Conical Scalar position on C Band LNB for CM180

dishdx

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Hello!
1) What should be right position of conical scalar on Titanium C2W PLL LNB? I placed it on maximum of signal aprox. on number "42". I saw how measure F/D ratio for prime focus, but for my Offset Channel Master 180 i don´t know:-( Can you help me please?

2) And second question. I tested the position of C band LNB in LNB holder, and best results are when LNB is quite more back than Ku... (nearer to the top of LNB arm) But attached picture says that position is more to front (nearer to dish)... ?

3)
Why is skew not significant on C band like on Ku? Im on Thaicom 78.5 and the skew should be 36%... but i have 0% with best results...

Thank you!
 

Channel Hopper

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You will not have a direct calculation of ratio on an offset dish, but as an approximation, the measured or calculated focal point of any dish should be inside the C band feed by approximately 1.5 cm

Thaicom is linear polarity so there will be a skew offset that improves the signal. Have you left the dielectric plate inside ?
 

dishdx

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Yes, on Thaicom i use it without plate (fo R/L sats i use DocOfSat, Pride design - very good!). But no skew effect on linear:-o ....or very very marginal... will check again later today.
How do you mean it with 1.5 cm? This dimension on picture should be 1,5?
 

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John

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Yes, on Thaicom i use it without plate (fo R/L sats i use DocOfSat, Pride design - very good!). But no skew effect on linear:-o ....or very very marginal... will check again later today.
How do you mean it with 1.5 cm? This dimension on picture should be 1,5?


Channel Hopper's reference to 1.5cm is relating to the point where the signal is focused at within the front of the feed (behind the blue cap) . When i had my 1.8 CM dish in use i tuned the focal point first without the scalar for maximum 'signal strength'. Then i fitted the scalar ring and manually adjusted for best 'Quality' or S/N readings. I found from experience that using a conical scalar on the 1.8 CM was a bit 'wooley'.. ie: hard to find the exact position for best performance. Totally different on my 2.2 Prime focus where i can adjust the flat scalar to + /- 1mm to show definite differences in S/N.
 

dishdx

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Thank you John. Im not sure if i will have signal without ring:-) I will try to do it on some strong sat. It´s good idea. I have prime focus scalar too,i will try to put on the lnb if there will be some difference:-)
 

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Thank you John. Im not sure if i will have signal without ring:-) I will try to do it on some strong sat. It´s good idea. I have prime focus scalar too,i will try to put on the lnb if there will be some difference:-)



Using the flat scalar on a CM offset will be worse as it's a different concept. You can try though just to satisfy your curiousity
 

dishdx

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Friends, no SKEW efect on C band on my CM180 with Titanimum C2WPLL. I dont understand... on my QTH should be skew more then 30°best... but signal is best on 0.... i remember that on other satellites near horizont was it the same... On Ku it is very significant on C band not... strange world:-))
 

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It is significant on C-band, take some images of the feed throat, just in case there is something others can pinpoint.
 

dishdx

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ok, i will make next days photo!
 

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something others can pinpoint.
for example - depolarization plate for circularly-polarized signals, than skew of the LNB does not matter. Just a guess.
 

dishdx

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Sure, but the plate is not inserted:-) will make photo and video
 
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