your dish looks almost identical to one of mine, which I believe to be a 3.2m (10.5') Radyx. Do you have a depth measurement for it? My f/D calculates as 0.303, which is on the low side for a BUD. If your dish comes out the same, you will not have an easy time with Ku-band.

If the SL1P happens to have a nominal f/D of 0.6 (in the middle of its specified 0.5-0.7 range), you will suffer a 6 dB CNR loss because it will only illuminate the central part of your dish. Coupled with the surface imperfections of a mesh, you will be lucky to match the performance of a 1m offset dish. I wasn't expecting great Ku-band performance on my Radyx and only did a quick test after setting it up. To say it was only lousy would be a compliment. It doesn't hurt to try, but I don't want to raise any expectation that you're going to see much improvement. If I am wrong about my dish identification, then the above-described situation may not be as bleak.

 

[zamar23]

You will be lucky to match the performance of a 1m offset dish.

Is that so bad? With 1m offset dish one can catch just about everything NA wise in Ku-band at his location. Do I miss something in that comparison? Sounds strange JP, you're getting nothing at all.

 

[crackt]

Is that so bad? With 1m offset dish one can catch just about everything NA wise in Ku-band at his location. Do I miss something in that comparison? Sounds strange JP, you're getting nothing at all.

it may match a 1m offset dish if the BUD was precisely aimed. from a real world tester, aiming ku on a BUD just doesnt seem worth the effort. it is so sensitive that a breathe seems to drop signal significantly. id deifnately opt for a 1m offset unless its absolutely necessary to use a BUD for ku. it is fun to tinker tho. haha.

crackt out,.

 

[zamar23]

Its interesting, what's the physics behind mesh type dish reflecting sat signals? One would think they should go through the mesh... And why its more difficult to aim a C-dish in Ku-spectrum, why its more sensitive to aiming errors?

 

[1ADAM12]

Yes, well you did say you are getting pretty good Ku on that dish

The first picture shows a lnbf with a conical scalar ring for an offset dish. By using the Ku with a flat scalar ring for a PF you should pick up a point or two.

It looks like you should be using a six degree offset for you dish motor to move to the Ku lnbf. Are you doing that?

 

[SatelliteAV]

why its more difficult to aim a C-dish in Ku-spectrum, why its more sensitive to aiming errors?

Larger reflectors usually have a tighter beam.