cable attenuation between receiver and modem

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I was looking at the status of my modem using the web browser. I've noticed that the cable attenuation is showing 15db. Being a technician that sounds like a lot to me...every 3 db is one-half of your received signal gone. The cable length might be about 50 feet. Would someone on your end of the circuit ask if that is a high amount of loss in this application and then get back to me. Thanks.

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Brian

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Posted 4 years ago

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jimpryde

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Brian,

I had to check my status quickly because I had forgotten what my attenuation was. I remember having a red flag on my modem status for cable resistance (5+ Ohms). My attenuation is at 9.1db. It is not in red flag status, though. With you also being a technician, you know that all cable has loss, but coax is notorious. You could have a crummy splice, a bad splitter, or it could just be crummy cable. A friend of mine had similar issues at his house. He ripped out and replaced all his cables and it made a dramatic difference in these amounts. Might be something to consider. 
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david, Champion

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I've got right at 150' of cable and my cable attenuation  is 10.5 right now and will be 9.5 sometimes. Yours sounds way high for 50'. I would check what jimpryde listed above. Mine got water in the outside connector one time.
(Edited)
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Larry Lockie

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I have been installing Sat Internet Since 2007, and I have been using Dielectric grease for almost that long. Have opened up connectors that are over five years old, and still Bright copper conductor. Well worth the extra effort.
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JEP

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Bryan - 15 dB sounds high for 50 feet of cable, but if your RxSNR is over 6,  all your modem status indicators are green and you aren't having connection problems, I would not worry about it too much.  Exede has very large signal margins built in to handle widely varying conditions due to weather, installation anomalies, less than optimal dish alignment, cable length, etc.  I also don't think the cable attenuation measurement is very accurate.  Mine has varied from 1 dB to 12 dB, although it typically runs about 8 dB.  If I reboot my modem, the attenuation will often reach a different but stable level, leading me to suspect that there is a baseline measurement of some sort that only takes place during modem boot-up.  Just guessing, but that's what I have observed.  If it really bothers you, try to verify that your coax is one from the Viasat approved list, and make sure your connectors are tight and dry.
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Jim, Champion

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I think JEP has given some good advice. I too don't believe the attenuation measurements we see are very accurate. I've seen very high attenuation during installation that would drop dramatically upon completion. There have been discussions on the forums before but we never got a conclusive answer about what ideal is. I was told by a tech support person once that a minimum attenuation is needed but he couldn't give me a number.
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Dave

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I am a ham radio operator, the loss on RG-6 is pretty high at these freq. I have on my system about 75 ft of RG-6 quad shield cable. Even thats rather lossy. My thought on this is that anything over 50ft runs should be using RG-11 cable. In fact I am going to order 100 ft this week from, The Wireman and replace the RG-6. The only thing is you have to use adapters on both ends, which causes a little loss but not enough to to hurt anything. 

Now the Rx SNR: 7.6 dB
Cable Attenuation 5.4 dB
Cable Resistance 2.0 Ohm
Rx Power: -48.0dBm
ODU Telemetry status Active
TRIA status is Tx RF Power:30.6 dBm

So we will replace the cable and I will post the difference in a reply to this post.

It's going to be interesting.

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JEP

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A couple of things to bear in mind.  If you signed the customer agreement, you agreed not to alter or modify their equipment.  The Exede system has an adequate  margin to work with RG6 lengths up to 150 feet and you are well under that. The RG6 selected from the Viasat approved list has to be better than 10dB/100ft at 2.5GHz.  The RG6 from the Viasat approved list has been 100% swept tested to support Viasat requirements.  RG-11 theoretically has lower loss than RG-6, but bought off of eBay (or any typical supplier) it has certainly not been swept, so could very conceivably have impedance bumps which will create multiple reflection points along the cable.  Steady state sine-wave loss per foot, is not the only consideration for a digital system.
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JEP

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David - Also note that the RG-11 in your link has a copper covered steel center conductor.  This will have more DC resistance (for powering the TRIA) than the RG-6 solid copper center conductor specified by Viasat.  The lower resistance of the RG-11 braid may mitigate the issue for the complete circuit, however.  Don't know...
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Jim, Champion

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I doubt if changing the cable would violate the equipment modification clause. "Equipment" includes the modem, dish and TRIA but not cable. I have always been taught that once the cable is installed in your home it is yours unless there is a specific contract saying otherwise. This often comes up when a Dish or DTV tech tries to use existing cable and the cable company wants to claim it is theirs. The laws on this probably differ from state to state but I believe this to be generally true.
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Ebal Nolom

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I don't think swapping out cable violates any laws, but since RG-11 is not on Viasat's cable list it would violate any existing warranty and the result would be an unapproved installation that would fail an installation audit.  Still, probably no big deal.  There is no question that RG11 composed of the same materials as RG6 would provide less loss, but it is not clear what the practical advantage would be. The amplification built into the TRIA, on receive, is already designed to overcome the RG6 cable loss, making the advantage gained by RG11 negligible.
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Dave

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I went to http://www.3starinc.com/  I bought 75 ft RG11, It came in this morning. I like a dummy didn't check it for shorts and open connections before I Installed it.  Well guess what. I checked the center wire and found it was open. I called them and what a bunch of nice people. 
The owner is sending me a new cable and a return auth, He apologized several times for the problem. I tell ya you can't beat the customer service there. 
So looks like I will have to wait for the other cable to come. I could replace the connector but I don't have any of those for RG11. And one other thing, these connectors they put on are top-notch...
L8ter Dave

OK I did the swap and here it is.

I replaced my rg-6 cable from dish to the house with rg-11 quad shield cable, and here are the results.
I was hoping to make a bigger difference on the system, but it don't seem to have been worth the money.

Before;
SNR: 7.6 dB
Cable Attenuation 5.4 dB
Cable Resistance 2.0 Ohm
Rx Power: -48.0dBm
ODU Telemetry status Active
TRIA status is Tx RF Power:30.6 dBm

After:
Rx Power: -43.9dBm
Cable Attenuation5.5 dB
Cable Resistance1.5Ohm
Rx SNR: 8.0dB
ODU Telemetry status Active 
Tria Status is Tx RF Power: 30.6 dBm


Any input on this is always welcome.

Dave
(Edited)
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Brian

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HAM here too. I didn't bother to look up the loss of RG6 but I will. It will be interesting to see what you come up with as far as loss with the RG11.   Do you happen to know what the IF freq is from the LNA? Hardline is next! lol!
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Ebal Nolom

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Specs for the TRIA say, TX-IF: 1.8-2.3 GHz and RX-IF:0.8-1.5 GHz.

RX and TX chains both have roughly 55dB of gain in the TRIA which tends to dwarf the thermal noise introduced by coax loss.

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Brian

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http://www.w4rp.com/ref/coax.html

Some good figures here.
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Exede Beau

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Brian, these guys have given tons of good information, hopefully it has helped. I would like to take a look internally though and see how everything looks. Please send me your account information at exedelistens@viasat.com and I will take a look.
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Brian

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I'll do that when I get home this evening. I'd had some seemingly slow speeds and when I looked at the TRIA/Modem stats and saw the high value for loss I was curious. Probably nothing to worry about if the gain through the chain is indeed at 55dbm. 14db of loss just looks high. I'll touch base with you later today. Thanks.
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Exede Beau

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Thanks for your email, Brian. Glad I was able to find some information for you. If anything else comes up, please let us know.

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