Polarity Problems

[ORF]

I am unable to receive V polarity at the East and West portion of the sweep of the sky on my 8' BUD. I receive both H and V at very good levels in the center of the arc (Galaxy 23 at 121 W). I doubt (or hope) I am not the only one to have had this problem, but I have no idea what I am doing wrong. I will be very grateful for any help.

Thanks,
Pat aka ORF

 

[FaT Air]

Nope. Don't think that is a common problem. Not one I've ever heard of anyway. Maybe, if we knew what you have your BUD outfitted with, feed wise, may help. Is the BUD on a polar mount? Receiver? More detailed info, all around, will get better informed answers.

 

[turbosat]

If he's using a polarotor feedhorn, it's not set up properly. I have had that trouble before too, but it doesn't bug me too much because I'm using an analog receiver to move the dish and set the skew, and my receiver has great memory for the skew setting for each satellite programmed in it. The trick is, go to due south satellite, fix feedhorn so the polarity motor box is lined up with the north/south axis, and it should be very close to correct. If its an lnbf he is using, that is another wrinkle but shouldn't be that much different than my old-school feedhorns.

 

[ORF]

Re: My polarity problem........
The BUD is polar mounted, using a BSC621 C/Ku LNBF. I have been only concerned with the C band for now and have not paid a great deal of attention to the performance in the Ku band (that's next on my agenda). I think I installed the BSC621 correctly, the instructions do seem to leave a little to be desired.
My receiver is a Pansat 4500.

Pat (ORF)

 

[Nosbod]

Move your dish to the top of the arc. On your LNB there will be markings something like 30-0-30 sort of in a half circle. Your have to adjust the LNB so the 0 is aligned in line with the top and bottom of the dish. It has to be centered in line with north/south on your dish
This should solve your problem if your dish alignment is correct.

 

[FaT Air]

One reason for the instructions being minimal is there is nothing cut and dried for all installations other than what is outlined in the instructions. Basically boils down to making sure it's centered and facing the exact center of the dish. Then it's adjust focal length and skew for max.(Tweaking the feed focal length is necessary as two dishes of the same make may actually focus a bit differently as there's assembly errors that can't be controlled.) For the problem your experiencing, I'd check everything that may be a source of it. I'd check the position of the probes in the throat of the feed. Confirm that they are 90° to each other. Then I'd adjust the focal length and skew on a sat that I do get both polarities. Then, I think I'd rotate the feed 90° so V would pick up H and H would pick up V. and compare the Q from normal to reversed and make sure both polarities are working equally. (then put it back to normal if that checks out) So we can compare, what satellites are you unable to "receive V polarity at the East and West" Is the dielectric plate installed? just thought I'd ask.(it shouldn't be for CONUS satellites)

 

[ORF]

Fellow FTA enthuseasts:
Sorry it has taken this long to get back to you, but I sincerely thank you for your help. I have to admit I wasn't real anxious to go through all the "set up" again, but I did. I now am receiving both Vertical and Horizontal transponders at both ends of the arc that I can "see" (135 W - AMC 10 to 91 W - Galaxy 17). Beyond those limits I am looking at tall fir and cedar trees. My next challenge is to improve the Ku band reception (it is extreeeeemly sharp and touchy). Thanks FaTAir, Turbosat and Nosbod for "pointing" me in the right direction.

 

[turbosat]

Good to hear you improved your situation! In the good old days they used to say "tune up on ku and your c-band will be fine!" Don't know if that's always true, with these news c/ku lnbfs since I have yet to take the plunge for one. Big dish was a learning event just like going to digital is.

 

[KE4EST]

In the good old days they used to say "tune up on ku and your c-band will be fine!" Don't know if that's always true, with these news c/ku lnbfs since I have yet to take the plunge for one. Big dish was a learning event just like going to digital is.

For the most part it is still true. If I do mine that way, and it is spot on except for 87W C. Now this is just me, 87 still needs a bump here and there to get what I want, may not be true for everybody.

 

[FaT Air]

My next challenge is to improve the Ku band reception (it is extreeeeemly sharp and touchy)

How true on a BUD. The beamwidth, on a BUD, on C band may be 1.5°. At Ku freqs it's probably only .4°, or less. The "tweaking" has to be made in even smaller increments. No problem with the "delay" as we knew you'd be busy. Glad to hear it's worked out.