Fine Tune 4DTV 920

[linuxman]

Ok, for those of you who have been following this thread, here is a technical question.

First the parameters. I measured this dish before I put it up, and here is what I found.

The diameter is 90-1/4" (229.2 cm) from the very top of the circle angle to the other side. This is only the area that can be seen by the feed-horn.

The depth is 14-3/4" (37.5 cm) using 2 strings from the same edge as above.

The factory specs on this dish from a sheet I got from a former dealer, are:

Focal length 33.75"
F/D ratio is .375

Using the figure above and the calculator from SatLex, I get these figures:

Focal length of 34.5" (87.55 cm)
F/D ratio of .38

Why is there a difference between the measured and calculated specs versus the factory specs?

Do they know something about this dish that I don't? Or did they just do a CYA maneuver?

I currently have the focal length set at about 33.5" which puts it at about 1/4" inside the mouth of the co-rotor, because I couldn't get the support arms to reach out further. I have the F/D ratio set at .38, and that is where I currently get the best signal.

Should I make some adapters for the support arms to move the scaler ring/co-rotor out to where the calculated distance should be?

If I bend the support arms where the slots are, I might be able to get to the 33.75" specified by the sheet, but never to the 34.5" calculated length without modification. I would rather make adjustable adapters than try bending arms.

The chances of getting all four to bend precisely at the same place and the feed-horn pointing precisely to the center of the dish is very slim.

Thanks for all your explanations and answers.

Fred

 

[gabshere]

could you use spacers/ bushings to gain the 3/4 inch and longer bolts

mine allowed to adjust the arms inward and out and i ( push in "closer" push out "further") gained a little bit (didn't know if thats standard) but heres where i have the problem and need at least a day and alot of pacients to adjust properly lol

 

[linuxman]

It's possible to put in longer bolts, or even all-threads and washers to extend out the arms.

The problem with that method is that all of that would have to be done on the dish side of the scalar ring, and might cause signal loss. It is also not easy to adjust for precise centering of the dish.

I have slid out the slots as far as they will go to get where I am.

I am thinking of perhaps an L shaped angle piece that bolts to the scalar ring on the cover side, and extends past the cover, then another L shaped angle piece with slots that bolts to the existing support arms, but when the two angles are bolted together, form an adjustable extension for the feed-horn to move it out further.

Just my first thought.

Fred

 

[linuxman]

I have 4 of these little pieces laying in my shop. I hardly ever throw anything away.

I could either use them as is, and run all threads from the support arms to these guys with nuts and adjust them out.

Or put them in the vise and make them L shaped and turn the long piece upright, and get 4 other pieces to fit to the scalar ring bolts and extend out past the cover to meet up with these guys and use wing nuts and bolts for a sliding adjustment.



It can be done pretty easily.

The question still remains, should I go with the factory specs, or the calculated one?

 

[voomvoom]

Hi Fred. Why don't you go ahead and try both? We all know you're going to anyway, in the long run. All that really remains, is when you tell us, which one worked!

Al

 

[linuxman]

Hi Fred. Why don't you go ahead and try both? We all know you're going to anyway, in the long run. All that really remains, is when you tell us, which one worked!

Al

How did you know I was going to do it?

You got me rolling on the floor laughing.

I quess you are right. I probably will try it. I used that calculator on the Birdview, and it was right on.

I probably won't be able to until Friday or so. Supposed to rain until then. I have to put in a little shop time to engineer the brackets.

I was just in hopes that some technical guru could give me a good reason why Perfect 10 decided to use the specs they used.

While I got you on the phone here Al, how do you set up a generic satellite in the 920, or can you point me to a link that tells me how?

Fred

 

[voomvoom]

It should program like any other sat, just go through the program set-up in the menu. You will probably need to find the sat though, the automatic won't work for a non-existant sat. Go to either AMC11 or G13 first, then Options, 6, 4, 4, then choose the generic you desire (make sure it has analog channels in it). Then bump the dish over, till you get a signal. You could hook your DVB up to the ku from the lnb and put it on the White Springs channel, so you'll know when you're on T7/IA7/G27. Good luck!

Al

 

[linuxman]

Cool!!!

Thanks Al!!!

Fred

 

[linuxman]

Just wanted to update.

Wednesday evening, I was programming away on the various satellites working my way East from T7 (IA13/H1), got over to the Anik birds, and is my normal routine, once I get the C-Band side, I move to the Ku side, and program in that sat at the same position. I had just gotten through doing the Ku on the farthest west Anik satellite, and suddenly I remembered reading something here about not doing something with the Anik birds. Quickly moved away from that position and saved 20 or 30 clicks away.

Hopped on the forum here, and did a search about Starchoice sats. Found the info, and looked at Diagnostic Screen G. Sure enough, the count was at 1920. I bet I wasn't on that bird for more than two minutes, but too late.

Went ahead and swung over to G1 and did the master reset.

Thursday morning had to go to a client. Called the former Perfect 10 dealer I know, and asked about the Focal length, and the calculated Focal length. He said he always set them at 34-1/4" which is probably fine for C-Band only. So when I got home yesterday, I tried that after the rain, and in between drizzles, cold wind etc. Made the signal worse for me.

I had stopped by Lowes on the way home, and bought some materials to make some brackets to extend my focal length to the calculated 34.5". So I spent the morning making brackets by hand. Took them up to the roof, and assembled them. I had forgotten that if you spread the support arms apart, it raises the feed-horn, so even with the brackets I had made upside down, the focal length was now at 37.5 inches.

I sat there thinking about how I could remedy the situation, and I took the piece that I had used in the picture the other day, and flattened it out, and made just a simple one piece extender for the support arms.

Put it together, and right now the focal length is at 34.5", but that comes right at the mouth opening. It needs to be inside about 1/4". So I will have to turn the bracket around, and fit it in the other way for it to adjust any further in.

The results for right now, no different than I had. I am hoping by hitting the sweet spot, I will see a change for the better.

I think the proof that the calculated focal length is the correct one, lies in the fact that I didn't lose any signal. If it was way off, the signal would have dropped like a rock.

I have to spend all day at a client tomorrow, so I won't be able to try anything else until maybe late tomorrow or Sunday afternoon.

I believe I will be able to get a little better signal when I am finished.

Fred

 

[linuxman]

Finally!!

I got the Focal length set properly at 34.5" like the calculator said it should be.

It increased the signal about 5 points across the board, so it was worth it.

I had to mount the support arms under the scaler rings to get it to that distance. Ended up not using any of my brackets that I so carefully hand made.

Tomorrow I will slave the Pansat to it and do the final fine tune of East/West, Elev/Dec. I am a little hampered by there not being much on the East side in the way of digital Ku signal and what there is, doesn't allow me enough time to run up and do any adjustment. I can't very easily do the adjusting on the West side because when the dish is pointed to a far sat on the West, it hangs out over about 20' of space.

If I don't get what I want after that, I have a couple of other LNBs to try on it. I didn't want to make any changes like that until after I had finished the actual tuning.

The moral to this story I think is, don't put up a 7.5' dish unless it is manufactured by a good reputable company that makes quality dishes, and has an almost perfect parabolic form. All the fine tuning you can do won't bring in what's not there.

You can't put in what God left out!!

Fred

 

[gabshere]

well i think the birdview spoiled ya , now your trying to get em all to read like that even if it doesn't put up the numbers its a good looking dish.

 

[voomvoom]

well i think the birdview spoiled ya , now your trying to get em all to read like that even if it doesn't put up the numbers its a good looking dish.

Hey Fred, I agree totally with gabshire. The 7 1/2'er isn't going to be in the same league, much less the same ball park. From what I've been reading, I think it's got better numbers than my 10' Unimesh. I'm sure it will be a fine dish, and you won't have to replace it with another Birdview. So, you can send the other Birdview(s) you have laying around, or soon to be laying around, in my direction. And, Thanks in Advance!

Al

 

[linuxman]

Hey George and Al!!

You are probably right.

The Birdview has spoiled me forever. What is sad, is that the old Winegard as unstable as it was in the wind, and as many hail dents and imperfections as it had, got better signal than this one. But you are right, it was a 10 foot dish, and this one is probably not in the same league as it either.

As far as the other Birdviews that I might have in the future. If I get the solid one, it is coming home here, with the intent of building another mount and putting it out on the middle of the roof by next fall, and doing away with the dish on the side except maybe for testing purposes.

Any other Birdviews after that, we can negotiate.

After the final tuning this afternoon, I can finally start putting up the Pinnacle for the family.

Thanks for the encouragement!

Fred

 

[linuxman]

I feel much better after putting slaving the Pansat to the 920 and checking sq strength on a few satellites. Made a couple of adjustments to line it up with the arc a little better.

With the Pansat, I get these SQ readings:

AMC6 (K6) 12052 V 90%
SBS6 (B6) ONN H 75% seemed a little down today.
G11 (GB) 12060 V 60 - 65% My TS satellite
G10 (X0) 11719 V 60%
G27 (IA7) White Springs 75% seemed a little down today too.

I also got the test card on AMC2 with the Pansat. Still can't get the test card on AMC2 with the 920.

Very low signal on AMC3. Only 15% on Montana PBS.

Didn't test the C-Band side with the Pansat. It seems to be doing ok.

If it cools down a little later, (85F now which translates into 95F on the roof) I might try a switch out with the Ku LNB and see if it helps the 920. I am currently using an Eagle Aspen .6 LNB that was new last August.

I have a Cal-Amp .6db LNB here with a higher gain on it that I got from George in a swap deal. It might work better with the 4DTV than what I am using.

I am glad I hooked up the Pansat, because I used it to set all the satellite positions on the East side of the arc, and to program in a couple of generics elsewhere.

I am finally nearing the end of this setup. Whew!!!

Fred

 

[gabshere]

the cal amp should do well even those generic white ones should do well )
did you receive the c band lnb yet

have fun and watch your step up there ....

 

[linuxman]

Hey George,

I thought I might do some switching out this evening between the Cal-amp, and the two white ones, and the new C-Band which got here today.

I'll probably put them on and run them for a day or two just to see how they are working.

Fred

 

[gabshere]

ok great..... i bet it will act like a new dish

those #'s listed above are the Eagle Aspen .6 KU LNB right

 

[linuxman]

That is correct.

I currently have an Eagle Aspen .6 and was using it and the Chaparral 20K C-Band on the old Winegard. Both worked great for DVB on the old dish.

I guess some LNBs work good if what they are being fed is good, and maybe not so good if they aren't.

Fred

 

[gabshere]

well i had that .6 & 17k corotor on and got 69% SQ on both c & ku with the new one i got 87% SQ so i thought that was a good improvement

 

[linuxman]

I hope you are right!!!

I would like to see that much improvement.

Fred