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SWM transponder signal strenths question

Discussion in 'DIRECTV HD DVR/Receiver Discussion' started by gregftlaud, Aug 26, 2012.

  1. gregftlaud

    gregftlaud Hall Of Fame

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    Can someone tell me what SWM transponder signal strengths mean and if they also come from the satellites?

    Bad weather down here in ft lauderdale even in the heaviest of rains i've never seen my SWM transponder signals go below 95 but tonite it is pouring really bad and my SWM signal strengths are in the 70's (my other sats strengths much worse).

    I always thought SWM signal strenghts were determined within your setup but can low satellite readings being affected by heavy rain affect your SWM readings as well?
     
  2. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    The SWiM signals come from the LNB, so if the LNB's output is low, so will the SWiM.
     
  3. NR4P

    NR4P Dad

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    Greg, I am not too far from you in the middle of some nasty feeder bands. A few minutes ago, even the 101 SAT was all zero's and so were all the SWM channels.

    Now with the 101 back and 103/99 coming back, SWM levels are up where they should be, with a few zero's as usual.
     
  4. gregftlaud

    gregftlaud Hall Of Fame

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    OK then apparently weather and signal strengths from other sats CAN affect your SWM readings b/c my SWM signal strengths just went back up after the feeder band finally got thru...just like yours NR4P

    So looks like a part of that "LNB output" has something to do with signal strenghts the LNB is getting from 101, 103, 99 sats.......and not just dependent if the LNB is working properly or getting enough power.
     
  5. HoTat2

    HoTat2 Hall Of Fame

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    All signal strength screens including the 1-9 SWiM level one, measure the relative "Bit Error Rate" on a scale of 0-100.

    And the BER is dependent upon the C+I/N+I (sometimes abbreviated to C/N if interference is ignored ) ratio at the input of the LNB feedhorn.

    Therefore if rain fade, interference, signal blockage, etc. degrade the C+I/N+I ratio so will the numbers on the various SS screens.

    However, it has always been of interest to me what specific 8 programming transponders (ignoring the CG one which is obviously 101) are selected for the SWiM level screen. And the fact that you notice them drop out when Ku 101 goes out well after the Ka band goes down makes me wonder if they are not all from 101.
     
  6. TomCat

    TomCat Broadcast Engineer

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    It might be more likely that they are using a MER or modulation error ratio scheme, which more accurately gives a quantitative approximation of reception/demodulation, and allows that to be modeled on a simulated analog scale more easily that BER, which is simply a baseband count of corrupted bits vs non-corrupted bits. Either will work, but one works better than the other in many cases.

    MER is probably not expensive to implement here even though a bit more sophisticated, because it can utilize the demodulator already built into the tuner path just like a baseband count of bit errors can. But if MER actually is more expensive to implement, then I would guess that either BER or Eb/No becomes the desired protocol. Eb/No might even be the least expensive since it doesn't need to factor in the bandwidth.

    Technically, they could be all from 101; the "Satellite Transponder Guide" lists DirecTV 4S, 8, and 9S (listed at 101 W) as hybrid Ka/Ku sats, and they can reconfigure any number of transponders to either mode on the fly. My best guess is that they do not illuminate in Ku at all from that location, but that is only a guess based on what channels they provide.

    Even if they do not, your signal screen could still be seeing Ku signals from the 101 location (which just by nature of them being there could show up on any metering system looking at 101) because SES-1 is also at the 101 location and has 9 Ku transponders illuminated there, at least according to the Sat Guide. DISH metering turns the normally green bar red to weed out signals with a different identifier, but not all methods do that; no telling what DTV does.

    There are a couple of reasons why the Ku might fade later than Ka; one is that Ku is less susceptible to atmospheric obstacles than Ka, meaning it would naturally drop off later during an increasingly bad weather event. This makes more sense than anything else because SES-1 is a 20-watt bird, while the DirecTV birds are 120 watts, which should mean that the Ku from there would drop off before the Ka from DTV. Not sure why SES-1 is so low in power; it only went up a couple of years ago, and back then it was berthed at 131, so we may not have seen it at 101 for all that long.


    There may be level adjustments due to amplification or attenuation in the distribution from the dish, but the original signals have to come from somewhere, and they all come from the sats. The LNBF definitely amplifies this signal, and there can be amplification elsewhere in the distribution, but if the input signal goes to 0, there is nothing to amplify, meaning that the signal reading will be 0 as well. Signals are converted from band to band but none are actually generated within the antenna or distribution path, other than the return DC.

    It is possible that SWM is designed to have less vulnerability to rain fade, which may account for the higher signals (70's) but without an input signal of some measurable strength, that will also drop to 0, because we all know what happens when we multiply any number by 0. It does not matter how large that multiplier is, the result is still 0. Same in amplification; it does not matter how strong the amplifier is if the input is 0.
     
  7. HoTat2

    HoTat2 Hall Of Fame

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    Possibly;

    Without detailed knowledge of that portion of the IRD's circuitry its hard to say precisely what specific measure, BER, Eb/No, MER, etc. the receiver level meters are using as a reference, other than to say they are all a relative measure of received data error rates and not actual RF signal strength as though it were like an analog agc signal or something.

    Well DIRECTV-4S is not hybrid, but Ku only. DIRECTV-8 and 9S are with both Ku and Ka band payloads.

    Subscriber equipment can only receive the Ku signals from 101 in the broadcast portion of the Ku band between 12.2-12.7 GHz.

    The Ka band payloads on -8 and -9S are not receivable by subscribers nor can they be interchanged with transponders on Ku, and are used for signal backhauls between regional LiL aggregation points and various DIRECTV broadcast centers.

    DIRECTV equipment receives signals from 101 which fall into the broadcast ("BSS") or "DBS" portion of the Ku band between 12.2-12.7 GHz and use circular polarization.

    SES-1 is a non-broadcast commercial satellite at 101 for the Fixed Satellite Service ("FSS") operating on C and the FSS portion of the Ku band between 11.7-12.2 GHz and uses linear polarization for both.

    http://www.lyngsat.com/SES-1.html

    Have to dig up the FCC files on SES-1 to know the transmit power levels for sure, but I would assume the 20 watt figure if correct is for the C band payload, whereas the Ku band one is certainly greater.

    BTW, for the record the national beam transponders from the FCC filings;

    D4S uses two 280W, two 240W, and six 120W transponders for a total of up to 10.
    D8 uses two 113W DLCTs in parallel for 226 watts combined per transponder for 16 (odd number).
    D9S uses 3 150W DLCTs in parallel for 450W combined per transponder for up to 10.
     

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