Re: Pointer: Using wireless modem over coaxial cable link

On Mon, 17 Jul 2006, in the Usenet newsgroup alt.internet.wireless, in article
<4k1ob2ldeq8nljmhrfkruco5rfbqbpns4j@xxxxxxx>, Jeff Liebermann wrote:

That's a mighty big and expensive coax cable.

No kidding. I had a 5000 foot length of a 1/2 inch 75 Ohm buried in a
simple trench (dug with the angled blade of a a road grader - about 9
inches below grade). I'm pretty sure it was a Times Aluminum foam
type (complete with steel tape armor and flooding compound) - and the
cable and trenching cost nearly US22K in the late 60's. I'd hate to
think what it is now.

75 ohm coax cable has less loss per foot than 50 ohms. Also, once the
loss gets above something like 20dB, any reflections from the far end
will never be seen by the near end. Therefore, VSWR is not really
that important.

My take was that the VSWR of the cable was still substantially better
than the "normal" VSWR of most antennas. If we really were concerned
about VSWR, a quarter wavelength of 61 Ohm line brings that into reason,
though a stub match would likely be easier to fabricate..

1. Comcast was looking into doing Wi-Fi over home CATV cable for a
while. It worked quite nicely but ran into a stupid problem. The
quality of the average home CATV wiring is so poor that chances were
high that sloppy connectors and crappy coax would turn it into a
maintenance nightmare.

I can believe that - the "quality" installation I've seen used something
similar to RG-6 (but with a foil and braid rather than silver inner, copper
outer braid) from the street to the wall jacks, with type F connectors. I
suppose that coax is better than the RG-59 look-alike used from the wall
jack on, it's far from a really decent cable. I don't like single braid
coax above 800 MHz, even though spec-sheets often had imaginative numbers
up to several Gigs. I know that RG-58 was a pretty good antenna at 5 GHz
(it sure didn't act as a coax), and expect RG-59 to be similar. The
connectors? Powdered plastic doggy-doo.

3. There is a better way. FTTS (Fiber Through The Sewer):

That would be my preference. Dunno what the costs are like.

4. If you don't mind going through the air, there's the G-Line

Very low loss but must run in a straight line.

How does that handle birds parking on the line - and catenary suspension?

Two small capacitors. One to the center conductor and one to the
shield should be sufficient isolation. 50 ohm termination optional.

Outside/Inside DC Block - but what voltage rating? Actually the concern
I have is lightning. By the time we had our "very nearby" strike (a few
hundred feet from one end of buried cable above), that run had been
decommissioned. However, buried phone lines did have a problem that I
determined was likely due to substantial differential ground levels
at the ends of the cables. While there was lightning protection, the
active stuff attached to the lines failed (as best as I could determine)
from exceeding common move input levels on the chips.

I don't know which would be a better idea - the DC blocks, or powering the
access point at the "ungrounded end" via an isolation transformer, and
locking the box in an insulated cage, with a short fiber link between the
access point and the local computers.

Because there is no specific electrical code chapter and verse for
such an installation, even if you do it the right way, it's possible
for the insurance company to claim that it started a fire.

or that any damage isn't covered because you didn't inform them of this
hidden cable.

Old guy
.

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