FOCAL LENGTH & SPACING RESOURCES?

[MikeinBaja]

Was cruising around the net looking for the focal length calculation - going to take a stab at fashioning a multi LNB setup - does this formula look right?

Diameter of dish X diameter of dish divided by Depth of dish X 16

Also, could not find a formula for LNB spacing for setting up for multi sat reception. Is this a standard formula or does it vary by location due to delineation?

Looking to learn more before I break out a grinder and welder (just kidding - will put all together with cable ties & duct tape first - then weld!).

Mike

 

[Anole]

However that focal length thing works, I'm pretty sure it's only applicable to prime feed dishes.
Don't see how you could apply it to the offset dishes we often find.

However, I did take a stab at F/D calculations in a Birdview thread.
The F/D is an indication of how wide a view the LNB needs to see the entire dish.

Also, could not find a formula for LNB spacing for setting up for multi sat reception. Is this a standard formula or does it vary by location due to delineation?

If you'd searched this forum for the question, you should have run across me often promoting the good works of one of our member:

MJflash and his math to put two LNBs on a single dish:
http://www.satelliteguys.us/free-air-fta-discussion/89049-offset-lnbs-theory-practice.html

It is based on the dish's focal length, and it does vary by where you are located in relation to the birds.
For a recent example, pages 4 & 5 of the AMC 21 thread is a good place to get your feet wet.
http://www.satelliteguys.us/free-air-fta-discussion/150263-amc-21-a-3.html

I think WescoPC got his spacing by measuring LNB location:
http://www.satelliteguys.us/free-air-fta-discussion/151258-building-1-2-meter-dish-2-spacing.html
An age-old, and perfectly practical solution to the problem!

 

[MikeinBaja]

Thanks, this is exactly what I was looking for. I did a search of this site first, but didn't get a hit on any that you referenced.

Thanks again for the links

 

[SatPhreak]

I've always done it the non scienticic way, hold a second lnb on the side that the other sat you want will come in on (if the sat is W of were the dish is aimed it will show up on the E of the main lnb) and move around till I get a signal. I then fab a bracket that will hold the lnb in the aproximate area, allowing room to fine tune it. Then I mount it and fine tune for best signal.

It works, but I don't have the best available tools at home to measure and make a bracket based on where it should be.

 

[MikeinBaja]

I've always done it the non scienticic way, hold a second lnb on the side that the other sat you want will come in on (if the sat is W of were the dish is aimed it will show up on the E of the main lnb) and move around till I get a signal. I then fab a bracket that will hold the lnb in the aproximate area, allowing room to fine tune it. Then I mount it and fine tune for best signal.

It works, but I don't have the best available tools at home to measure and make a bracket based on where it should be.

Been there, done that - and it sure does work. Plan was to get a calculation that would get me in the neighborhood, then build a spare parts temp bracket but surely will need duct tape & shims to determine final position. Figure I'll build a sturdier final after I know all the parameters from testing.

My "winterish" project.