Calculating LNB Output Frequency (Project Part II)

Discussion in 'Free To Air (FTA) Discussion' started by equant, Dec 15, 2009.

  1. equant

    equant Thread Starter Active SatelliteGuys Member

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    I'm trying to figure out how to know what the LNBF output frequency is for a given transponder, and in particular what's realistically the maximum frequency I should expect.

    Using the maximum FTA downlink frequencies I could find:

    Max CBand Transponder: 4192 MHz
    Max KuBand Transponder: 12180 MHz

    ... Here are the calculations I'm doing. Anyone know if these are correct?

    (C LNB L.O.) - (Transponder) = 5150 - 4192 = 950 MHz
    (Transponder) - (Ku LNB L.O.) = 12180 - 10750 = 1430 MHz

    ... so, that means that the highest LNB output for C band comes from the lowest transponder frequency, and the highest LNB output for Ku band comes from the highest transponder frequency. Right?

    Min C Band FTA Transponder: 3706MHz

    5150 - 3706 = 1444MHz

    The reason I'm asking is because I've been reading conflicting things, and more importantly that the lnb output range is 950 - 2050, and I'd like to know what the realistic output range is. It might not make much of a difference, but if I'm going to play with the LNB output, it's nice to know my max frequency is 1.5GHz and not 2.0GHz.

    Any reason I should be worrying about 2.0GHz? Looks like 1.5GHz will be enough.

    Whew. Thanks for any help from you folks that have spent too much time with this hobby. :p
     
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  2. Anole

    Anole SatelliteGuys Guru

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    This is from memory, but . . .

    As I recall, the traditional LNB output range is 950 - 1450mhz
    All "traditional" (read: old) documentation will quote those figures (If I remembered correctly).

    Bandstacked LNBs give 950 - 2150 by outputting both vertical and horizontal signals simultaneously, but at different frequency ranges.
    I think 1650 - 2150 is the other polarity.

    Hopefully, with this info, whatever documents you are looking at will be more clear, even if I made a minor error on my numbers.
     
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  3. Tron

    Tron SatelliteGuys Family

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    I agree with Anole, the higher frequency range is to account for bandstacked LNBs. This is also why high quality cable is needed when dealing with bandstacked systems.
     
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  4. B.J.

    B.J. SatelliteGuys Family

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    The two freq relationships are:
    C-band
    LO-Freq - Downlink Freq = IF Freq
    KU-Band
    LO-Freq + Downlink Freq = IF Freq

    The LO freq for C-band is almost always 5150, but the LO freq for Ku can be 9750, 10600, 10750, or 11250, depending on which band and/or lnb type you're using.

    As mentioned above, the usual CONUS bands are 3700-4200 for C-band and 11700-12200 for Ku, and the IF that your receiver will see is in the 950-1450 band. This means that for the usual bands, 3700 corresponds to 1450, and 4200 corresponds to 950, and for KU, 11700 corresponds to 950 and 12200 corresponds to 1450. Ie for C-band the IF freqs are kind of reversed, ie the higher downlink freq gives the lower IF. But in both cases, the lowest freq you'd normally see will be 950, and with a "STANDARD" lnb, the highest freq is normally 1450.

    HOWEVER, there are some signals that you'll run into, usually signals aimed at South America or Europe, that are below 3700 on C-band. Since C-band is reversed on the IF, 3600 will show up at 1550, 3500 will show up at 1650, etc, etc. so to receive below 3700, you need a receiver that will go above 1450 on the IF. I can't remember how low those C-band freqs actually go, and I can't remember if they are linear or circular (ie if circular, you'd also need a different LNB or a teflon insert), however those are the only signals you'd need to worry about on C-band.

    ALSO however, there are situations when you might need to go above 1450 on Ku, but these instances are usually LNB dependent. For example, if you're trying to tune the 11700-12200 band with a STANDARD lnb, the IF will be in the 950-1450 band, however if you are using a "UNIVERSAL" lnbf, which has 2 LO freqs, usually one at 9750 and one at 10600, then, you'd be using the 10600 LO freq to tune this band, and the IF's you'd see at the receiver would be 1050-1550. Also, if you're looking to receive the low Ku band, which is down below 11700, you'd be using the 9750 LO freq, and to get to just below the 11700 downlink freq, you'd need your receiver to tune up to 11700-9750=1950.
    Therefore, if you're looking for frequencies BELOW 11700 with a regular FTA receiver, you'd need that receiver to go up to 1950 on the IF.

    I say "with a regular FTA receiver, because every FTA receiver I'm familiar with will NOT tune below 950, so with a STANDARD lnb, it is not possible to tune below 11700. You need a universal LNBF to tune below 11700, and that means you need a receiver that will go up to 1950. HOWEVER, if you are designing your own receiver, or using a communications receiver for some reason, and can tune below 950, then you may not need to use a universal lnbf if the freqs you're looking for aren't too far below 11700, but I don't think a standard LNB will go quite as far BELOW 950 as it goes ABOVE 1450, so I think the performance would drop when you went too far below 950.

    Anyway, in general, the lowest you'd need to go is 950, and if you're interested in either the low C-band band, or the low Ku band, then you'll need to go perhaps as high as 1950 on the IF.
     
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  5. Anole

    Anole SatelliteGuys Guru

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    B.J. brings up another point - Ku band in South America.
    I've seen some LNBs with LO frequency of 10500 or 10300 (?), so if that matters, do more research.
    If you don't care, then of course, forget it. - :rolleyes:

    And I left out the whole Universal LNB and its two LO because... I didn't care. :)
    ... and you mentioned 10750, so I thought you were concentrating on the North American satellites.
    But it was good to get it out into the light of day. - :up
     
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  6. melgarga

    melgarga Active SatelliteGuys Member

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    equant,
    I dont know if this will help, or is what you are looking for, but I did a lil' Excel sheet for cross calculating the IF vs C/Ku downlink freqs and vice versa for "popular" LO's a while back. Post 3 has the xls' for 10600 and 11250. Changing the LO "value" in the cells for another range of calculation that is not 5150,10600,10750, or 11250 is pretty straightfoward, even if you are not Excel savvy.
    I did the freq "charts" to illistrate the overlap of the C vs Ku desired freq to IF relationship. The lists of downlink freqs extend out of band for completeness. Here's the link to the thread - http://www.satelliteguys.us/fta-shack/181406-c-ku-if-frequency-calculator-converter.html

    Sounds like your embarking on another peoject.............????
     
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  7. AcWxRadar

    AcWxRadar SatelliteGuys Family
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    Equant,

    With Ku DBS and a L.O. of 11250:

    12700 - 11250 = 1450 max (bandstacked ???? I am a little confused on this.)

    With Ku FSS and a L.O. of 10600:

    12200 - 10600 = 1600 max

    With Ku FSS and a L.O. of 10750:

    12200 - 10750 = 1450 max

    RADAR
     
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    Last edited: Dec 15, 2009
  8. Iceberg

    Iceberg The No Pain Train
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    bandstacked is different. They go from 950-2150. To figure out the Horizontal frequency (if your receiver isnt blindscannable) is take the frequency and subtract from 25600. So 12676 H 20000 (highest TP in DBS) becomes 12924 and 12238 (lowest) becomes 13362.

    For KU Band its from 24600

    actually most receivers when a UNiversal is selected will scan from 950-2150 IF frequency. It will scan to 12750. In North America that area is reserved for DBS but in Europe its still KU linear

    correct

    My Pansat receivers (and older Fortec) when blind scanning will show the IF frequency and unless its set for LNB LO of 10750 it scans IF 950-2150. For a LNB LO of 10750 it scans 950-1600 for some reason

    C-Band it goes from 950-1600 so it does go down to 3550 for scanning
     
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  9. AcWxRadar

    AcWxRadar SatelliteGuys Family
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    The bandstacked stuff always eludes me. I cannot visualize how the circuitry is set up, so it leaves me kinda blank. Maybe someday it will register for me and a light will go on.

    RADAR
     
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  10. Tron

    Tron SatelliteGuys Family

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    Radar, bandstacking is great because it allows the LNB(F) to send both polarities down the same cable at the same time. No polarity switching is required. The LNB(F) just sends the vertical transponders normally and "stacks" the horizontal transponders at a higher frequency. Therefore, both polarities are always there, and the cable may be split or looped through with both polarities intact. Of course, the added complication is that the signal path must be capable of passing about 2.2 ghz instead of about 1.5, and the horizontal transponders will be at unexpected frequencies (above the normal range). A blind scan receiver will usually take care of finding them.
     
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  11. AcWxRadar

    AcWxRadar SatelliteGuys Family
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    TRON,

    I do understand the theory and its uses/applications, but what eludes me is how they are doing this inside the LNBF. The internal circuitry to get the H TPs on the higher frequency. Is there a separate internal oscillator? I have brushed into several explanations of this before, but so many descriptions were vague and incomplete or they contradicted the others. So, I never found a really accurate explanation.

    RADAR
     
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  12. B.J.

    B.J. SatelliteGuys Family

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    I can see the utility of bandstacking for the DBS band, where there isn't anything in that upper band, but it seems to me that it wouldn't be as useful for other bands. Ie it seems like you'd at least lose the capability of receiving out band, ie such as locking some transponders in the DBS band with a regular linear lnb {this could be good or bad}. But the existance of signals in the upper band would also seem to be an issue relative to interferrence, although I haven't thought that topic through. But what I was thinking, was that say you had an 11700-12200 lnb that was putting one polarity up at 12200-12700, it seems to me that if you have strong signals in that upper band, that they will leak through and interfere with the polarity that is now sharing that band. Ie, I'm skeptical that they could have a sharp enough bandpass filter to keep the upper band out of what is sent as the lower band.
    I'm sure that they probably made a serious effort to avoid such problems, but I just wonder how well it can work in practice.
     
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  13. Tron

    Tron SatelliteGuys Family

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    I'm not sure, but I believe that there are two oscillators at work in these LNBs. There are two L.O. frequencies, i.e., 5150 lower L.O. and 5750 upper L.O. on the Eagle Aspen B1SAT C-Band LNBF. Many receivers don't have a provision for bandstacked LNBs, but I've found that using either of the two L.O.s will get you the channels that are there.
     
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  14. crackt

    crackt Active SatelliteGuys Member

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    interesting read. ive seen cband freqs on lyngsat in the 3400 range (circular @ 40.5w) and ku freqs in the 10 000 range. from reading this i can see a wideband circular would be needed for the cband but what kinda lnb would translate the ku fraqs to usable IF.

    crackt out,.
     
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  15. Iceberg

    Iceberg The No Pain Train
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    most C-Band LNBF's will go from 3400-4200 so that works. I know the GeoSat C2 does. Its listed on the specs

    Also some receivers have it defaulted to those numbers too when blind scanning. Coolsat 5000 defaults to 3400-4200 with a 5150 LO Frequency. I forget if the Pansat goes that low. I know the Pansat grabs stuff in the upper 3500 through the 3600 but forget if it tries lower than say 3550
     
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