Forum Discussion

gaines_wright's avatar
gaines_wright
Tutor
6 years ago

Warning, don't fry your modem.

  Some years ago, an EMT vehicle backed over and destroyed my Hughes dish. The next morning I called my trusty tech company, and the first thing he asked me was if the coax was damaged, and next if h...
Performance
  • BirdDog's avatar
    BirdDog
    6 years ago

    Yes, there is DC power supplied by the modem going through the coax to power the radio on the dish. Under certain situations the modem can be damaged if the power is shorted out. There are protections built in but they don't always work.

     

    Also one reason we say to power down the modem from the wall receptacle, not the plug on the back of the modem.

GabeU's avatar
GabeU
Distinguished Professor IV
6 years ago

gaines_wright 

 

I remember a post from a year or two ago in which someone's modem was fried due to corrosion in/on one of the connectors and water getting inside the cable and shorting the system out.  If I remember correctly it was on an older legacy installation.  I think they may have had to replace the radio, as well, though I may be conflating that with something else.  It was most likely from an insufficient amount of dielectric grease being applied to the connector or the installation tech just forgetting to do so.  Zap!  

  • vladams2015's avatar
    vladams2015
    Sophomore
    6 years ago
    GabeU wrote:

    gaines_wright 

     

      It was most likely from an insufficient amount of dielectric grease being applied to the connector or the installation tech just forgetting to do so.  Zap!  

     

    Just a tidbit of information, while typical coax connectors are not IP rated, the application of an additional dielectric will change impedence and negatively impact throughput, as the cable, connectors, transceiver, and receiver are all designed to be impedence-matched. Just an interesting thought to consider. Which is more important? Ingress protection, or maintaining transmit power and throughput without any significant loss or gain (depending on how you look at it)

     

    • GabeU's avatar
      GabeU
      Distinguished Professor IV
      6 years ago
      vladams2015 wrote:

      Just a tidbit of information, while typical coax connectors are not IP rated, the application of an additional dielectric will change impedence and negatively impact throughput, as the cable, connectors, transceiver, and receiver are all designed to be impedence-matched. Just an interesting thought to consider. Which is more important? Ingress protection, or maintaining transmit power and throughput without any significant loss or gain (depending on how you look at it)

      The connector in question was likely not weather sealed properly, as well.

      • vladams2015's avatar
        vladams2015
        Sophomore
        6 years ago

        obviously so, however the point is that a type F connector (while not IP rated per se) are standard IP64 and applying a dielectric is poor practice...but one is left to consider: do we care more about a cable being submersible, or about ensuring an impedence match. 

    • gaines_wright's avatar
      gaines_wright
      Tutor
      6 years ago
      vladams2015 wrote:

      Just a tidbit of information, while typical coax connectors are not IP rated, the application of an additional dielectric will change impedence and negatively impact throughput, as the cable, connectors, transceiver, and receiver are all designed to be impedence-matched...........

       

         In this case the coax was actually cut in two, so the connector wasn't a factor.

       

        It's been over 30 years siince I worked with coax ( I didn't enjoy the experience ).  I don't remember using any sort of grease on the connectors.   We eventually replaced all  the coax in the plant with fiber optics.  Which is about the only thing that will work in a central Florida phosphate plant   We all celebrated when the last piece of coax was gone. 

       

       

      • vladams2015's avatar
        vladams2015
        Sophomore
        6 years ago

         

         I don't remember using any sort of grease on the connectors.   

         

        There is still a going trend to use dielectric grease in outdoor applications of F-type connectors, and for whatever reason some companies insist on it being appropriate. When you run 100 ft of RG6 with a dielectric in the connector on the main connection, and all four connections in the loop, and don't expect significant loss...you are being naive at best. Companies like HughesNet, Viasat/Exede, etc should use LMR400 as a baseline, with N-type connectors, and certainly no dielectric. Techs often overlook (or don't understand) how a dielectric grease will impact impedence in the connector. We rely on internal dielectrics in the cables to maintain a matched impedence and minimize signal loss and transmit power gain...yet we make it common place to impact impedences and increase the loss/gain while using a (sure its solid copper core) cable that has its own inherent signal loss issues regardless of impedence matching.

         

        It is truly a shameful practice in the RF world. If HN can't pinpoint problems with my system, I will be building an LMR400 cable from the dish to the modem, removing dielectrics, and changing all connectors to N-type and see what happens. Guarantee my speed will increase and transmit power will decrease. There are a lot of factors at play that should be customizable in these systems, but alas it is a cookie cutter product that is meant to work for Joe in the inner city with a 20 ft cable run, and Susie in the farmland with a 100 ft run. 

        Not to mention HN installers do not care about both horizontal and vertical distances between the modem and the dish. Feedback, resonance, and crosstalk is a thing.