DIY Home Improvement Forum banner

How to check cable signal strength

7K views 34 replies 9 participants last post by  Tonglebeak 
#1 ·
Hi all --

I just spent an hour in hour crawl space and was able to reconnect a long unused coax/cable outlet to my Comcast input.

However, the coax cable was slightly rusty at the end (it had been sitting loose under the house and the cable appears to be 15-20 yrs old. I would just put in a new cable, but the wiring was really tight and would be a pain to re-fish.

Miraculously, the picture came in fine on my TV, but flipping my TV input back and forth between this outlet and a newer outlet, I sense a subtle decrease in picture quality. But it may just be my mind! So my questions are:

1) Is it possible that an older, slightly rustier cable provide a worsened signal?

2) Is there any way to test this on a DIY basis?

Thanks!
--Inept Cabler
 
#2 ·
1) Is it possible that an older, slightly rustier cable provide a worsened signal?
Not only possible, but highly likely.

2) Is there any way to test this on a DIY basis?
Yes, but the meter will cost $200 or more.

Common causes of strength loss are longer runs than necessary (excess cable coiled up), un-necessary connections in cable, corroded connections, and splitters.
 
#5 ·
If your cable is showing signs of rust, it is Copper Clad Steel. It needs to be steel core. As for checking signals, you can either use your Cable modem, or the diagnostics screen for your DVR or Set Top box or DTA.

Personally I would call Comcast in about the issue, and have them terminate new ends, on all new runs of Solid Core Copper wire. DirecTV uses this http://www.amazon.com/Perfect-Visio...8&qid=1385333554&sr=8-13&keywords=directv+rg6

When you pull it, do a home run to a Utility room, along with two runs min. of Cat-5e from each location. Run two runs of RG-6 to the outside, where the coax will enter the building. Also make sure that it is properly grounded to the ground rod, when you have Comcast come in and put on the fittings.

Now of course you could do the fittings yourself, but they have the testing equipment to check for proper signals, when they are done putting the fittings on.
 
#6 ·
Hey folks -- thanks so much for these answers, which confirm how little I know about wiring.

I looked up RG59 vs RG6 and I couldn't tell which one I have. The cable is actually a twin cable with two coaxes attached together. I'm only using one. The house (which I am renting) is also wired for DirectTV which I don't use, so I may be able to repurpose one of of those cables if they are state of the art RG6s.

That's great advice about using the cable box to check the signal. Looks like a little internet digging will show me how to do this.

The advice from Greg:
When you pull it, do a home run to a Utility room, along with two runs min. of Cat-5e from each location. Run two runs of RG-6 to the outside, where the coax will enter the building. Also make sure that it is properly grounded to the ground rod, when you have Comcast come in and put on the fittings."
is fascinating, but is beyond my paygrade. Is this "to code" installation, or a way to test signals?

Overall, it sounds like this is worth a $50 visit from Comcast, if only to learn what the heck is going on here.

Many thanks!!
 
#7 ·
Let me in on this since this is what I do for a living.

1) don't use solid copper. Use copper clad. Three reasons are cost, strength, and the skin effect.

2) in almost all cases, 59 cable is fine. The problem people run into is poor shielding but some brands of 6 are pretty bad as well. As long as there is a layer of foil and a good lawyer of braid, you're fine.

3) are you looking at digital channels? If so then you're either getting the same quality that leaves headend or you receive nothing at all. You also don't want to compare SD to HD.

4) the cable you describe is ran by satellite companies typically. Twin pair.

5) a corroded fitting changes impedance which does affect signal. Changing fittings are a very common fix to most problems.
 
#14 ·
The reason they change the fittings on connections, is due to using Copper Clad Steel, and that there are tech's that do not know how to terminate them properly.

As for skin effect, it has nothing to do whether the cable is CCS or solid Copper core. Also RG-59 is only good for short distance patch cords, not for long runs through homes, also never ran from the pedestals or poles to the structure.
 
#9 ·
Here is a good blurb on it....

To summarize....RG59 would actually work as well or better for an antenna feed (less loss). But for Satellite...RG6 is better.....though, RG59 will also work.

I agree that replacing the connectors would most likely solve any 'rust' issues....but....you need the right connectors.....and I have not been happy with the garbage that HD or Radio Sh!t carries.....in the twist on flavors....

Now, if you have a coax crimper....that is the good way to go.

http://www.milestek.com/blog/index.php/2009/09/rg59-coax-vs-rg6-coax/

The first obvious difference between RG59 and RG6 is the diameter of the cables themselves. Standard RG59 coax has a 20 AWG copper center conductor and RG6 coax has an larger 18 AWG copper center conductor, offering higher bandwidth and longer distance capability.

Generally, RG6 is widely used in CATV and Satellite DSS applications and RG59 is used for in analog CCTV or baseband video applications. RG6 Dual or Quad Shield shouldn’t be utilized for baseband applications, such as video projectors, component video, plasma TV’s, etc. It may sound like a great solution because of all the layers of shielding, but RG6 Dual and Quad Shield don’t have the proper type of shielding for the above described applications. It is manufactured using foil shields and braided aluminum shields. The makeup of the shields differs between models. The effective range of operation for foil shields is above 50MHz, which makes them perfect for rejection of radio frequency interference, or RFI, that may have an effect on satellite or cable installations. At frequencies below 50 MHz, however, foil shields are not effective. The braiding on the RG6 Dual shield and the RG6 Quad shield doesn’t have enough coverage to work effectively with baseband applications.

The frequencies that are used in High Definition are usually around 37 MHz. For those lower frequencies, an RG59 with a 95% all-copper shield is designed to block RFI inclusion at base band frequencies. Because RG59 does not have a foil shield, it shouldn’t be utilized for satellite feeds or cable feeds.

RG59 has a little less signal reduction, or attenuation, over 100 feet. The shielding on RG59 does not work quite as well to maintain Gigahertz level signals inside of the center conductor. RG6 has a better design for maintaining the signal levels inside the center conductor. This is the reason RG6 has become the standard for broadband CATV and satellite systems. A basic rule of thumb is to use RG6 for any Rapid Frequencies, and use RG59 for video frequencies. RG6 has an aluminum braid and an aluminum shield. RG59 comes with a copper braid, and in some instances, an aluminum braid and shield, although this is quite rare.
 
#12 ·
That quote is off a lot. HD can be ran 55mhz and higher. The return path is 5-42mhz, so you're obviously not going to put a forward signal in the return. That quote also generalizes the shielding of 59 incorrectly. Most 59 I come across is aluminum foil and aluminum braid. The real old 59 only comes with copper braid. That is the type that loses a hell of a lot on the high frequencies. Braid=low freq shielding and foil=high freq shielding. It still needs to be at least 60% braid coverage though so keep that in mind.
 
#10 ·
Better attenuation and more durable. With that said, if the shielding is correct, then you generally leave it alone inside the house. The exception is the drop due to distance. The only time you'll benefit from changing existing 59 to 6 is if you're already running on the edge with signal or if its defective. If it's a signal thing, it is much simpler to do what I'm already supposed to do and make sure the levels are fine out of the tap and making sure the drop isn't excessively attenuating. Last resort is a house amp. Most 59 in my area is behind walls and we do not work in those spaces. If the wire is defective then obviously the only fix is to run a new one either through an exposed basement or along the exterior.

I guess what I'm saying is that its pointless to replace 59 (in house) unless it actually is causing a problem. New work should be 6 of course just for the added cushion, but ripping walls apart to replace good 59, that is causing no problems, makes no sense.

FWIW we run MOCA over 59 prewire with no ill effects.
 
#15 ·
As stated, Your Cable Modem and/or DVR or STB diagnostics menu can be used to determine signal strength. As for the tech fee, some techs may wave it, depending on the circumstances. If you have an older box, they may wave the fee for installing it, due to have line quality issues.

Same goes with if you have digital phone through Comcast, they will usually wave the fee, if having service issues with that.

Now over your pay grade, would be asking you to build a computer, to install Smooth wall, just so you can see the modem stats on a graph.

A third party that has UVerse, designed a software program for those users, to help diagnose their problems, but as far as I know, no-one has done the same at least like U-Verse Realtime, for the CATV EMTs & cable modems, so you are left doing it with the equipment, not software that you can run on your computer.
 
#18 ·
I don't care if you emit RF out of your nose. Neither of those three links really helped you out. You also don't seem to understand that RF is not AC. RF flows along the skin of CCS much more readily because, surprise, the copper is the most conductive and is on the skin of the steel core..

When you lose 6.5db@750mhz per 100ft on 59, and 5.5db on 6, are you really trying to say that it's a big deal? Especially when we're talking residential. We're not talking about running miles of this stuff. Whether or not the signal is digital or analog does not matter either. If the shielding is good, then there's no worries. Just how much do you know about qam?
 
#20 ·
It is called an example. In my area, Comcast also requires that solid core Copper is used, not CCS. I can tell that either you have not been around this stuff very long, or not very understanding why Solid Core is used, along with RG-6 by all providers, that care about their plant, and not having repeat calls, regarding line problems.

Copper Clad Steel is the worse invention ever made. It was done for cost savings by manufacturers, but in the end it causes more issues with Digital Signal transmission, for not only TV, but also Internet.

And yes those links do back up what I am stating, but it is obvious that you either never read them, or cannot understand the mathematics, along with Scientific information in them.
 
#22 ·
Excluding myself from any CCS debate :)

rg59 vs rg6, it's .77dB vs .57 dB loss per 100ft. Once you have already split a digital signal a couple of times, those dBs lost thru the cable itself start to matter.

I have used my cable modem to check strength on different cable outlets. my motorola SBG6580 will show for each of the 12 channels the SNR, and the power required for the 4 upstream channels. Rudimentary line meter.

with digital signals, db loss matters. a long run, especially with rg-59 can result in enough signal loss that not enough data is getting to the tv - causing pixilation or blanking screens. also how you split the signal matters.
from the service feed,
put on a 2 way splitter feeding the modem and then a 2nd line going into another splitter (2,3,4 no more splits than necessary). Some splitters split the signal equally, some split where one leg has less db loss - you'd use it to feed your longest run.

Just helping out friends, I've seen some horribly thought out splitting 'strategies' like the cable modem being behind 2-3 splitters. The typical 'my internet keeps going out' plea for help

Definitely would replace rg59. My home had plenty of it but replaced now. I ran big box quad with compression connectors. Big box 'quality' quad may be more marketing fluff than much better than dual shielded. ??
 
#23 ·
As you said, the setup with splitters is the biggest issue. I'd love to see a house where 100 ft home runs are being ran. most are less than less than that and the 59 is fine so long as it's aluminum foiled and 60% braided. If that extra db of loss is killing you then you're already on the border and need to fix the issue before that run.
 
#24 ·
I also want to point out that in a lot of systems, putting a modem right off the first split is now outdated. With more devices relying on a return now, you need to balance the signal pretty evenly. Our DCXs will go into disconnect status if it can't get a return, so no more two ways straight to modems.
 
#25 · (Edited)
Come on boys....behave....

First off....when quoting specs on cable...you have to say who the manuf is.....

Case in point...using Belden...@ 750 Mhz....RG6 has 5.5dB of loss/100'....RG59 9.7. But Extron brand is 6.5 for RG59.

Of course, the average person has no idea what dB is...much less the fact that 3dB is half the power or twice the power....

And I doubt anyone has any idea of what the incoming level is of their digital or analog signal is into their house.

In regards to Digital vs analog....sorry....but....a 200 Mhz digital signal is not really any different than an analog signal at 200 Mhz....except one is square (more or less) and the other is not. I'll save you the boredom of square wave infinite harmonics....

And lets not forget....coax is not the only way to transmit RF....Wave guides....rectangular tubes who's width and height is a function of wavelength. (or, the memories of tuning 10kw klystron's with wave guides)

What really matters....RG6 or RG59....the quality of the connection....

You can have the best coax in the world...but if you don't terminate it properly...then you get crap.

The center conductor is easy...the center wire (SC or CCS) sticks through the connector...hard to screw that up....most people screw up the shield....

And spare me the discussions of copper having lower resistance than steel....at RF frequencies, the characteristic impedance is not really effected by steel vs copper. The main reason copper is used is because it does not 'rust' like steel does. Your not passing any large amounts of current through it so any voltage drop is not an issue. Copper is used because it does not oxidize like steel or other metals do.

If you look at the conductivity chart....Silver is ahead of copper....further down is Gold and AL....Gold and AL are pretty much neck and neck....but we know the issue with AL....oxidation....gold is frequently used for contacts because of it's low oxidation factor as compared to copper.

So...at the end of the day....it's really a function of mechanical connections....how good are your connectors?

RG59 vs RG6? In most homes...you can't tell the difference...RG6 is better....but if the R59 has been in there a long time....and there are issues....at least replace the connectors.

edit...forgot to add....one issue related to Satellite....the antenna...the LNB might use DC for switching....(hence, the dual coax)....so....DC loss in R59 would be an issue as compared to RG6 which uses SC.
 
#26 ·
Come on boys....behave....

First off....when quoting specs on cable...you have to say who the manuf is.....

Case in point...using Belden...@ 750 Mhz....RG6 has 5.5dB of loss/100'....RG59 9.7. But Extron brand is 6.5 for RG59.

Of course, the average person has no idea what dB is...much less the fact that 3dB is half the power or twice the power....

And I doubt anyone has any idea of what the incoming level is of their digital or analog signal is into their house.

In regards to Digital vs analog....sorry....but....a 200 Mhz digital signal is not really any different than an analog signal at 200 Mhz....except one is square (more or less) and the other is not. I'll save you the boredom of square wave infinite harmonics....

And lets not forget....coax is not the only way to transmit RF....Wave guides....rectangular tubes who's width and height is a function of wavelength. (or, the memories of tuning 10kw klystron's with wave guides)

What really matters....RG6 or RG59....the quality of the connection....

You can have the best coax in the world...but if you don't terminate it properly...then you get crap.

The center conductor is easy...the center wire (SC or CCS) sticks through the connector...hard to screw that up....most people screw up the shield....

And spare me the discussions of copper having lower resistance than steel....at RF frequencies, the characteristic impedance is not really effected by steel vs copper. The main reason copper is used is because it does not 'rust' like steel does. Your not passing any large amounts of current through it so any voltage drop is not an issue. Copper is used because it does not oxidize like steel or other metals do.

If you look at the conductivity chart....Silver is ahead of copper....further down is Gold and AL....Gold and AL are pretty much neck and neck....but we know the issue with AL....oxidation....gold is frequently used for contacts because of it's low oxidation factor as compared to copper.

So...at the end of the day....it's really a function of mechanical connections....how good are your connectors?

RG59 vs RG6? In most homes...you can't tell the difference...RG6 is better....but if the R59 has been in there a long time....and there are issues....at least replace the connectors.
You're mostly right. Copper does corrode though. That's why compression fittings are used instead of crimps. The center conductor will turn green or black or whatever and destroy the low end. Impedance mismatching is bad. Leads to reflections and other fun stuff. But yes, changing the fittings is the first step in troubleshooting cable (after checking signal)
 
#30 ·
my signal loss numbers were way off.. must have been the loss at a lower frequency. rg59 specs 2.5dB loss at 50mhz (lowest vhf) and rg6 is 1.5dB... and at the highest uhf channel, is several dB in difference between the two.

and I was thinking recabling my home in terms of OTA frequencies and improving the line to my cable modem. and future proofing because in a few years our coax might be carrying lots more data...
 
#32 ·
OTA signal levels are so low that losses in coax are nothing compared to the mechanical connections and antenna setup. One of the biggest issues is the Balun (300 ohm to 75 ohm converter) on the antenna and the connections on the antenna itself.

If you want a good read....do a Google on "Twin Lead"....lots of interesting stuff there....I think you will be surprised at what you find out.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top