You need to make sure the Dish is "square" (for a lack of a better term) to the Tube first.
Usually there is a bolt that goes through the Tube, so the clamp can't slip.
not on this one. A pair of U-bolts hold the dish (FS 120cm) to the HH120 tube.
When I originally installed the 90cm on that hh120, I used a weld line, mold mark, or whatever it is on the HH120 tube that was right along the 0 marking on the tube as a South centerline and put my 90cm FS bracket on the tube, lining up that centerline of the hh120 with something that looked to be centerline on the 90cm bracket.
Today, I did my East position - I had to push up on the dish from behind to get better signal. West was the same way the day before. Printing out the alignment troubleshooting page from the hh120 manual on this site, it told me I had to adjust the elevation of the HH120 motor (not of the dish) so I changed it from my correct latitude to the next latitude marking and tightened it down. I went back to 0 position, redid the elevation with my jig, took off the jig and E and W are still off (push up on the back of the dish to get better signal on both ends). I am beginning to wonder how accurate the elevation setup markings on the HH120 motor are and I guess I'll play with it degree by degree until I find where the arc is tracking right.
I also did the push/pull test with my dish at 0 postion and I"m trying to figure out something. I can push up on the dish from behind and get better signal than I did when my jig was on the dish and used the jig to maximize signal level. I am wondering that means the weight of the invacom qph-031 is slightly deforming my dish and when I do my dish push test, I'm relieving some of the weight of the invacom from the dish, bring the dish into better alignment and resulting in better signal. I may have to do my dish aiming with a light LNBF and then put the invacom back on it when I'm done getting the dish properly aligned. Yes, I'll probably lose signal with the invacom on it, but I should have a little bit more signal to begin with, I'd think, making that slight loss of signal while using the invacom not as significant.