Offset v prime focus chat

FRINGE

FRINGE

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Adeje in Tenerife
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laminas 2.7 offset
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Tenerife
I have an offset dish. My friend (2 doors down the road) has a 3m petal prime focus dish. In general, my reception appears to be better than theirs at times but that proves nothing (about the dish) because we have different LNB's, different receivers, different cable lengths and probably different cable quality. Don't think its possible to provide a meaningful definitive accurate technical assessment of the two dish types in use. The research I did before my installation (after my friends prime focus) suggested that an offset dish design was more efficient but I guess that does not necessarily mean it is 'better' (or worse) when compared to a comparable sized prime focus. What I do know is that my dish is a more solid design/structure and is less susceptible to wind (misalignment) than my friends flimsier setup and for me, in a fringe reception area, that's a bonus.
 
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Ok I am sorry to bring an old thread up :D, but reading through this I am still unsure what's better than what ? anyone have a change of opinion with more experience in and around satellite dishes ?.
 
RimaNTSS

RimaNTSS

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I do not think much is changed in 4 years. PFA and offset both have pluses and minuses. Which is better..... depends on criteria you apply to compare them.
 
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I do not think much is changed in 4 years. PFA and offset both have pluses and minuses. Which is better..... depends on criteria you apply to compare them.
Well to me there is only one way to compare dishes Rimants and that's on performance, from my reading on a clear day a size for size comparison and good quality dishes a prime focus will perform better than a O/S dish ?, surely they must be an advantage at the ends of the arc with a prime focus ?
 
RimaNTSS

RimaNTSS

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Some SAT-related hardware.
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Firstly, we do not compare performance of the dishes but SAT-systems (dish, LNB, connectors, cables, and receiver). If we can use same receiver (finder to measure signal level) and more or less same cables and connectors, than we left with different LNBs (one for PFA and another one for offset) and different dishes. As it mentioned earlier in the thread, shadow effect on PFA has very little influence on final performance of sat-system. But then we also challenged by frustration of received signals and it happens not only during long period of time but also happens within seconds. My personal feeling is that performance of sat-systems with same size PFA and O/S dishes, with proper LNBs will perform same. If there is going to be difference in performance than amateurs like me (and maybe some others here) will not be able to notice.
 
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Silly question Rimants ? would a PF dish need less height to clear an obstacle than a OS dish? or are they both the same please ?.
 
Captain Jack

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Only if it's higher up. The satellite is still beaming from exactly the same spot, so the same obstruction restrictions would apply.
 
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Only if it's higher up. The satellite is still beaming from exactly the same spot, so the same obstruction restrictions would apply.
Thanks Alex I know its beaming form the same place, its just looking at them after looking at OS dishes, thought it was a silly Q but had to ask :)
 
Captain Jack

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Well... actually... a PF dish mounted on the same pole/mount would have the bottom of the dish higher up than an offset, so that would technically be higher as a whole. But we are talking inches here.
 
RimaNTSS

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Silly question is only that which was never asked. ;) If you look from the very bottom of the dish towards satellite and there are no obstacles than reception should be OK. And this applies to both PFA and O/S
 
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Silly question is only that which was never asked. ;) If you look from the very bottom of the dish towards satellite and there are no obstacles than reception should be OK. And this applies to both PFA and O/S
Thanks Rimants, they will be no obstructions for me it just made me wonder that's all,

Another question, Two identical OS antennas both pointing at 70.5E ones fixed the other is on a polar mount, would the fixed dish receive more signal than the one on a polar mount ?.
 
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Two identical OS antennas both pointing at 70.5E ones fixed the other is on a polar mount, would the fixed dish receive more signal than the one on a polar mount ?.
Definitely, if polar-mounted antenna system is properly tuned to the Clarke belt than it will perform exactly same as fixed antenna system but on each of the satellites.
 
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Definitely, if polar-mounted antenna system is properly tuned to the Clarke belt than it will perform exactly same as fixed antenna system but on each of the satellites.
Thanks again, i was led to believe that the one on the polar mount would loose signal to the one aiming the full face at the sat that's another myth then.
 
RimaNTSS

RimaNTSS

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I would even say more: polar-mounted Offset antenna system will perform exactly the same as Az/El offset antenna system, but only on central satellites. On satellites which are more East or more West, offset antenna system will outperform Az/El antenna system. In case of PFA, results will be exactly the same.
 
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I would even say more: polar-mounted Offset antenna system will perform exactly the same as Az/El offset antenna system, but only on central satellites. On satellites which are more East or more West, offset antenna system will outperform Az/El antenna system. In case of PFA, results will be exactly the same.
:confusedMake your mind up Rimants :D, i wasn't talking central i was talking one slewed to 70.5 on a pm and a fixed pointing at 70.5, and obviously both tuned.
 
RimaNTSS

RimaNTSS

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Central I meant Due-South. If your Due-South satellite is 0,8*W than, for your location for 70,58E , performance of PM system (if properly tuned) will be better than OS system.
 
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Sorry Rimants i am still none the wiser. lets start again.

Another question, Two identical OS antennas both pointing at 70.5E ones fixed the other is on a polar mount, would the fixed dish receive more signal than the one on a polar mount ?.
Ok my due satellite is 0,8W and both dishes are pointing at 70.5, option 1 PM will be better ? option 2 fixed dish will be better? option 3 both the same ?.
 
RimaNTSS

RimaNTSS

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Option #1 will be better.
 
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So an offset dish performs better slewed over to 70.5e than the same fixed dish pointing at the same satellite :confused i will work that one out tomorrow:), thanks for you time Rimants :)
 
J

joddle

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2x Pace 2600 C1 (in a box just in case) , 3 x Humax HD Foxstat (2 of which in store as spares) . 3x Manhatten Plaza - Pasat 2.4 PF dish mounted on flat roof with Invacom C120 quad LNB .
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Massanassa, Valencia, Spain
I often wondered about the differences between PF and offset - to me the offset seems if could induce more phase shift problems as it means that although a circle is presented to the signal, the differences in the distance the signal travels from the reflective surface of the dish to the LNB must be very much greater from the top of the dish that at the bottom and that difference is more than would be experienced in a PF dish of the same nominal size. I suppose what I am querying is would that small difference actually be relevant when it comes to signal quality being seen at the LNB?
 
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