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...
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  • 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.

pswired's avatar
pswired
Junior

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/

vladams2015's avatar
vladams2015
Sophomore
6 years ago
Chances are the LNBF is amplifying and sending L band. Impedance mismatch on L band is still a big big deal, as is signal loss through the cable.

Point being, your RG6 from your dish to your modem is not carrying simply a TX/RX, so dielectric grease impacting impedence (especially with 75ohm systems) and signal loss transmit power gain will (in most cases) severely degrade a system design to transmit at 25/3

Thanks for your research though. Always looking for new info in my world!