corotor & f/D calcs

[dunnsept]

OK, so my original corotor broke, ordered a new one, and it showed up last night. I put my LNBs on it, got it setup, and figured that now was a good time to re-check the f/D setting.
somebody please verify my calcs:
so, 108" dish, that's 17" deep should give an f of 42.8
so my f/D is .39
I think my buttonhook might be off or sagging because I get the best signal at 36 on the feedhorn.
anyway, so I put the new corotor II + on and get... nothing.
I think my LNB is dead, so I put on an old one and now I'm getting V but no H. so I don't think my feed is clocked properly, I was doing this around 9:15 and it was gettin kinda hard to see. (yes, the servo was moving)
anyway, anybody have any recommendations for a C-band LNB?
I was using was an Eagle Aspen SLT+ and I was quite happy with the results on that one. I think what's on there now is actually a Norsat, but it's original to the dish which puts it at about 25 years old.
Used to get Q of 99 and ebno of 11 on W5 with the SLT+, now I'm getting Q of 70 and ebno 6.8 with everything set as it was, just the older LNB

 

[Lak7]

What was the Old Feed f/d set to?

 

[dunnsept]

36.
When I put the new one in, I calc'd the f/D and set it at 40. Got absolutely nothing. backed it off to 36. got.. nothing.
put the old LNB on it and reset to 40.. got an EBNO of like 1. backed off to 36 and got ebno of 7 .. all of this was on W5 because I can use a short ladder to get to feedhorn and I know in the past I had a strong signal there

 

[1captain]

you're F/D should be set an never change it for that dish, if it calls for .39 set at it an leave it. if you need to move F/L in, the move the button hook in or out for best signal, but the F/D will remain the same for that dish.

 

[dunnsept]

OK, I can try that, but how on earth do you move the buttonhook in and out from the face of the dish? I never realized that it was really adjustable.
gonna measure the distance from front of feedhorn to dish face tonight if it quits raining.

but, other part of the post: anybody have any recommendations for a c-band LNB?

 

[sergei]

That could be a problem for you because it just depends on the type of dish you have, some are fixed and some can be moved. Both my Raydx dishes can be moved but the Winegard and Zenith dishes were both fixed in place. So you need to measure the dish and go from there.

So what type dish do you have?

 

[dunnsept]

that's a good question. I do not know what brand it is.. no labels or markings of any kind on it. 9' mesh with a buttonhook lnb arm. that's about all I can say about it.

 

[Cham]

Norsat is a good LNB, have had good luck so far.
A PLL might be a good option when getting into S2-8psk... Mine is 0.5MHz stability but I havn't tried it with an HD receiver yet. Soon I hope!
-C.

 

[pendragon]

It isn't terribly surprising that setting a lower f/D could lead to a better signal. After all most feeds are designed to taper off well before the edges of the dish. By using a lower f/D setting, you'll be using more of your dish. That's more gain and a tighter beamwidth. The danger of going too far is you'll start to raise your noise floor. I've been meaning to write a thread about f/D denial, because if you're careful, setting the 'wrong' f/D on your feed can provide very nice improvements. Some other time.

Getting the focal length set correctly should be your highest priority. With a corotor the focal point will normally be a bit inside of the feedhorn. Setting the f/D isn't quite as critical, but it's usually easier to make the adjustment before mounting the feedhorn as you probably won't need to change it.

I doubt that a PLL LNB will lead to a noticeable difference. A regular LNB with a decent frequency stability should be good enough. Looking at the specs, the equivalent noise temperature is a rough guide, but I expect some LNB manufacturers are not entirely honest about this spec. If the phase noise specs are given and are low, that is probably more likely to help on high rate, high FEC, 8PSK,... I'm using Norsat 8115s and those are very good performers for their price point. Something a little less would work well, too.

 

[dunnsept]

well, thanks for all the input. I went back last night and reset the feedhorn to 39. no signal at all. just in case, I rotated it through about 80 degrees. no signal at all.
pushed it in to 36, put it back to about an 11 o'clock position, voy oh lay! signal.
tweaked it a bit and all's fairly good again. My Q/ebno is nowhere near as high as it used to be with the other LNB, but is fairly good.
anyway, I then got out the tape measure and followed the directions in the corotor installation to measure focal distance. instructions say to measure from face of dish to 1/4" inside the throat of the feedhorn, with the scalar at 36, it puts the point 1/4" inside the throat to the focal distance of the dish.. at least mighty close to it. so, I guess something's just not right with the buttonhook on my dish.

I plan on doing some more testing/tweaking this weekend, make sure the feed is centered etc.
but I think I'll still pickup a new LNB to see what sort of difference it makes.

and yes, I do use this dish along with a pansat 2500 for DVB and a TT3600 for DVB-S2. I haven't tested it out yet but will this weekend. I was never able to lock RTN with it, but had a good pic on other S2 signals

 

[cruzin]

well, thanks for all the input. I went back last night and reset the feedhorn to 39. no signal at all. just in case, I rotated it through about 80 degrees. no signal at all.
pushed it in to 36, put it back to about an 11 o'clock position, voy oh lay! signal.
tweaked it a bit and all's fairly good again. My Q/ebno is nowhere near as high as it used to be with the other LNB, but is fairly good.
anyway, I then got out the tape measure and followed the directions in the corotor installation to measure focal distance. instructions say to measure from face of dish to 1/4" inside the throat of the feedhorn, with the scalar at 36, it puts the point 1/4" inside the throat to the focal distance of the dish.. at least mighty close to it. so, I guess something's just not right with the buttonhook on my dish.

I plan on doing some more testing/tweaking this weekend, make sure the feed is centered etc.
but I think I'll still pickup a new LNB to see what sort of difference it makes.

and yes, I do use this dish along with a pansat 2500 for DVB and a TT3600 for DVB-S2. I haven't tested it out yet but will this weekend. I was never able to lock RTN with it, but had a good pic on other S2 signals

Hope you get it all working, I have a question. as I am not familiar with the type of lnb you are using but was interested that you were trying to get RTN. is it the RTN that is on the sat at 83* amc9? I am setting up a c band and have bolted a ku lnb on the side of the scalar and plan on trying to get some ku sats when I get it moving properly as I am having trouble with the mover and or the new gbox. I must be fairly close to you as I am about 35 miles west of mt pleasant.