New KU hookup, questions

[trscott]

I just replaced my C-band feedhorn with a new Corotor II+, and Norsat LNBs for C/KU:

1) When I first hooked up the polarizer servo's wires, it started buzzing and wouldn't quit. I disconnected it and reconnected the old one and it didn't buzz, so was going to replace the new one with the old one, but when I unscrewed it, the buzzing stopped. I decided maybe it might settle down if I went in to the setup screens and tried to re-adjust it. That seemed to work. But I'm still not really sure what I did.
Question: Any idea what this was all about?

2) To my surprise, the standard Paraclipse feedhorn weather-shroud didn't quite fit the new feedhorn and LNBs and I had to cut a notch out of the bottom of it to clear the KU LNB. It was just about 1/2" too wide for the shroud. For now it is just cut out, but I will probably fabricate a fiberglass bulge addition to close it up once I get everything fully checked out. I did fully weatherproof all the connections with the parts you included and with some no-oxide sealer in the wire nuts for the servo.
Question: Is it possible to get one that might fit?

3) I don't have a lot of signal to spare on KU. I gather from what I have read that it is pretty demanding.
a) My DSR 922 says I have a signal of 100 and Quality=39 to 41 on TCM (X4-255), 100/49 on FMC (X4-251), and 100/51 on LMC (X4-253). Are those values reasonable? Or should I be able to do better?
b) Every time I switch to TCM (X4-255) it comes up with a lot of digital pixilated blocks and skipping audio. If I just key in the channel number several times, 255, 255, 255, etc., it will finally lock in. Other channels do not require this tweaking like TCM.
Question: Is this just characteristic of a marginal signal? It's not really an adjustment of the dish or skew, because I don't have to change them. It’s almost like the frequency detector has to get centered a couple times to finally lock in. The picture looks perfect once it locks in.

4) I figured I would look at what I could do to tune up the dish.
a) The feedhorn is not quite centered on the dish (12' dish though, so maybe it is a bit forgiving). The shepherds-hook style center post is in good shape, but the guy wires were quite loose. I figured that in 15 or 20 years of being battered by our high winds, they've stretched a bit. I took a whack at tightening them and re-centering the horn, but I was running out of daylight and one of the screw adjusters was too rusted to budge. I would guess the feedhorn is probably now within about 1.5" of the center of the dish (as measured from horn center to dish rim), but I should be able to get it better than that.
b) The dish frame looks like it is quite straight, with no noticeable .
c) The mesh is an expanded metal mesh with about 0.16" (~5/32") openings, I assume that mesh is fine enough for KU?
d) The F/D spec for the dish is .375, so I adjusted the feedhorn ring just shy of the .38 markings, and got it as perpendicular as I could.
e) The coax is quite old (maybe 15 years or so), but I trimmed it back and re-terminated the KU end. The inner dielectric looked quite clean, and the center conductor was un-tarnished, so I think it is probably okay, but I don't have any test gear capable of testing it at the operating frequency.
f) I haven't tried re-aligning the dish azimuth or elevation adjustments; I'm a bit reluctant to mess with them unless I have to. It has been fine with C-band, but I realize that the KU alignment might be enough more critical to require some tweaking.
Question: Anything else I should do? How critically should I adjust the feedhorn centering? And should I try to tweak the dish mount?

It is great getting these extra channels, but I want to do whatever I can to make the signal more robust.

Any other thoughts?

 

[TNGTony]

What Ku satellite are you aiming at to get TMC, FMC and LMC?

See ya
Tony

 

[drhydro]

Trscott,
Having your feedhorn centered is very critical, being off even a 1/2 " will affect signal quality. Remember the focal point is about the size of a golf ball, so get your feed horn as centered as you can. Being off an inch and a half will definately negatively affect your signal quality.

Tony,
Those channels are 4DTV (digicipher) on galaxy g4 (x4).

 

[trscott]

to TNGTony,

As I indicated above, I am tuning to satellite X4 (KU) to get FMC, LMC, and TCM on channels 251, 253, and 255 respectively.

 

[Shawn95GT]

My feed horn was off and getting it re-centered GREATLY improved my Ku signal.

I'm still not happy with my dish's Ku performance. Whenever I get my 8' dish up I'll be EXTRA diligent to get it dead on.

 

[trscott]

To measure and adjust feedhorn centering...

Okay, so I need to get this thing really dialed in (feedhorn centering). Seems to me that will require two things.

1) A better mechanism for adjusting the guy wires that center the shepherds-hook feedhorn mount. Right now these just pass through holes at the rim of the dish at about 10, 2, and 6 (clock face), and have screw clamps holding them. Pretty tough to do an accurate adjustment. You have to loosen them, pull the cable by hand, and then tighten it without letting it slip. I guess I could use a small vise grip to hold it temporarily while I tighten the clamp, but a vernier screw adjuster of some design would be much nicer. Maybe a pulley block and a turnbuckle anchored to the frame... Anything commercial out there that is recomended for this? I could make something on the lathe... (see crude sketch attached...)

2) A better method for measuring the distance from the horn to the dish rim. SUGGESTION for your consideration: It occurred to me that I could take an old feedhorn cap (or even the new one if I didn't already have an old one), drill a small hole right in the center of it, feed a piece of non-stretch fishing line , or kite string (spectra or the equivalent, which I already have) through the hole and knot it, and then use marks on the string to measure the point to the dish rim. I was using a tape measure, but its hard to get it dead straight, and to find the right place to measure to. The string would always be perfectly anchored right in the middle of the feedhorn throat, and can easily measure right to the face of the dish. What do you think?

 

[Shawn95GT]

They sell a tool that should be easy to fabricate. Basicly it's a laser pointer you put at the center of the dish and center the dot on the feedcorn cap.

I used a tape measure at four points around the dish to the scaler ring. It's easier on a little dish .

Shawn

 

[drhydro]

1)i like the idea of turnbuckles for adjusting your guy wires, should work awesome.

2) i think the string idea is a good one, you could also use a laser pointer if you can get it perfectly aligned on the feedhorn cap.

 

[trscott]

laser pointer issues

The challenge I see with the laser pointer alignment, is that it is only going to be as good as the perpendicularity of the laser beam relative to the dish center plate. A one degree error from perpencicular with the center of the dish would be more than one inch of lateral error at the feedhorn throat. I suspect that laser pointers don't have anything like that much precision in their laser diode mounting and aiming. Getting the perpendicularity of your measurement system correct is then probably no easier than centering the feedhorn, so you haven't really helped matters, just created a new problem to solve.

I suppose if you bought a commercial aiming device that was guaranteed to be calibrated for perpendicularity, but even then you are assuming the center plate is exactly perpendicular, and any small error in that center plate would have relatively little impact on total signal reception. I think measuring the distance to the circumference of the dish from the center of the feedhorn cap is the most meaningful and easiest measurement to do.

Another use of the string attached to the throat cap would be to secure the other end of the string to the center of the dish and use a carpenter's square to verify the perpendicularity of the feedhorn throat to the dish center-axis.

 

[WyrTwister]

Okay, so I need to get this thing really dialed in (feedhorn centering). Seems to me that will require two things.
1) A better mechanism for adjusting the guy wires that center the shepherds-hook feedhorn mount. Right now these just pass through holes at the rim of the dish at about 10, 2, and 6 (clock face), and have screw clamps holding them. Pretty tough to do an accurate adjustment. You have to loosen them, pull the cable by hand, and then tighten it without letting it slip. I guess I could use a small vise grip to hold it temporarily while I tighten the clamp, but a vernier screw adjuster of some design would be much nicer. Maybe a pulley block and a turnbuckle anchored to the frame... Anything commercial out there that is recomended for this? I could make something on the lathe... (see crude sketch attached...)



Use small turnbuckles on your guy wires .




2) A better method for measuring the distance from the horn to the dish rim. SUGGESTION for your consideration: It occurred to me that I could take an old feedhorn cap (or even the new one if I didn't already have an old one), drill a small hole right in the center of it, feed a piece of non-stretch fishing line , or kite string (spectra or the equivalent, which I already have) through the hole and knot it, and then use marks on the string to measure the point to the dish rim. I was using a tape measure, but its hard to get it dead straight, and to find the right place to measure to. The string would always be perfectly anchored right in the middle of the feedhorn throat, and can easily measure right to the face of the dish. What do you think?



If a yard or meter stick , use it . If not , naything from an old fishing pole to a piece of pipe . Put marks on it where the " rod " hits the rim of the dish ( where the guy wire is attached ) , touch the other end to the scalar ring , where the guy wire attaches .


Wyr

 

[trscott]

Guy wire pulleys & turnbuckles

I went ahead and built a pulley and turnbuckle adjuster for my sat dish and took some pictures. This is a 12' Paraclipse dish.

The first picture shows the rusted original guy wire clamp which was not conducive to precise adjustments.

The next three show the mounting of a ball bearing pulley, and turnbuckle to make adjusting the feedhorn guy wires much easier. I only had to drill one new hole in the frame for each of four guy wires. The turnbuckle mounted on longer frame bolt to give it some clearance from the frame.

 

[gizzer777]

Looks like you did a great job! The manufacturers should have thought of that!
jeff

 

[WyrTwister]

Looks like you did a great job! The manufacturers should have thought of that!
jeff

You forget , the factory method was cheaper . :-(

Wyr

 

[dfergie]

nice