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DIRECTV Satellite Discussion D-14 @99W

Discussion in 'DIRECTV General Discussion' started by Sixto, Jun 17, 2010.

  1. Jun 27, 2013 #741 of 3078
    HoTat2

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    Huh? :confused:

    Your claim back in post #732 was that multi-frequency dish antenna designs depend on the band wavelengths being sufficiently diverse.

    Well not so, as in addition to the example I posted there's even a better case here of the dish 500/1000+ with two bands right beside and thus very close to one another, yet the LNB can still sufficiently separate them. The 12.2-12.7 GHz Ku BSS band is then directed to a receive circuit with a 11.250 GHz L.O. (14.350 GHz L.O. for the DPP upper block). And the 11.7-12.2 GHz Ku FSS band to a receive circuit with a 10.750 GHz L.O. (13.850 GHz L.O. for the DPP upper block).

    So what's your point now?
     
  2. Jun 27, 2013 #742 of 3078
    HoTat2

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    The point is since RB-1 and RB-2 are to be co-located with 99 and 103, the RDBS alignment can't be anymore different or sensitive than the Ka band, and is likely somewhat less due to its lower frequency.

    So if the Ka alignment is peaked correctly the RDBS must follow and be peaked as well.
     
  3. Jun 27, 2013 #743 of 3078
    cypherx

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    How do you think RDBS will handle rain fade? Similar, better or worse than Ka band?
     
  4. Jun 27, 2013 #744 of 3078
    bobnielsen

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    It should be similar to Ka, possibly slightly better.
     
  5. Jun 27, 2013 #745 of 3078
    James Long

    James Long Ready for Uplink! Staff Member Super Moderator DBSTalk Club

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    So a few days ago there needed to be a "decisive difference" and now the bands are "close enough"? :eek2:

    BTW: Thanks for accepting that the frequencies "probably" could be picked up on the same antenna. I happen to own that antenna. DISH has been selling them for years. There is absolutely no "probably" about it. :)
     
  6. Jun 27, 2013 #746 of 3078
    HoTat2

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    Though I think technically speaking, the two bands really wouldn't be picked up by the same "antenna." Since the dish is not actually an antenna, but an RF reflector. The "antennas" (note, plural in this case) are really a small pickup probes protruding into the rear portion of a short section of waveguide which serves as the feedhorn mouth on front end. One antenna pick up probe is needed for each band.
     
  7. Jun 27, 2013 #747 of 3078
    bobnielsen

    bobnielsen Éminence grise

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    I doubt it. Such a probe is typically located a quarter-wavelength from a shorted end of the waveguide and it would be difficult to locate two of them very close to each other without each interfering with the other.
     
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  8. Jun 27, 2013 #748 of 3078
    P Smith

    P Smith Mr. FixAnything

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    last models of LNBF using probes etched on PCB ... not sure how that 118.75W/110W combo made, perhaps I would dismantle one. Is someone has it broken ? :)
     
  9. Jun 27, 2013 #749 of 3078
    James Long

    James Long Ready for Uplink! Staff Member Super Moderator DBSTalk Club

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    Since his statement of FUD was that a dish receiving RDBS would not be protected under OTARD I'll stick with the FCC definition of antenna: "... video antennas including direct-to-home satellite dishes that are less than one meter (39.37") in diameter ..."

    I have seen nothing that proves that a RDBS receive apparatus (avoiding the "a" word) cannot be constructed within the bounds of OTARD protection.

    There is still no proof that an RDBS antenna will not be "OTARD compliant".
     
  10. Jun 27, 2013 #750 of 3078
    Diana C

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    Seems to me that a little outside the box thinking leads to a number of ways to skin the "two bands at one feedhorn" cat. For example, the Ku antenna ("antenna" being used in the strictest sense - the device that converts a microwave radio signal into an electrical signal) could use a metamaterial design that acts as an antenna to Ku frequencies, but is transparent to RDBS frequencies (and so the RDBS antenna could be behind the Ku). Or a similar metamaterial approach could be used to reflect or deflect one frequency band to a different focal point than the other. Metamaterials are used today in the "Flat Dish" designs.

    Of course, the simplest macro level design approach would be interleave the two antennas (although that calls for a more complicated circuit design). That way, they could both sit at the same spot in the feedhorn. (see next post)

    I don't see any reason why a RDBS ODU would not be within the OTARD limit of one meter. The higher the frequency, the shorter the wavelength, and therefore the greater the gain of a given size reflector. This is why Ka works with an 20-something inch reflector, despite having poorer propogation characteristics in atmosphere than Ku...the reflector provides more gain at Ka frequencies than it does at Ku. Unless RDBS was transmitted at lower power (under 100 watts) I don't see why it would need more gain than current dish sizes provide.
     
  11. Jun 27, 2013 #751 of 3078
    Diana C

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    In this photo of a disassembled LNB, you can see the two probes (at 0 and 270 degrees) used to recieve the two signal polarities. Why not simply add probes at 90 and 180 degrees, and tune these to RDBS frequencies?
    [​IMG]
     
  12. Jun 27, 2013 #752 of 3078
    HoTat2

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    They could;

    Those "antenna" probes included in the Ka feedhorns could then feed separate receive circuits with a L.O. to down-convert RB-1's RDBS band at 99w likely somewhere above 2150 MHz where it could be combined on trunk lines 1 and 2 with the current 99/101 even and odd signals respectively.

    And for whatever future satellite carries the RB-2 payload at 103 (possibly D15?), the Ka/Ku/RDBS LNB could place the down-converted RDBS band above 2150 MHz on trunk lines 3 and 4 along with the 103/110 (If an SL5)/119 even and 103/119 odd signals respectively.
     
  13. Jun 27, 2013 #753 of 3078
    P Smith

    P Smith Mr. FixAnything

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    This one is more advanced LNBF board :)
     

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  14. Jun 28, 2013 #754 of 3078
    harsh

    harsh Beware the Attack Basset

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    In simple terms, I think the antennae you're looking at are designed for linear polarity (horizontal and vertical) and what DISH and DIRECTV use is typically circular polarity.
     
  15. Jun 28, 2013 #755 of 3078
    harsh

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    Nor has anyone produced any examples of a single LNB that receives the bands in question. If there is one, it is certainly possible. If they need two entirely separate LNBs, the dish would need to be multifocal.
     
  16. Jun 28, 2013 #756 of 3078
    harsh

    harsh Beware the Attack Basset

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    The dish bands are adjacent in this case and of the same broadcast power. I'm pretty sure you can say that about Ku and RDBS.
    When I say antenna, I mean the antenna in the feed horn, not the whole dish. If I had been referring to the dish, I would have said dish.

    I don't think it is reasonable to compare a Ku - Ku combination to a Ku - RDBS combination as you're holding up as an example.
     
  17. Jun 28, 2013 #757 of 3078
    studechip

    studechip Godfather

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    If there is one, do you think Directv would necessarily be displaying it publicly? Why would they go through the time and expense of developing RDBS if they didn't already have a way of implementing it? Just for fun?
     
  18. Jun 28, 2013 #758 of 3078
    Diana C

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    There are still two probes...circular polarity is received the same way vertical and horizontal polarity is received, it simply eliminates the need to rotate the feed horn to align the antennas with the signal. The probes align at any point.

    In fact, with circular polarity you could theoretically mount any number of probes and do Ka, Ku and RDBS with one LNB (although you would likely lose some waveguide efficiency).
     
  19. Jun 28, 2013 #759 of 3078
    HoTat2

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    They don't have to be separate LNBs and the present Slimline dish has an "integrated" Ka/Ku LNB and its multi-focal as would be the same dish with a future Ka/Ku/RDBS integrated LNB.
     
  20. Jun 28, 2013 #760 of 3078
    HoTat2

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    From my understanding, circularly polarized LNBFs use some type of dielectric material (teflon perhaps?) inside the feedhorn that converts the CP signals into H/V linear ones for reception by linear probes at right angles like the ones DianaC posted.
     

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