[mythtv-users] Long coax (was Re: Questions about Hauppauge...)

Brian Wood beww at beww.org
Thu Jul 3 19:59:15 UTC 2008


On Thursday 03 July 2008 13:32:10 Alen Edwards wrote:
> Peter VanDerWal wrote:
> >> Thanks.  I'll probably give it a try.  For right now at least the STB,
> >> HD-PVR, and TV are all in the same general vicinity.  I can probably
> >> get away with 3 foot runs (maybe even less,
> >
> > -snip-
> >  I may eventually
> >
> >> move the HD-PVR closer to the back-end.  This would mean probably a
> >> 25' run, but it sounds like even at that distance you are not having
> >> any quality issues.
> >
> > I used the RapidRun coax system.  It's a bundled, 5 coax, cable with a
> > single multipin connector on each end.  Then you just buy appropriate
> > wall plates (HDMI, Component + audio, Composite + S-Video, etc.)
> > It's good quality stuff, easy to pull, and looks professional when you're
> > finished. Plus it's reasonably priced.
> >
> > http://www.amazon.com/25ft-RapidRun-Video-Runner-Cable/dp/B000YTPA52/ref=
> >sr_1_17?ie=UTF8&s=audio-video&qid=1215107352&sr=1-17
> > http://www.amazon.com/Cables-Go-RapidRun-Component-Wallplate-White/dp/B00
> >0CPQ7YQ/ref=sr_1_2?ie=UTF8&s=electronics&qid=1215107462&sr=1-2
>
> That is good looking cable and indeed reasonably priced.
>
> Just to throw another option into the mix, I use this stuff:
> https://www.tselectronic.com/belden/9116.html
> One thing to consider in long runs is the loss in the cable.  An easy
> way to evaluate that is that the fatter the cable, the lower the loss.
> A bundle of these will be much fatter, and thus much less loss than any
> multimedia cable.  On the other hand, what you listed is probably good
> enough and has some other stuff in the bundle that makes it attractive
> for applications where it fits.
>
> It is hard to beat coax though.  A 25 ft run of 3 coax cables would be
> about $6.  Of course, you have to buy 1000 feet to get that price.  I
> have a lot of cable left over but then again this is my second box.
>
> I have used it for antenna feeds, S-Video, Component, Composite, and
> audio (preamp out with distribution amp).

Different types of coax are designed for different uses. For example, the 
Belden 9116 referred to above has a copper clad steel center conductor. This 
is designed for CATV applications where mechanical strength is required, as 
with aerial drops. Steel is not a great conductor, but at RF frequencies, 
where the "skin effect" is a major factor, this is not a big issue, but I 
would not use such cable for baseband video, where low frequency response is 
required.

Obviously a steel center conductor has an impact on bend radius as well as 
strength.

Some cable uses solid plastic dielectric, others use a foam type. Solid 
plastic has greater strength, but at the cost of higher loss at RF 
frequencies.

Soft-drawn copper is a great conductor, but has low strength and can't 
tolerate a lot of flexing.

Times Wire and Cable once made (and maybe still do) a special "head end" cable 
with a 60% silver/40% soft copper center conductor and a double copper braid. 
This stuff weighed about 5 times what normal CATV cable weighed but had great 
electrical properties (it was also very costly).

Multiple shields are sometimes required for CATV in some environments. 
Aluminum shields are often used for CATV where low weight is a factor, as is 
low cost.

Physical properties like bend radius, strength, weight, water resistance, UV 
resistance and others, as well as electrical properties like forward loss, 
maximum rated frequency, return loss, characteristic impedance and others all 
have to be considered in choosing the proper cable for a given application.

Another very important factor, especially with RG-59/RG-6/RG-11 type cables 
that use crimp type connectors is that you must use the correct connector for 
the cable in use. There is no such thing as a "one size fits all" crimp 
connector, and a lot of problems happen because the wrong connector was used.

There is a reason that hundreds of different types of coax cable and 
associated connectors are made, you have to choose the best one for a 
particular application. Just using what your local Radio Shack has in stock 
has led to a lot of problems :-)

beww


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