Pointer: Using wireless modem over coaxial cable link

That's a mighty big and expensive coax cable.

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.

A few notes:

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.

1. Laying coax in residential areas is always a problem as anything that crosses the property line involves considerable bureaucracy. However, a tolerable rule might be "if they can't see it, they can't complain about it".

I live on a semi-rural owner maintained marginal road. Many years ago, when I installed my first bootleg CATV system, I did some horizontal drilling under the road for the cable. No big deal with the right equipment. |

course, I didn't do it with such expensive equipments. I just used a big steel pipe with some teeth ground into the end, a water hose down the center, a chain drive, and a big motor (1 hp?) and gearbox. It lasted long enough to drill 3 holes across the road before the pipe bent, breaking the chain. After drilling, we pounded in a few lengths of schedule 40 pipe.

1. There is a better way. FTTS (Fiber Through The Sewer): |
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2. If you don't mind going through the air, there's the G-Line (Goubou Line): |
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   low loss but must run in a straight line.

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

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.

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.

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..

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.

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

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

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.

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

Old guy

The surface transmission occurs between the conductor and the dielectric insulation. A bird sitting on the wire would not act as much of a reflector. The unavoidable cable droop isn't much of a problem as long as it's gradual. There have been tests using seriously dropped PG&E power lines which found that it works well enough with the droop. However, the relatively sharp bend at the insulators on the pole are a problem. There will be some radiation (and therefore some loss) at this point. The amount of radiation is determined by the bend angle.

Dunno. A few thousand volts. Porcelain capacitors should have the voltage rating and not turn into inductors at 2.4GHz.

However, I can see construction problems. Perhaps using the same trick as the "through the glass" car antennas might be a better idea. We're only concerned about 2.4GHz, so a frequency selective transformer or antenna would suffice. Just put a loop antenna, biquad, or patch antenna at each end. Move the access point close to the antenna. Instant isolation.

Sorry. That's an act of God and is not covered in the warranty.

Two helical resonantors in a can acting something like an xformer. Float one or both connectors.

The insurance company doesn't require disclosure. However, if it can demonstrate a non-code compliant installation, they can easily deny the claim. It doesn't matter if it was done correctly. It only matters that the proper building permits were issued and signed off.

That's what I expected.

I never had a situation where G-Line was going to be a solution, so I didn't look into it very closely. I knew it wanted dead-straight runs and that if you wanted to turn a corner you might want to have a pair of launchers connected by some other form of transmission line to do so.

I no longer have all of my catalogs, but several vendors used to sell these - I remember Omni-Spectra being one. Basically, they looked like a barrel connector (either same sex, or M/F). They were available as Inside, Outside or Inside/Outside blocks, and the ones I used were 'OK' (meaning loss and VSWRs not much worse than a connector pair) from mid VHF (call it 50 MHz) up to the cable/connector maximum. They were rated at something over 250 volts (DC or peak). A _very_limited_ google search turned up few hits, and the top one was only talking about 50VDC. Of course, you could fabricate something on stripline, but as you point out

That would probably work.

Me and my lawyers are Atheists (was going to say 'Agnostics' but that probably wouldn't float).

That's also a good idea if the Q isn't to high.

Don't I know that. I've still got copies of a Survey Report after a heating contractor installed heat pumps on a trailer but neglected to install the duct and insulation where the air outlet entered the distribution ducts. The result was charring and an eventual fire from the very hot air from the heating impinging on the wooden frame of the trailer. The government inspector had signed off the work - and the contractor's insurance carrier wiggled free (though I doubt the contractor did any more work for NASA). They also pointing fingers every which way at other things being the cause of the fire.

Old guy