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WISCOM

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Posts: 66
Reply with quote  #1 
I found after alot of tinkering with my 1.2m channel master dish.That the F/P is not where the bracket I started with the 1.0 Ku LNB that came with the dish on SES3 NBC as a test point.
NBC East sig 70 q 40% at best.A new LNBF(tested two)mounted on the bracket was about the same.
Moving the LNBF to the dish side of the bracket(used a 1 inch long pvc pipe glued to the back of the LNBF.I saw a gain of 12db on HDSDR .
NBC East sig 82 q 70%
This also brought in NC1-8 no chop or loss,NBC Mux 1-4 by 8%
Did not re-tweek the dish.
This might help some that are up north and have a hard time with SES 3
IMG_2386c.jpg 


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1.2m offset Ku .7 Ku LNB,1.2m L-band RHCP,90CM Ku.
12 el UHF cross yagi RHCP Meridian sat.
PR_Weast

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Reply with quote  #2 
What is your local area?
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Openbox S9,IPM HDconvert V5,10' BSC621-U & 241, 24"  135,133,131,127,125,123,121,118.8,
116.8,114.9,113,111,105,103,101,99,
97,95,93,91,89,87,83,81,78,72,70,65,
61,58,55,53,50,47,45,43,40.
39"2100 HH ku Univ.127.0 to 12.5W
sharpie

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Reply with quote  #3 
How far is your lnbf from the center of dish now?

Just checked mine and it is 36 inches
WISCOM

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Reply with quote  #4 
The West side of Green Bay,WI
From the center of the 4 bolts to the dish side of the LNBF 32 inchs,The mount is 36 inchs.

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1.2m offset Ku .7 Ku LNB,1.2m L-band RHCP,90CM Ku.
12 el UHF cross yagi RHCP Meridian sat.
WISCOM

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Posts: 66
Reply with quote  #5 
The specs I found online say
FL 720mm
Ku gain 43.32db
C band 32.78db 103w data lnbf at new fp.jpg 


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1.2m offset Ku .7 Ku LNB,1.2m L-band RHCP,90CM Ku.
12 el UHF cross yagi RHCP Meridian sat.
wejones

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Reply with quote  #6 
First, the focal distance isn't measured to the center of an offset dish.  The center of the paraboloid is usually just a bit off the bottom edge of the dish.
  I don't have the dish you have, but this sounds strange that the focal point would be off this far. If the focal position is that far off, it sounds like either you have the wrong LNBF arms or the dish was designed for a different style of LNBF.  If it that far off, it isn't easy to locate the focal point by using signal strength, since there is a tendency of maximizing a side lobe instead of the main lobe (ie when the focal distance is way off you might only have a donut shaped lobe, and you won't be aimed at the satellite, and if you maximize that, you'll be way off.
  I think that this might be a good time to try the mirror technique for locating the focal point.  Ie glue several small thin mirrors at various points, then manually aim the dish at the sun while holding a piece of paper or cardboard back near the lnbf bracket. It takes a bit of manipulation with both the aim and movement of the  piece of paper, but you eventually find a point where the reflections from the mirrors coalesce into a single spot.  When I did it, I glued the cardboard onto a piece of wood that fit into the lnbf holder and could be adjusted in/out. Then aimed the dish at the sun and raised and lowered the elevation of the dish while watching the spots dance around on the cardboard.  I would then repeat the experiment with the target wood/cardboard moved in/out at different positions until I located the focal point.  Sounds hard, but it really didn't take too long. 
   In your case, if you think you have found the focal point, you can just stick a piece of paper on the existing lnbf face and try it, to see how close you are. 
   BTW, I'm curious re what SDR you're using?


WISCOM

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Posts: 66
Reply with quote  #7 
The dish arms are for a long neck feed horn,my guess mid 90s ex sat to pager.It was free and I used it for L band Inmarsat untill now.The freed point is where the original f/p is.
SDR is a flightaware pro 2ppm.also a blue r820t2.as you know there max is only 2.4Mhzs wide.

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1.2m offset Ku .7 Ku LNB,1.2m L-band RHCP,90CM Ku.
12 el UHF cross yagi RHCP Meridian sat.
RimaNTSS

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Posts: 339
Reply with quote  #8 
@WISCOM Could you show pictures of your dish front and back? And also, if possible, picture of the stamp on the back of the mirror.
However, I think it is same dish as I have. Here is collage picture I made look at digits in yellow, those are for Channel Master 1.2m.
WISCOM

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Reply with quote  #9 
IMG_2384c.jpg 

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1.2m offset Ku .7 Ku LNB,1.2m L-band RHCP,90CM Ku.
12 el UHF cross yagi RHCP Meridian sat.
WISCOM

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Reply with quote  #10 
IMG_2375c.jpg 
this was befor the lnbf was moved


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1.2m offset Ku .7 Ku LNB,1.2m L-band RHCP,90CM Ku.
12 el UHF cross yagi RHCP Meridian sat.
WISCOM

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Reply with quote  #11 
IMG_2390c.jpg this is what was on the dish when we removed it from a tower

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1.2m offset Ku .7 Ku LNB,1.2m L-band RHCP,90CM Ku.
12 el UHF cross yagi RHCP Meridian sat.
RimaNTSS

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Posts: 339
Reply with quote  #12 
Yes, it is same dish. Use yellow digits from my collage to check whether  LNB is properly installed. I would advice (may I?) to make new holder like on my collage and you will get perfect SAT-system. Channel Master antennas are one of the best ones IMHO. Even they are old, but during the time lapse they do not change their shapes. Sometimes they need to get some wash though. If I was offered old Channel Master and any other nowadays new antenna, I would certainly choose Channel M.
And I am missing picture taken from the back of your dish to see the strength ribs.
wejones

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Reply with quote  #13 
Quote:
Originally Posted by WISCOM
The dish arms are for a long neck feed horn,my guess mid 90s ex sat to pager.It was free and I used it for L band Inmarsat untill now.The freed point is where the original f/p is.
SDR is a flightaware pro 2ppm.also a blue r820t2.as you know there max is only 2.4Mhzs wide.


Oh, OK re long neck feed. 
Re the SDR, OK, the image was a bit blurry, and I didn't read the freq axis, and thought that was a full band scan showing broad video signals on the trace. I should have known better.  [smile]    I have one of the cheap 2 MHz SDRs, and was looking for a reasonably priced replacement that could cover at least a single transponder, and was hoping you had found one.  The only ones I've seen are very expensive once they get up above a 20 MHz span. 
   I didn't know that there were so many narrow signals on SES-3. 


RimaNTSS

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Reply with quote  #14 
Quote:
Originally Posted by wejones
The center of the paraboloid is usually just a bit off the bottom edge of the dish.
Usually it is like that, but in case of Channel Master dishes (all sizes), the center of paraboloid is in the same spot as bottom point of the working area (point B on my collaged picture).
Also it is important to point LNB not to the very center of the dish but little bit lower (point G on the collage).
WISCOM

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Reply with quote  #15 
Quote:
Originally Posted by RimaNTSS
Yes, it is same dish. Use yellow digits from my collage to check whether  LNB is properly installed. I would advice (may I?) to make new holder like on my collage and you will get perfect SAT-system. Channel Master antennas are one of the best ones IMHO. Even they are old, but during the time lapse they do not change their shapes. Sometimes they need to get some wash though. If I was offered old Channel Master and any other nowadays new antenna, I would certainly choose Channel M.
And I am missing picture taken from the back of your dish to see the strength ribs.

Yes either a mod-ed mount on new arms,shorter once I find the sweet spot

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1.2m offset Ku .7 Ku LNB,1.2m L-band RHCP,90CM Ku.
12 el UHF cross yagi RHCP Meridian sat.
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