Topband: Problem with compression F connectors on Quad RG-6

[Michael Tope]

On 5/7/2013 7:33 AM, Paul Christensen wrote:
>> The standard drop cable is a bonded foil with single braid, it has 
>> been that way since the late 1970's. The current best grade is 
>> "Brightwire" by CommScope. Any good cable will far exceed FCC specs 
>> without a quad shield.
>
> It remained that way with Comcast & AT&T Broadband at least until 2002 
> when I left AT&T corporate engineering, shortly after the merger.  I 
> doubt much has changed since then.
>
> Concerns are a bit different in the broadband world where downstream 
> leakage must be minimized between 50 MHz - 1 GHz.  The upstream path 
> is in HF region, but no sane cable operator uses spectrum below about 
> 10 MHz.  The only services anywhere near that area of spectrum are 
> used for data transponders and IPPV from the set-top box where 
> modulation is almost always QPSK.  Telephony and DOCSIS cable modem 
> service is all relegated to an area above 20 MHz.  In the Jacksonville 
> Comcast system, it's now all above 30 MHz which was made possible 
> through the use of tighter diplexer specs in the system amps and 
> fiber-optic nodes.  if you could see a spectrum analyzer display of 
> the return path back at the headend, you would be amazed that the 
> return path works at all. Any point of ingress results high levels of 
> interference, most notably SWBC.
>
> I recall writing up a paper in the mid-'90s that predicted a need for 
> better return path certification and an upward move of the lowest 
> usable frequency to well above 20 MHz.  I pointed to the 11-year 
> sunspot cycle as an important driver.  The non-ham engineers in our 
> group didn't get it.  But the CTO of MediaOne was a ham, and he did 
> get it.  The public did not know it, but there was a real fear between 
> 1995 and 2000 that return path broadband technology would never work.  
> When you consider all the points of potential failure, especially on a 
> power-passing system, it truly is a miracle that it works at all.  
> Consider this: The typical fiber-optic node services between 200-500 
> home passings.  From the comfort of your living room, and with an RF 
> signal generator, one can wipe out an entire service area when the 
> return path frequencies of the system are known.  This isn't 
> theoretical, I demonstrated the impact to a sober group of engineers 
> with an Eico generator.  That potential still exists today.
>
> Concerning SANS connectors and wiring, I would take the lead from the 
> cable operators.  They cannot afford to have unreliable cables 
> anywhere between the customer equipment and the headend or hub 
> facilities.  When you've got thousands of miles of cable plant and 
> interfacing hardware, that becomes the most important piece in the 
> network.  If a router, modulator or fiber amp fails in the system, the 
> fix is easy with money.  But if you deploy bad cable and hardware into 
> a system, you'll feel the pain a long time as it affects long-term 
> service call volume, unhappy customers, and angry government leaders 
> who generally hate the cable operators.
>
> Paul, W9AC
>

About six months ago, our garbage truck hit the sagging telephone/CATV 
drops that serve my house and my neighbor's. It took several days to get 
a response from Time Warner despite the fact that the cable was hanging 
at neck level at times (we pulled it up the best we could only to see it 
get knocked down again by the various delivery trucks that come through 
the neighborhood). In any case, when Time Warner finally responded, I 
saved the discarded drop cable and took it up to my station in the 
desert north of here. I didn't pay close attention to it at the time, 
but this discussion got me to wondering what sort of shielding was used 
in that drop cable, so I retrieved some last time I was up there. This 
evening I took a close look at it.

The drop cable is Times Fiber Communications (TFC/Amphenol) T10 
"Teledrop". It look like an RG6 (I didn't measure the diameter) paired 
with a messenger on one side and a telephone twisted pair on the other. 
The coax is tri-shield (bonded inner tape layer, braid, and outer tape 
layer). There also appears to be some sort of sticky flooding compound 
which may be TFC's "Lifetime" non-drip/non-leak flooding compound (see 
page 85 of the following):

http://www.timesfiber.com/TFC_Cable_Book_III.pdf

The other interesting information in the TFC Cable Book III is Technical 
Note 1025 "Drop-Cable Transfer Impedance" starting on page 70. What this 
note says is that you can't ignore cable aging due to flexure and 
corrosion when looking at shielding effectiveness. Comparing the 
shielding effectiveness at beginning of life (BOL) can yield vastly 
different conclusion compared with shielding effectiveness done on cable 
that has experienced significant environmental exposure. Quad shield 
seems to have been developed to address the problems that come from foil 
seam separation that occurs as the result of drop cable flexing. It's 
actually a pretty complicated trade space which may explain some of the 
lack of consensus in this discussion.

73, Mike W4EF................