How to find optimum vertical polarization.... 1

[boondox]

How can you find the optimum vertical polarization number for a Ku band antenna? Where is the best online resource to explain cross polarization and how to find the optimum polarization?

 

[VEBill]

Assuming that you're refering to a satellite antenna, and the satellite is using vertical and horizontal polarization (not R & L circular), then you need to rotate the LNBF to match the relative orientation of the satellite. Only if the satellite is exactly due south (for northern hemispherians) of you is the angle zero.

Most people simply peak it after everything else is lined up. Is everything else lined up yet?

Do you have a satellite finder (the beeping gadget that connects in line) ?

 

[VEBill]

Oh, and...

Cross Polarization is a method of reusing the same frequency spectrum by taking advantage of the ability of an antenna to null out the signal that come from an antenna that is oriented at 90 degrees (for H & V), or opposite circularity (R vs L).

It permits doubling the effective bandwidth.

It means that, for satellite TV, you get an effective 1000 MHz of bandwidth for every 500 MHz of frequency spectrum.

 

[VEBill]

Here is a link to a nice sat angle calculator:

http://www.sadoun.com/Sat/Installation/Satellite-Heading-Calculator.htm

 

[boondox]

Yes, everything else is lined up if you mean antenna pointing and equipment settings.

No, I don't have a satty finder but I do have a beacon receiver with an excellent signal strength (-62.7) and the rx light on my linkway modem is flashing which means I am receiving traffic.

So, for the cross pol thing would my assuming my tx is V pol at 10 meg then I could rx 10 meg from my d/e at the same freq if they were using H pol? Or would the change in pol from V to H occur at the satty?

Also, another tech informed me the best way to find the optimum pol was to rotate the LNB until the signal drops into the dirt on the spec anny, and then add 90 degrees to that number. Is this correct? It seems it would get the same results you described by a diffent method?

Another question. Suppose all my terminals were within 200 miles of each other. How far off would my pol numbers be if we're all using V or H to shoot to the distant end?

 

[VEBill]

I've figured out that you're not installing a TV dish... ;-)

You should be able to use almost exactly the same adjustment settings as someone else only 200 miles away (assuming all else being equal).

Polarization adjustments are a broad peak and a sharper null on the opposite polarity. Nulling out the opposite polarity may be more important than perfecting the broad peak. Why not do both, keep track of the numbers, and figure out the best adjustment. Assuming your equipment permits it, then it's a two minute exercise.

For satellite TV dishes (Ku-band FSS), the polarity peaking is the easiest part of the process.

If things aren't working, then there's a million other things to check other than the antenna...

Some (many?) satellites offset the tranponders (by a half-step of the transponder spacing) on the opposite polarities so that the channel isolation is maximized.

 

[Higgler]

You don't lose much when you're not perfectly aligned to vertical.
the loss is 20 * log (cos (error angle from perfection)).
Hence if you are errantly tilted 5 degrees, the cosine of 5 degrees is 0.996, 20*log 0.996 = 0.035 dB, not much loss.

kch