6 Foot dish for Ku

reho33 · #1 (**permalink**) 08-02-2006, 12:03 PM

Can a 6 foot prime focus dish be used for Ku? And if one were to do so, how would a person find the actual elevation settings for it as the settings given by most calculators only do it for offset dishes?. Lastly, would the adjustments be a lot more critical than a 3' dish? And how much more gain and adjacent satellite rejection would one expect?

elgemcdlf · #2 (**permalink**) 08-02-2006, 12:11 PM

Quote:

Originally Posted by reho33

Can a 6 foot prime focus dish be used for Ku? And if one were to do so, how would a person find the actual elevation settings for it as the settings given by most calculators only do it for offset dishes?. Lastly, would the adjustments be a lot more critical than a 3' dish? And how much more gain and adjacent satellite rejection would one expect?

The adjustments are still the same. Or I guess I should say same will get you at least close. As to more or less critical yes and no. Depends on what you are trying to receive but basically the larger the dish the larger the side lobes which can get rough to distinguish from the actual signal itself. Worth every bit of the install though as more surface makes for more signal trapped which makes for a better picture.

wejones · #3 (**permalink**) 08-02-2006, 01:26 PM

Quote:

Originally Posted by reho33

Can a 6 foot prime focus dish be used for Ku? And if one were to do so, how would a person find the actual elevation settings for it as the settings given by most calculators only do it for offset dishes?. Lastly, would the adjustments be a lot more critical than a 3' dish? And how much more gain and adjacent satellite rejection would one expect?

Yes, a 6 foot dish can be used for Ku. What Steve says about sidelobes is not so much a function of dish size, but dish quality, and I believe also the F/D ratio (I think high F/D dishes work better). I use a 10' dish, and I have bad sidelobes, which sometimes confuses things, however it works just fine most of the time. My current sidelobes are partially due to the quality of the dish, and partly because of the fact that I dropped the dish from 8' when I installed it, and due to the fact that I beat it with a broom every winter to knock snow and ice off, so it is all dented. My previous 10' dish had much less in the way of sidelobes, and worked very well on Ku. Basically, if you have a new relatively good quality dish, the sidelobes won't bother you, but if you're thinking buying a used dish that may have been abused, you might have a problem. My first of 3 10' dishes didn't work well at all on Ku, because it was an old 1980's era C-band dish, that wasn't shaped well, and had big mesh.
I also have a 6' dish, that originally worked well on Ku ( according to the guy I bought it from ), but it doesn't work worth a darn now, mainly because I left it out in the freezing rain over a couple winters, and the hollow ribs filled with water, froze, and split, which warped the thing badly.
So if you're buying a new dish, I think a 6' dish should be fine on Ku.

Now... for declination numbers, you could use my on line calculator, at:

http://wejones.ftdata.com/bjdishcalc2.htm

or go to my page, ie:

http://www.megalink.net/~wejones/inst&align.html

I have a program there that calculates Az/El and declination, etc.

However I really like to recommend :

http://www.geo-orbit.org/sizepgs/tuningp2.html

which is about the best web page out there for aligning TVRO systems.

Relative to elevation and declination, you can use the declination calculator at the Sadoun page, but it is calculating the elevations and declinations for a south facing satellite, which is OK for smaller dishes, but is not the declination you should be using for bigger dishes, which require more accurate tracking.
The Geo-orbit page above explains this, and has charts for both.

If your dish isn't motorized, but instead and Az/El, then you could just use the Az/El found at the Sadoun site, as they are the same for either offset or prime focus.

reho33 · #4 (**permalink**) 08-02-2006, 02:13 PM

Thanks Guys! Well explained. Having a lot of fun with my 36" dish. Some transponders only come in at 35-40%, even with tweaking, but still locked. My location does not make it friendly for a fixed position, will have to move the dish to another part of the property to get G10R, etc. In it's current position I can get 79 degrees to about 103 no problem. I was fixed on IA-5 for longest but got bored so switched to IA-6. CBS Newspath feeds, etc. And that wacky Dr. Gene Scott....

wejones · #5 (**permalink**) 08-02-2006, 02:17 PM

Quote:

Originally Posted by reho33

I was fixed on IA-5 for longest but got bored so switched to IA-6. CBS Newspath feeds, etc. And that wacky Dr. Gene Scott....

Plus IA-6 is usually a good place to pick up a bunch of NFL preseason games.

boroda1 · #6 (**permalink**) 08-02-2006, 02:30 PM

The day before yesterday I saw a news reporter on this sat, who actually was PREPARING to make his report. He was scratching himeself here and there, swearing at "f@#$ing bugs", killed one on his forehead, asked for his laptop,etc. There were passing cars, honking. Finally, he did a 30 sec. report, light went off, and signal quality on this channel momentarily dropped to "red zone". It was funny!