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.

gaines_wright's avatar
gaines_wright
Tutor
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.

 

 

 

  • pswired's avatar
    pswired
    Junior
    6 years ago
    vladams2015 wrote:

     

     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. 

    You are going to have a much bigger problem trying to use 50 ohm LMR400 in your 75 ohm HN system than you will with some dielectric grease in your F connectors. Also keep in mind that the cabling between the modem and the dish is not carrying RF. The radio in the system is located at the antenna feedhorn and is integrated with the LNB. Signal quality as measured by the HT2000W is determined at the dish itself. 

    • gaines_wright's avatar
      gaines_wright
      Tutor
      6 years ago

      ............................. Also keep in mind that the cabling between the modem and the dish is not carrying RF. The radio in the system is located at the antenna feedhorn and is integrated with the LNB. Signal quality as measured by the HT2000W is determined at the dish itself. 

       

        Very interesting, but I'm somewhat confused ( as I often am ).  Does this mean that the coax is carrying digital data as well as the DC power for the radio, and then the radio converts it to RF?  If so, wouldn't a piece of cat 5 cable work just as well?

       

        I'm asking this because some years ago I had Mainstreet broadband, which used a small square antenna which was hooked to a modem with cat5.  I almost cried when they went out of business, $28 a month with no added taxes or fees, blazing fast, and with unlimited data.

       
    • vladams2015's avatar
      vladams2015
      Sophomore
      6 years ago
      You make one interesting yet terrible point pswired

      If I am talking about impedance matching, do you not think I would use 75 ohm LMR400? I mean justifiable concern but I can assure you I will impedence match.

      Keep in mind one other thing, seriously now...signal strength is measured at the dish itself sure. The problem with your concern is that you believe there is no chance for signal loss or transmit power gain between the modem and the dish, and for this you are sadly mistaken but understandably so.

      If there was not need for RF cable between the dish and the modem, it would be on much cheaper and extremely faster 1000/100/10 cat6e with excellent shielding metal backshells, and shields connected to the backshells, with dielectric running through the cable. My point is that you could have all of the bells and whistles in a cat 6 cable and still be cheaper than solid copper core RF. So...what’s the deal then? Why (according to you) would you use RF cable when there is no RF traveling between the LNBF and the modem?
      • pswired's avatar
        pswired
        Junior
        6 years ago

        So, I've done some more research on the HT2000W and its corresponding ODUs and found the following:

         

        -I assumed, since HN reps and installation documents routinely call the ODU a "radio" that all of the system modulation and demodulation was being performed outdoors. Apparently that's not the case, and HN is using incorrect terminology. 

         

        -It appears that the system modulation is performed in the IDU according to its datasheet: https://www.hughes.com/sites/hughes.com/files/2017-04/HT2000_H56163_HR.pdf

         

        -Since the cable between the IDU and ODU is RG6, obviously Ka band RF (25+ GHz) is not travelling across that cable. The ODU is downconverting to some IF. Hughes won't tell us what that IF is. https://community.hughesnet.com/t5/Tech-Support/Need-to-know-IF-frequency-used-between-antenna-and-modem/td-p/82886

         

        -Modern microwave systems often do have all of the RF components located in the ODU, yet still use coax to connect to the IDU, even though it's just digital data flowing between the two. Especially in residential satellite, installers are used to working with coax, and there would be additional costs and time associated with training them to work with outdoor twisted pair cabling. Also, coax conenctor ends are (in general) easier to waterproof than RJ series connectors are.

         

        So, bottom line, yes losses in the IF cable matter, but a slight impedance mismatch due to dielectric grease in a connector is not going to ruin the system margin. Here's the official doc from HN on IF cable lengths, which is telling: http://www.satelliteguys.us/xen/attachments/fsb_080202_01a_spaceway_cables-pdf.36329/

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

       

    Interesting.

     

      I worked in a phosphate plant in central Florida ( Which has more lightning than any place in the US ) that was built mostly on reclaimed land from a salt water bay.

     

      The plant had been in operation since 1915, and the combination the salt water, and years of acid spills, turned the whole place into a giant battery.  I used to joke that if you bolted a 4/0 welding cable to a beam at GTSP and then ran it to #4 CAP ( about 3/4 mile away ), you could probably weld with the ground loop current.  BTW the place was well grounded.  I was amazed to see the number of ground rods that were put in when they built a new plant.

     

      When we put in our first Distributed Control System, it was connected with coax as double token ring.  We called it the broken ring.  All of the coax had to be quickly replaced with fiber optics, which added another layer of hardware that could fail, since a FO to coax converter had to be added to each DCS site.  It was still a broken ring, it just wasn't broken as bad.

     

      We all breathed a sigh of relief when the DCS company finally supported ethernet.

     

      Boy, writing this has brought back a lot of old memories, although I worked there for 31 years it's all been 16 years ago.

     

    "If men were the automatons that behaviorists claim they are, the behaviorist psychologists could not have invented the amazing nonsense called “behaviorist psychology.” So they are wrong from scratch--as clever and as wrong as phlogiston chemists."

    Lazarus Long

     

    • vladams2015's avatar
      vladams2015
      Sophomore
      6 years ago

      Fiber and 1000Gb is definitely the way of the future. RF will always have its place, but I would rather see a company like this use quadrax or even pure silver twinax and start utilizing some aerospace tech instead of staying with the antiquated tech they still stick to because it has worked for so long.

      I understand the inherent costs, but if you can provide speeds faster than the competitors simply by using different cabling...dudes, why aren't you doing it?