Using microwave communications dish for Ku?

[Inno]

I have obtained (through legitimate means) an approximately 3.5' Andrew microwave antenna which used to reside on a tower to provide point to point communications for a remote community. It still has the feedhorn in tact although it used a waveguide to feed the signal from the equipment in the office to the antenna. I presume I already know the answer to this, but thought it best to ask anyway...Would the focal distance be the same for any LNB I place on it as the original feed? I figure it should be so that makes my work a little easier when it comes to fabricating a mount for the LNB.

 

[comfortably_numb]

Like this?

 

[Inno]

Not quite like that, but similar. I believe this one had a "radome" on it prior to being disassembled. I will post some pictures when I get to it. Just had some time to kill at work and figured I'd pose the question. It's getting to that time of year when I think about thinking about moving indoors and what needs to be done before that happens.

 

[LocutusOfBorg]

Last time I checked, that antenna does not have a downconverter in the feedhorn like an LNBF and requires either rectangular or elliptical waveguide to bring the signal into the building. That feedhorn you see in that photo is a rectangular feedhorn that is built for a specific frequency range and may have a tunable section or what is called "dent tuned". I suppose you could modify the feed system so that you could mount a feed support (buttonhook or struts) to accomodate a LNBF. Also, when you remove the existing feed system, you'll need to put a center plate over the hole in the center of the dish.

 

[Inno]

Correct that there would be no downconverter etc. I had planned to fabricate a mount for a LNBF.

 

[LocutusOfBorg]

Looks like that antenna may have been used for 18 GHz. But I'm guessing by the way the feed looks. Anyway, if you fabricate a support it should work for Ku. f/d and focal length can be calculated if you don't have the antenna specs.

 

[Titanium]

Remember to chose the correct LNBF to match the reflector's FD ratio. If .5 or higher, use a regular LNBF. If .3/.4 use a prime focus type LNBF. Using the wrong type LNBF will either under illuminate or overshoot the reflector surface.