Coax Cable as a basic component (1 Viewer)

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zamar23

SatelliteGuys Pro
Feb 5, 2009
1,204
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Mid West
Coax Cable Resistance

Quality coax cable is critical for weaker sat signal reception. Below is given excerpt from Coaxial Cable - An Overview (click Tech Info - Coaxial Cable) - the article written in simple terms by an experienced Sat Installer. This article section compares RG59 to RG6 cable, and offers his method to calculate max cable length still allowing to control switching sat components.

"That brings us to the point of comparing RG6 vs. RG59

In the old houses we still can meet homeruns made by RG59 cables.

RG59 is a lower grade of coaxial cable than RG6, consisting of a smaller center conductor, a smaller insulating dielectric, and a single outer shield. However, it delivers acceptable performance for CATV. RG-59 has a 22 AWG center conductor.

RG6, on the other hand, has a larger center conductor (18 AWG), a dual or quad shield (2 braids and 2 foils), and a much larger insulating dielectric.

The benefits of using RG6 cable include: more bandwidth, lower susceptibility to interference, and lower attenuation per foot. All of these characteristics allow it to handle a higher bandwidth than RG59 cable. RG6 delivers exceptional performance for CATV, satellite, and all other video applications and is considered the cable of choice for digital TV.

Length of cable

RG59 has electrical ‘voltage drop per foot’ to a direct current 0.06 V.

RG6 has electrical ‘voltage drop per foot’ to a direct current 0.04 V. (see the characteristics of the cables)

Voltage drop depends on resistance of the cable. Encyclopedia of Physics states that resistanceof a long cylinder or wire is given by:

R=?× L/A,

where L is a length; A is a cross section area or diameter; ? – resistivity of the material.( Ohm/meter)

That is determines maximum length of cable between LNB and receiver (power source in that case) 125 feet.

125 feet × 0.04V/foot = 5 volts. (difference between 13V and 18V)

Technically since everything has a tolerance so that LNB seems to switch to the Left hand polarization even with lower voltage."



Question:

One question seems obvious from the above calculation is that if one's coax cable length exceeds 100 - 125 ft, he would need to use a powered switch to supply stabilized power to the LNBs independently of the receiver. The switch itself would need to be located no further than 100 ft from both the receiver and each LNB. Is that calculation correct?

Anyone has experience in running longer than 125 ft cables and having no problems with LBN polarity control? What kind of cable worked best for you?
 

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Mr Tony

SatelliteGuys Pro
Supporting Founder
Nov 17, 2003
295
43
Mankato, MN
my 2nd motorized (36" GeoSatPro dish, SG2100 motor with WSI LNB hooked to Coolsat 5000) is approx 140 feet. I dont know the exact length but it is at least 125-130 feet and I have no issues. Signals are nice and strong and it picks up the weak feeds that the 30" motorized setup sometimes can't (and that run is only 40 feet)

oh and there is a coupler in the mix too. Cable comes off the roof about 30 feet into the basement and coupled to the 100-110 foot cable that runs through the basement, through the laundry room, into the garage and then up into the computer room. Dont know the exact length since it was from a 500 foot box

Yeah I could run a straight shot cable but that is a helluva lot of work the way my house is set up to rerun a new cable ;) (and since it aint broke I'm leaving it alone) :)

edit: its all RG6 from Lowes swept to 3GHz
 
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pendragon

SatelliteGuys Pro
Oct 13, 2008
1,100
63
zamar: You are saying that coax cable of a given type has a constant DC voltage drop per unit length, which absolutely is not true. Look up Ohm's Law. A given length of coax cable will have a resistance which when multiplied by the current will give the voltage drop. If the current is zero, the voltage drop will be zero. The more current a LNB draws, the greater the voltage drop.

However LNBs don't draw a lot of current, so cable length rarely causes polarization switching problems in FTA. One normally runs into signal attenuation and tilt issues long before.
 

B.J.

SatelliteGuys Pro
Oct 15, 2008
2,029
1
Western Maine
ZAMAR:
Another example of don't believe everything you read on the internet.
The voltage drop will depend upon the load out at the dish, and it will also depend upon voltage applied, or expressed another way, it depends on the current you're running through the cable. If you have a high impedance load out at the dish and aren't drawing much current, you won't see much in the way of voltage drop at all, no matter what cable or cable length you use. I have more than 250' of cable, and if I put a voltmeter out at the dish, it's still going to tell me that I have ~ 18V out there. Of course, if you're drawing any significant current, then yes, you're going to have a significant voltage drop, but lnbfs have pretty low current drains, usually less than 1/10th amp. You may have problems powering motors with long cable runs, or RG59 though.

Re RG-59, while yes, it is cheaper cable, and you'll tend to lose weaker signals, particularly at the high end of the Ku band, or low end of the C-band, I used to have a 175' cable run, but moved the location of my receivers, and all I had available was about 75' of RG-59, which I spliced in to make up my 250' run. I don't think I lost a single channel that I normally watched. I'm sure that there were some weaker ones affected, but I never noticed losing any. And when I finally upgraded, and ran the whole 250' with RG6, I didn't notice much difference either.

Actually, I should clarify that yes, there was a difference, particularly in that I could see signal strength drop off at the higher IF freqs, but S/N wasn't affected that much, because the noise was attenutated too.

Anyway, while I certainly don't recommend RG59, and wouldn't use it again, except as a temporary measure, and yes there is going to be signal loss, it's not nearly as bad as you'd think from it's reputation (lack thereof). As in many aspects of this hobby, I think that a lot of people make a big deal out of specs that look important on paper, but when it comes to the important spec, ie can you lock transponders and watch TV, it's not that important.

And back to the question of powering switches, etc, no, I've never had a problem. And yet, from your statement above, you'd think 250*0.04 would drop me down 10V down to 8V. Obviously not happening.

Bottom line, I think you have to be careful about how you interpret things on the internet, even if they are factual.
That being said though, don't put much faith in what I say either. Especially during happy hour. :)

EDIT: I see it took me so long to type this that you got another response.
 
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Cadsulfide

SatelliteGuys Pro
Sep 8, 2008
1,305
0
Cavalier, North Dakota
I'm 125' or better from the dish array and have no trouble with either voltage switched or bandstacked lnb's. I even drive a couple of DP34's (power hungry) at the end of the cable with no issues. I am using RG6 cable rated for 2250 mhz, RG59 is not rated for satellite service. RG59 is fine for baseband distribution AFTER the reciever, and in many cases it is easier to use the existing RG59 than to tear up the house running new RG6. Many houses are wired with RG59 daisy chained (a real headache) rather than home run-ed. At $50-$75 per home run installed, a lot of folks will balk at rewiring 8-10 cable outlets. I use it all the time for carrying video from camera's, it is way cheaper than RG6.

As Pendragon pointed out, it is not so much the I*2R losses as the poor frequency response of the cable that will give you grief. That being said, poor connections, unnecessary splices and cheap components will undo any gains made from using good cable.
 

zamar23

SatelliteGuys Pro
Feb 5, 2009
1,204
1
Mid West
Thank you, guys! Valuable input.

You are saying that coax cable of a given type has a constant DC voltage drop per unit length.
Did I say that? I said it was a calculation of an experienced installer. :D

Nonetheless, this thread explains quite important topic of voltage and signal drop in coax cable in a great detail. In fact, we just started exploring experience of this gentlemen, and it was my pleasure to introduce him here. He has a lot more to say about coaxial cable. Please be gentle, you know I'm new :eek:. But he's experienced and certified. In fact, he runs Installation Training Courses, and was a DN & DTV Service Supervisor. ;)
 
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pendragon

SatelliteGuys Pro
Oct 13, 2008
1,100
63
Did I say that? I said it was a calculation of an experienced installer. :D

Nonetheless, this thread explains quite important topic of voltage and signal drop in coax cable in a great detail. In fact, we just started exploring experience of that installer, and I'll take the risk of representing him here. He has a lot more to say about coaxial cable. Please be gentle, I'm new :eek:. But he's experienced and certified. In fact, he runs Installation Training Courses, and was a DN & DTV Service Supervisor. ;)

I'm not trying to impugn anything about your newly found friend on the Internet. Within its context, the quote is simply factually wrong. Any high school physics student should be able to cite V = IR. If I = 0, then the voltage drop V = 0. End of story, or QED by counterexample.
 

zamar23

SatelliteGuys Pro
Feb 5, 2009
1,204
1
Mid West
Be careful - my new buddy may decide to join our party and give a physics lesson... ;) I didn't have a chance to finish high school... so thanks to him trying to catch up now. Anyway, because if his article SatGuys' visitors now have a chance to learn a lot more about coax cable. :)

Don't put much faith in what I say either. Especially during happy hour. :)
B.J.

What's your happy hour? ;)

How did you manage to splice 75' of RG-59 to make up the 250' run?
 
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B.J.

SatelliteGuys Pro
Oct 15, 2008
2,029
1
Western Maine
.....
...

How did you manage to splice 75' of RG-59 to make up the 250' run?

Just regular barrel connectors or whatever they're called, ie female to female F connectors. My receivers used to be on my 2nd floor, and the coax went underground to my garage, then to the 2nd story of the garage, across to the 2nd story of the house to the receivers. Then I relocated the receivers to the basement, so I had to connect a new length of coax to where the receivers used to be, then run it down next to pipes all the way to the basement and across to the other side of the house.
 

Cham

VE4GLS
Pub Member / Supporter
Dec 19, 2008
2,393
962
Boonies
Remember RG-59 is mostly used for HF and VHF (less than 200 MHz), such as CB radio and matching networks for VHF antenna systems. Although the loss at 1500MHz IF might be acceptable, the shielding is very leaky and you might be picking up lots of electrical noise, Wifi, and other interference messing with the S/N ratio at the receiver. That's where good "quality" RG-6 has the advantage.

I wouldn't think DC losses would be much different on RG59 than RG6, at least concerning the low amperage required to run an LNBf or even a motor. Most of the loss would be in the connectors (copper tends to corrode) . N, BNC, and TNC connectors for 75 ohm systems are best because they use silver or gold contacts that don't corrode as badly but they are expensive and difficult to install... and so the TVRO standard has been F connectors for a long time now.

If really long runs are required consider some RG-11. Often you can find some at your local cable company (spool ends). It requires special F connectors to fit the larger diameter cable though.

Only my 1.5 cents...
-C.
 

classicsat

SatelliteGuys Pro
Nov 28, 2009
195
0
Ontario, Canada
That is RG 58 use for HF/VHF two-2ay commuinications (and formerly 10b2 ethernet, remember that). RG59 is the older 75 ohm TV coax used in the 70s and 80s for cable TV and antenna. They have a #22 center conductor, while RG6 has #18, so the RG59 will drop voltage at some length.
 

rv1pop

SatelliteGuys Pro
That is RG 58 use for HF/VHF two-2ay commuinications (and formerly 10b2 ethernet, remember that). RG59 is the older 75 ohm TV coax used in the 70s and 80s for cable TV and antenna. They have a #22 center conductor, while RG6 has #18, so the RG59 will drop voltage at some length.

Ah, come on, now! RG-59 was used to the CB in-duh-stry for most of their hook ups also. Our ethernet for the telephone answering service was also RG59 -- we had over 5000 feet with BNC connectors.
 
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AcWxRadar

SatelliteGuys Pro
Apr 26, 2006
4,575
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40 miles NW of Omaha. Omaha?
The proper cable is important. RG6 of any type is generally acceptable. RG59 may produce losses at high frequencies. DC current wise, RG-59 and RG-6 are roughly identical. And I do stress "roughly". The construction of each cable type may make a large difference in this regard. The type of center conductor can make a notable difference. If you are drawing high current, a solid copper center conductor is recommended. For short runs of cable, you can get by with lesser quality copper clad conductors.

Personally, I have to locate my dish antenna a fair distance from the house in order to take advantage of the best LOS. This requires me to run about 280-300 feet of cable just to get the signal to my junction box. After the box, I need to run another 50 feet to actually come into the house and route it to my receiver.

I originally used RG-6 cable, but experienced some major line losses. There was a notable signal reduction. So I bought a 1000 foot spool of RG11 cable. WOW! What a difference.

If you have to run 100 feet of cable, RG6 is fine, if you have to run 300 feet of cable, then you should use RG11.

Sadoun sold me the connector ends that fit this RG11 cable, they are much easier to install than RG6 connectors - provided you have the correct crimpers.

In the future, all my outdoor cabling is going to be RG-11 and indoors will be RG-6.

RADAR
 

Tron

SatelliteGuys Master
May 6, 2005
6,599
33
Metro New Orleans, LA
RG-11 requires a different compression tool and different, considerably more expensive fittings. However, in cases where it is needed, it is well worth the money. Most commercial dish installations I've had the pleasure to remove (or help others to remove) have used RG-11. Most of the compression tools that will do RG-11 will also do RCA and BNC compression fittings, so that's another reason to invest in the more expensive tool.
 

zamar23

SatelliteGuys Pro
Feb 5, 2009
1,204
1
Mid West
Some members on this forum suggested to use quality trunk double line signal amps like CM-5213IFD or JVI20-TR13LA placed at each remote dish & LNB and regular RG6 cable instead of RG11. Would it be a more cost effective alternative and easier to install?

If running RG11, would it make sense to run it only to a switchboard located at the house, and run RG6 from the switchboard to the house?

What makes & models of RG6 and RG11 cable are considered the best?
 
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