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Thread: What are these scalar rings telling me?

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    Default What are these scalar rings telling me?

    A while back I acquired a 1.5m solid dish from a demolished classroom at a local school.

    [IMG][/IMG]

    The focal length measures out at around 600mm, yielding a F/D of around 0.4

    The dish came complete with a Universal LNB dangling from the end of the coax (for how long, nobody knows) and without a cap on the feedhorn, so there were a few tenants in there.

    Needless to say, it appears to be lifeless.

    I bought a Satking 10700 Prime Focus LNB to try out on the dish....the product description for this LNB states:

    "Satking Prime Focus 10700 LNB to suit old style Big 1m Solid dish OR 1.2m Andrews Dish. "

    In purchasing it I figured that, based on the above, there was a chance it might not like the 1.5m dish.

    Here is the old LNB that came with the dish (on the left) compared to the new Satking LNB (on the right).

    [IMG][/IMG]

    Quite a bit of difference in the Scalar rings.

    Any thoughts on how the new LNB might perform on the 1.5m dish?

    Is the difference in scalar rings likely to affect performance?



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    Scalar rings reject signals from outside the dish surface and focus so they are matched to the dish, particularly commercial dishes.

    Scalar rings also concentrate the weaker desired signal from the edges of the dish back into the centre, once again, matching dish parameters.

    The size and spacing of the rings also relates to wavelength.

    In your case, the best thing to do is try it.

    BTW, nice job on restoring the dish... looks good.

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    All good, MTV.

    Fired it up last night and couldn't find a damn thing.

    Back at it this morning - still no response on the meter looking for IS19 Ku transponders previously stored from my existing 90cm offset.

    In desperation, positioned the dish where I reckoned it should be, using (for the first time) the spectrum analyser in the meter found something that looked like a satellite, and did a blind scan.

    Sure enough, it was IS19...problem had been that TPs previously scanned in from the offset LNB were 12286, 12526, and 12726.

    But the prime focus LNB scanned them in as 12289, 12529, and 12729.

    I had been looking for the freqs stored in the meter from the offset, and the meter wasn't buying what was coming out of the Prime Focus.

    Cost me a couple of hours, but something learned.

    Comparative meter measurements at the LNBs:

    90cm Offset: SS - 84dBuV

    1.5m PF: SS - 98dBuV

    Meter measurement downstream of the multiswitch:

    Offset SS/SQ: 93/72

    PF SS/SQ: 93/86

    So, looks like things are working OK.

    Only loose end is bloody hard to tune out phantom vertical echoes of the horizontal TPs.
    Difference between "there" and "not there" is a very small tweak of the skew.

    Current setup on home-brew tripod is a bit wonky - once set up on a solid mast just might be able to squeeze a bit more out of it.

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    Good you got it working.

    The Freq difference would be due to the deferring LO between the two LNB's 10600 and 10700

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    In your receiver (signal meter?) setup do you have the option to change the LO frequency?

    For instance here in the US there are two sats parked almost on top of each other Echo14 at 119.0w and Anik F3 at 118.8!

    To see both you need a SINGLE universal LNB with the LO set at 10750 instead of the normal 11250! The receivers LO range adjust varies well below and above those two freqs and and is user definable! The Echosat is normally 11250 on it's own but the piggyback sat is at 10750. In antenna setup though, the LO freq is set at 10750 for both.

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    Quote Originally Posted by mtv View Post
    Good you got it working.

    The Freq difference would be due to the deferring LO between the two LNB's 10600 and 10700
    Sorry if this is silly on my part, but the frequencies are differing by about 3 MHz each time, wouldn't different LNBs with those LOs simply change it by 100 MHz each time, so that the frequency still ends on a 6 or a 9 for both LNBs?
    Last edited by irritant; 01-03-16 at 06:42 AM.

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    Quote Originally Posted by mtv View Post
    Good you got it working.

    The Freq difference would be due to the deferring LO between the two LNB's 10600 and 10700
    Both the existing offset LNB and the new Prime Focus LNB are 10700 LNBs.

    So I just assumed that what had been scanned into the meter previously with the Offset LNB would be OK for scanning with the Prime Focus....in theory it should have been.

    But it appears that the LO in the Prime Focus LNB may not be exactly 10700 and produces an IF that is 3 Mhz different to that produced by the Offset LNB.

    As a matter of interest, the specs for the Satking Prime Focus LNB state an initial LO accuracy of +- 1Mhz, and a temperature drift of +- 3Mhz.

    The offset LNB (Strong L802) I'm using has a LO stability figure of +_ 3 Mhz, but produces a TP frequency that is spot-on.

    Further investigation revealed that the Sat Meter was happy to receive both 12726 and 12729 (DVB-S) as the same signal.

    But it would not accept the 3Mhz difference in the case of 12286 and 12526.....presumably because both those transponders are DVB-S2, and tuning accordingly more critical.

    It was those two transponders that I was looking for....and not seeing.

    So, if I look for 12286 with the 12289 setting in the meter, nothing is seen....and vice-versa. Same with 12526/12529.

    I guess the lesson here is, when looking for a satellite cold-turkey use a DVB-S transponder (if one is available) for the initial search, and then go from there.

    Lesson learned

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    Quote Originally Posted by Thala Dan View Post
    Both the existing offset LNB and the new Prime Focus LNB are 10700 LNBs.
    Sorry for the confusion. I misread the universal you mentioned as being a 10600 LO

    The 'universal' LNB you mentioned was the dead one.

    The difference as you've discovered is still a shift in the LO.

    Tolerances.... a good thing to remember.

    Not a bad idea of initial alignment on a DVB-S transponder, if available.

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