# Dual Shield vs. Quad Shield RG6?



## bmoore0

So I'm about to run some wire through the house and I have the question of QS vs DS?


I've got recommendations for both Belden and Canare (which is a DS) and can't find any reason to choose one or the other - seems like QS would in general be better, but then why the recommendations for Canare?


Currently I'd just use this for analog video, but I'd like to future proof it (within reason).


What do I need to know to decide?


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## tubeguy44

there are two general rules when purchasing wire and/or cables...


1. buy cable made in the u.s. or canada (if you live in north america)


2. buy name brand cables....belden, canare, commscope.... if you've never heard of the brand name - then don't buy it...


as for dual shield versus quad shield.... the price difference is minimal.... esp if you consider the length of time that the cable will be in the wall.....

get the quad shield... it gives you the higest amount of shielding currently available.....


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## Larry Fine

Quad-shield is one of the best-known, least-understood, least-necessary things around. My local cable company uses a cheap, single-shield cable, and that's even for customers with cable-modem internet service.


Plus, for anything other than RF, RG-59 is adequate; maybe even better. It's certainly thinner, more flexible, and easier to terminate. Keep the RG-6 for RF use. (These are just my opinions, by the way.)


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## tubeguy44

Quote:

_Originally posted by Larry Fine_
*Quad-shield is one of the best-known, least-understood, least-necessary things around. My local cable company uses a cheap, single-shield cable, and that's even for customers with cable-modem internet service.
*
of course the cable company is going to use the cheapest thing that they can find..... and that's why many people have picture problems on their cable systems.....


single shield cable...whether RG6 or RG59 with a braid shield is only rated as *95% Shield* .... RG6 dual and RG6 quad shield is considered *100% shield*..... when you put the cable in the wall today you might not have any interference problems...but what happens 6 months from now when a new radio stain builds a transmitter a mile away from your house?? .... or some other situation beyond your control??


if you are putting a cable in the wall, why not put in a cable with the best shield?


additionally, if you are using coax for a satellite installation... you should definitely use RG6 quad..... RG6 quad is frequency rated up to 2.2 gigahertz... the other cables are not rated that high....


again.... to make yourself future proof as best you can.... install the best cable you can find..... the price difference is minimal when you consider the length of time the cable will be in the wall....


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## CJO

Quote:

_Originally posted by tubeguy44_
*single shield cable...whether RG6 or RG59 with a braid shield is only rated as 95% Shield .... RG6 dual and RG6 quad shield is considered 100% shield..... when you put the cable in the wall today you might not have any interference problems...but what happens 6 months from now when a new radio stain builds a transmitter a mile away from your house?? .... or some other situation beyond your control??


if you are putting a cable in the wall, why not put in a cable with the best shield?
*
This is not correct. Quad-shielding gives you less braided shielding than a 95% coverage dual-shield. The most common 60/40 braiding for quad shielding gives you only around 76% coverage.


Take a look at this article:
http://www.bluejeanscable.com/articles/shielding.htm 


CJ


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## tubeguy44

Quote:

_Originally posted by CJO_
*This is not correct. Quad-shielding gives you less braided shielding than a 95% coverage dual-shield. The most common 60/40 braiding for quad shielding gives you only around 76% coverage.


Take a look at this article:
http://www.bluejeanscable.com/articles/shielding.htm 


CJ*
the article is totally wrong about the shielding of RG6 quad....


in one paragraph it states:

*Foil offers the obvious advantage of complete coverage; it is a very easy matter to apply foil to a cable in such a way as to cover every last bit of the dielectric*


and then furthur on down it states:

*Quad-shield has two layers of braid, but these are ordinarily only 40% and 60% coverage braids (Belden 7916A, for example), yielding a net coverage of 76%*


the one fact that the article conviently overlooks is that a quad shield RG6 uses *FOUR* shields.... there are two braids and two foil shields - foil shields that provide *COMPLETE COVERAGE* (as stated above)...


so...your two braids provide 76% shield and the two foil shields each provide 100% shield....


you get the benefits of braided shield for grounding purposes and the more complete shielding of TWO 100% foil shields!!!!


it's really amazing that this RG6 quad cable which the article states is a "poor" cable is the industry standard when it comes to satellite installations and in-house cable runs....


blue jeans is just trying to sell their own "precision" cable..... big surprise!


(edited for spelling)


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## tvtech1

Quote:

RG6 quad is frequency rated up to 2.2 gigahertz... the other cables are not rated that high....
Except for the commonly available, in multiple colours, 3GHz 1505A.


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## CJO

However, also according to the article "The effectiveness of shields in intercepting noise varies with frequency, and here too, braid and foil complement each other. Braid is generally more effective at lower frequencies, while foil is more effective at higher frequencies."


They also have independent testing from Belden (who sells both quad and dual shield cable) that this is correct.


I normally would agree with you about trusting what a vendor writes. However, bluejeans cable uses commonly available manufacturers for their raw cable and are open to who they use. They also allow you to choose different manufacturers for some of their cables. I think that if there were a benefit of using quad-shielded cable over dual-shield, that they would offer that either as an option or as their only cable.


CJ


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## tubeguy44

Quote:

_Originally posted by tvtech1_
*Except for the commonly available, in multiple colours, 3GHz 1505A.*
you are correct sir!


i have not seen that particular cable locally...... how much does the Belden 1505A cost per 1000 ft spool??


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## CJO

$207.77 plus shipping at markertek.


CJ


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## KurtBJC

1505A can usually be had from a distributor for around $200.00 per thousand. Belden also sweep tests some others out to 3 GHz, including 1694A (RG-6 version of the 1505A design) and 1855A (miniature version of same). 1694A is available in ten colors; I'm not sure offhand about 1855A but think it is also. There's not much price difference between the sizes--maybe 2 cents/ft. If you're looking for a spool, I'd suggest checking with a local distributor; you can look them up at Belden's site. 1505A and 1694A are also available in 500 foot spools but only in black.


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## tubeguy44

Quote:

_Originally posted by CJO_
*However, also according to the article "The effectiveness of shields in intercepting noise varies with frequency, and here too, braid and foil complement each other. Braid is generally more effective at lower frequencies, while foil is more effective at higher frequencies."


They also have independent testing from Belden (who sells both quad and dual shield cable) that this is correct.


I normally would agree with you about trusting what a vendor writes. However, bluejeans cable uses commonly available manufacturers for their raw cable and are open to who they use. They also allow you to choose different manufacturers for some of their cables. I think that if there were a benefit of using quad-shielded cable over dual-shield, that they would offer that either as an option or as their only cable.


CJ*
i'm still interested to see how a single foil shield and one braid can be more effective at shielding than two foil shields and one or even two braids....


and the other nagging question.... why does the entire industry spec quad shield if this article is true???


why does belden (and the other companies) make a more costly cable (quad) if there were no benefits over a lower cost cable (dual)???


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## tubeguy44

Quote:

_Originally posted by KurtBJC_
*1505A can usually be had from a distributor for around $200.00 per thousand. Belden also sweep tests some others out to 3 GHz, including 1694A (RG-6 version of the 1505A design) and 1855A (miniature version of same). 1694A is available in ten colors; I'm not sure offhand about 1855A but think it is also. There's not much price difference between the sizes--maybe 2 cents/ft. If you're looking for a spool, I'd suggest checking with a local distributor; you can look them up at Belden's site. 1505A and 1694A are also available in 500 foot spools but only in black.*
about $200 per thousand......


that is obviously why normal RG6 quad sells so much better.... it usually sells for less than $100 per thousand.... and is much more available at many local outlets...


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## CJO

From what I understand, 95% coverage dual-shielded cable is actually more expensive to make than 60/40% quad shield. Also, it is very difficult to get beyond the 60/40 with quad shield and still have a cable that isn't too stiff or too hard to terminate. However, these are just things I have read somewhere and I don't have anything to back me up on that.


I wish that there was an independant audio/video magazine that would test some of these things out (and, while they were at it, do a double-blind test on speaker cables)!


CJ


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## Chu Gai

I think the answer to your question, bmoore0, lies in your asking more questions of yourself as to what you want to specifically do and what your realistic future plans are. For example, if you're looking to not only add cable for your video but perhaps looking to also want to create a whole house wiring scheme that includes computer networking, audio, telephone, etc., then you might want to consider cable bundling schemes. Better to make one single run rather than several, no? Might also increase the resale value of your home! Further, since you'll likely be running it in-wall, consideration to specifications for cable spec'd for in-wall installation is a given as is things not often thought about such as flexibility, durability with regards to abrasion resistance, etc. You may want to ponder this a bit more and once you firmly decide what your goals are, contact Canare, Belden, and others directly and ask to speak to an applications person to provide you with a list of suitable products. Color coding of cables is a pretty good idea and certainly will simplify matters when the time comes that you're wondering just where does that wire go?

As to why some people get on the Canare kick? Who knows? It's kind of like a Ford/Chevy thing in many ways.


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## KurtBJC

Quote:

_Originally posted by tubeguy44_
*i'm still interested to see how a single foil shield and one braid can be more effective at shielding than two foil shields and one or even two braids....


and the other nagging question.... why does the entire industry spec quad shield if this article is true???


why does belden (and the other companies) make a more costly cable (quad) if there were no benefits over a lower cost cable (dual)???*
Well, as you now can see, of course, the 95% braid/foil combination is actually more expensive. And to my knowledge, quad shield isn't very widely used in the broadcast industry. It's more common in CATV distribution because of its lower cost. The broadcast industry uses the precision video cables mostly because most work in post production is now done in SDI, which requires really tight impedance tolerance and wide bandwidth.


Two foil shields, in isolation, would be more effective than one. But 100% coverage from a foil shield, by itself, doesn't equate to 100% shield effectiveness. Conductivity to ground is really important, and braid coverage is important, so that 76% coverage (what you get from laying 60% down, and then covering 40% of the uncovered area with a second, 40% braid) in aluminum isn't as good as 95% in copper.


Belden's copper-centered quad shield, 7916A, is designed for DBS antenna applications. The idea is to have a reasonably well-shielded cable, at reasonable cost; it differs from conventional quad shield mostly in having a solid copper center conductor. Usually the reason for going to solid copper would be to support lower frequencies (baseband video), but in this case it's probably because of the use of DC in a DBS antenna; the less resistance in the line, the better. But the 1694A is better in every respect other than price. In most DBS applications, though, the two should perform the same, which is why the cheaper 7916A is made.


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## CJO

Quote:

_Originally posted by Chu Gai_
*IFor example, if you're looking to not only add cable for your video but perhaps looking to also want to create a whole house wiring scheme that includes computer networking, audio, telephone, etc., then you might want to consider cable bundling schemes. Better to make one single run rather than several, no?*
Running bundled cable, IMO, is much harder than doing individual runs. The cable is much less flexible and the bend radii depends on the thickness of the whole bundle, not of individual wires.


CJ


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## EmDub

When people wire up their entire house (in-wall during construction), do they actually use 1694A throughout? Just curious if people use it mainly for short runs or for entire house projects.


Michael


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## CJO

It isn't that much more than most other cable. For me, it is just easier to use all the same cable rather than having to buy a couple kinds of different ones; especially since most cable isn't available unless you buy a spool.


CJ


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## tubeguy44

Quote:

_Originally posted by CJO_
*Running bundled cable, IMO, is much harder than doing individual runs. The cable is much less flexible and the bend radii depends on the thickness of the whole bundle, not of individual wires.


CJ*
the installers that pull wire for a living actually prefer the whole-house cable that contains two RG6 quad cables and two cat5e cables in one overall jacket.... they pull one run of this to every room in the house home-runned to a central location (usually in the basement)....


it is much faster than separate runs.... which results in a lower labor cost....


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## bmoore0

Chu Gai...


I am going to be running CAT5e (or 6) through out as well, interestingly enough I've got the same question about CATx cables - even among CAT5e or CAT6 there's a wide range of them to choose from.


The future proofing is the hard part - I can see GigE in the near future, but I don't know that SDI is ever a consumer application. I could see the COAX used for Satellite, OTA HDTV runs, Cable, plain vanilla RF channel 3 stuff... And maybe even using the coax for network traffic some day.


I thought about the single cable run, but not only is it pricey, if one of the cables in a run is bad, I have to re-run the whole thing (or just run a new one). In any case, I still would have to figure out which bundled cable I want then...


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## CJO

Quote:

_Originally posted by tubeguy44_
*the installers that pull wire for a living actually prefer the whole-house cable that contains two RG6 quad cables and two cat5e cables in one overall jacket.... they pull one run of this to every room in the house home-runned to a central location (usually in the basement)....


it is much faster than separate runs.... which results in a lower labor cost....*
It's the exact opposite in this area and with most of the large install guys I've talked to. Most of them do $100k+ systems and don't have the flexibility with the single cable system. Two RG6 and two CAT5 cables aren't nearly enough to most rooms and where they are enough, they wouldn't all be going to the same place anyway. To each his own I guess.


CJ


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## tubeguy44

Quote:

_Originally posted by CJO_
*It's the exact opposite in this area and with most of the large install guys I've talked to. Most of them do $100k+ systems and don't have the flexibility with the single cable system. Two RG6 and two CAT5 cables aren't nearly enough to most rooms and where they are enough, they wouldn't all be going to the same place anyway. To each his own I guess.


CJ*
i should have mentioned that this is generally for the whole house..... during new home construction..... with people that want to have tv, phone, and computer connections in every room....


doing a dedicated home theatre or complex audio distribution system, i agree with your assertion...


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## bunchman132

I prefer to run phone, cable, and network as seperate cables to bedrooms etc. I reserve Structured runs for special areas and any main TV or media room location.


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## Chu Gai

bmoore0

Well you certainly need to give this matter a bit of thought and if I may, perchance you're agonizing too much over minutae. While there are different flavors in the Category wirings, as there are in 75 ohm coax, you need to better define your requirements which should allow you to make a choice much easier. For example, do you really *need* Cat 6 for your home? After all, computers spend far greater time waiting for us than we do for them. Also, most people don't live in the same house forever so planning too long term may not be the most prudent or cost effective thing to do. Please avail yourself of the toll free numbers and speak to the companies directly.


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## Larry Fine

I'm not a big fan of all-in-one-cables because I generally don't want all of the connections in one place in a room. For example, in a bedroom, I like the phone near the bed, but the coax across the room. Not every room needs everything.


I have a customer (electrical) who had some co-workers of his low-voltage-wire his house (older house - gutted ane rewired as a new house). They used "structure cabling" all around, and can barely fit the cables into the panel. What a mess!


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## Bill Lummus

I agree with Tubeguy on this. Belden's own technical papers define their foil/braid/foil shield technology as the best EMI shielding they have. In their tests it was about 12x more effective than braid alone.


I also don't believe you can extrapolate their results to other companies.


When I get time I'll sniff around for more data.


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## bmoore0

foil/braid/foil is what shielding? QS? I thought that would be braid/foil/braid/foil?


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## Bill Lummus

The foil/braid/foil is the most shielding that they tested. They sell quad shielded cable and it's hard for me to imagine that adding another braid will degrade the shielding effectiveness. I could be wrong, though.


The also mention that the foil/braid/foil cable is the most expensive of the cables they tested.


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## CJO

The foil/braid/foil is triple shielding. They promote the quad shield as being more robust than the other types of shielding, they do not say that it does a better job at shielding EMI. Take a look at the belden website for more information.


CJ


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## KurtBJC

Quote:

_Originally posted by Bill Lummus_
*I agree with Tubeguy on this. Belden's own technical papers define their foil/braid/foil shield technology as the best EMI shielding they have. In their tests it was about 12x more effective than braid alone.
*
If you're referring to the Belden article titled "Cable Shield Performance and Selection Guide," it's true that the foil/braid/foil shielding did outperform the others on all test measures. However, it should be noted that when Belden prepared that paper (1983-1984) it didn't test the 95% copper braid/Duofoil combination. I'm not sure of this, but I think that Belden simply hadn't introduced the 1694A/1505A/1855A family of cables yet at that time, which would account for the omission. Steve Lampen, the Belden engineer who prepared the table in the article on our site, shows the Tri-shield cable as underperforming--albeit only slightly--the 95% copper braid/foil combination.


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## CJO

That makes sense- thanks for the update.


CJ


PS- by "our site," I assume you mean bluejeanscable.com?


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## KurtBJC

Quote:

_Originally posted by CJO_
*PS- by "our site," I assume you mean bluejeanscable.com?*
Yep, that's us...


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## Chu Gai

I'd say that the effectiveness of shielding is highly dependent upon the nature of the individual components that make up the matrix and of course, is manufacturer dependent. For example, consider page 2 on this link from westpenn... http://www.westpenn-cdt.com/pdfs/CX88.pdf 

In a home environment, where interference issues are no where near as severe as outside runs, other factors such as long term stability of the product (drop cables) take on a proportionally greater importance.


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## Bill Lummus

I can tell you that in my house the quality of shielding between the service entrance and my TV (about 50 feet) is the difference between being able to recieve and not be able to recieve several digital cable channels, among other issues.


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## tubeguy44

bill,


what cable do you use for your 50 ft run?


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## J. L.

Bill,


Unless the cable tv coax in your house runs adjacent to sources of electromagnetic interference in the 50 feet from your service entrance to your TV (past heavy machinery or motors, etc), I would doubt that the "high quality shielding" has anything to do with your ability to receive several of the digital channels or not.


Now, I have no doubt at all that a cheap brand of coax, with higher losses at higher frequencies, or lessor quality crimps, or a center conductor that is not truly "centered" along its length leading to impedance "bumps" would degrade the signal to the point of not being able to receive several of the digital channels, even with a 50 foot run. But the major factor involved is excessive attenuation of the desired signal, not poor shielding.


Those factors that affect signal attenuation (loss in dB per 100 feet at a given frequency) do not directly have anything to do with single shield, double shield, quad shield, etc type of cable, but instead more with the type of dielectric between the center conductor and the shield and the diameter of the cable and the distance between the inner conductor and shield conductor.


As many have said, a low loss cable with a high quality shield is desired for most installations. Your specific brand of "high quality shielding" coax is very likely to be lower loss as well. Typically, "fatter" cables have less loss than "mini" cables per foot. The better cables just happen to also have better shielding...


Joe L.


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## bmoore0

So I'm not sure I'm any clearer on the QS v. DS...


It seems like internally a good copper shield is probably sufficient (Belden 1694) - outside, from the HDTV antenna to the receiver (because it's outside) would QS be a better choice - i.e. when the cable run is mostly outside? Or would 1694 do just as well?


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## Larry Fine

Inside or outside, anything beyond one braid shield and one foil shield only makes it stiffer and possibly sturdier. Even 70% braid is more effective than most people realize.


A screen is as effective as a solid panel at blocking RF. After all, you can see the food cooking in your microwave oven, can't you?


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## Bill Lummus

Quote:

_Originally posted by J. L._
*Bill,


Unless the cable tv coax in your house runs adjacent to sources of electromagnetic interference in the 50 feet from your service entrance to your TV (past heavy machinery or motors, etc), I would doubt that the "high quality shielding" has anything to do with your ability to receive several of the digital channels or not.


Now, I have no doubt at all that a cheap brand of coax, with higher losses at higher frequencies, or lessor quality crimps, or a center conductor that is not truly "centered" along its length leading to impedance "bumps" would degrade the signal to the point of not being able to receive several of the digital channels, even with a 50 foot run. But the major factor involved is excessive attenuation of the desired signal, not poor shielding.


Those factors that affect signal attenuation (loss in dB per 100 feet at a given frequency) do not directly have anything to do with single shield, double shield, quad shield, etc type of cable, but instead more with the type of dielectric between the center conductor and the shield and the diameter of the cable and the distance between the inner conductor and shield conductor.


As many have said, a low loss cable with a high quality shield is desired for most installations. Your specific brand of "high quality shielding" coax is very likely to be lower loss as well. Typically, "fatter" cables have less loss than "mini" cables per foot. The better cables just happen to also have better shielding...


Joe L.*
I won't bore you with too many details, but it's pretty clear that shielding was a major issue in my signal problems.


I live near several TV and radio broadcast towers. The channels I have had trouble with- analog and digital- are carried on the same frequencies as the nearby broadcast towers. Upgrading the cable between the service entrance and my TV helped but didn't really "fix" the problem. It was very easy to disconnect the incoming cable and measure the signals being received on the lousy contractor grade cables initially installed in my house. They were a very effective antenna. I'm sure my neighbors appreciated it when I euthanized the stuff. My SNR improved by several dBs even on the TV that was not fed by that wire after it was removed.


Additionally I recently installed a ground loop isolator and began again to have trouble with two HD digital channels. Yep- these are carried on a frequency shared with a nearby broadcast tower. The retailor of the isolator told me it has only 60db of sheilding. When I wrapped it in aluminum foil grounded to one end- problem solved with a 2-3 db improvement in SNR. And this isolator is two inches long!


I'm sure there are other problems with my cheap wiring but shielding sure seems to be the main player. The problems didn't occur at the really HF channels and the problems persisted with the cheap wiring connected to the splitter- not necessarily feeding the TV directly.


I can give more details but I think you can draw your own conclusions. There is no downside I'm aware of to using a higher-quality well-shielded cable and in my case it would have prevented hours of crawling around in the attic and crawl space and several frustration headaches trying to troubleshoot a somewhat difficult and confusing problem. The difference in cost is inconsequential.


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## J. L.

Bill,


You clearly understand the need for 100% shielding when living in such close proximity to high powered radio and TV signals. Your situation is different than most folks. You need shielding AND a good SNR.


As an Extra class Amateur Radio operator I am very familiar with both RFI and front-end overload of consumer electronic equipment. When I lived in my previous house, I would wipe out certain cable TV channels if I operated my 2 meter transceiver nearby (they too shared the same frequencies)


I too installed quad shield coax to help with the situation. As you said, the cost is not that much more. Cable TV uses most of the RF spectrum from 3 MHz upward to 900 MHz sharing frequencies with lots of over-the-air radio and TV signals. I've spent plenty of time hunting and finding leaks in cable TV lines that caused interference to other radios nearby. Good shielding is important for both to work as intended.


Please accept my apology. Next time, I'll start with "Unless the cable TV coax in your house runs adjacent to sources of electromagnetic interference between your service entrance and your TV (past heavy machinery, motors or *nearby transmitters*, etc)"


Joe L.


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## Larry Fine

Interesting additional info: The local cable co. had so much ghosting on local channel 6, they had to remodulate it onto channel 9 on cable.


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