Re: Waveguide (was "size a major consideration...") [Telecom]

What puzzles me is how microwave could be retired in favor of > fiber, given the immense investment required to lay it: the > cost of labor alone would dwarf all other considerations. How > is fiber so much "better" than microwave? > Did we just run out of radio channels?

Frequency congestion was certainly a factor, but I think path congestion was a bigger factor. In order to avoid interference among microwave paths, FCC rules require frequency coordination for any new microwave path, or any new frequency use over an existing path. Under this process, every license application must include a technical study showing that the proposed antenna would not cause interference to, or receive interference from, any existing terrestrial microwave antenna using the same frequencies. As installed capacity grew, it became ever more difficult to coordinate further capacity.

For common carriers using the 4-GHz band (3.7-4.2 GHz), this problem became even more acute with the rise of C-band satellite antennas for television signal distribution. Licensed C-band TVROs were usually licensed for the entire 4-GHz band, effectively blocking construction of any microwave link that would interfere with it.

Here is a link to my previous post about this subject:

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Bill continued:

Capital Cost - I'm sure fiber is expensive to lay, but I > suspect the rights of way are the big expense, and Microwave > doesn't have that problem.

Right of way can indeed be expensive, but it depends on where you put it. For construction in existing recorded easements and along state and federal highways, ROW costs are usually limited to actual construction costs plus pole rental if applicable.

Utility companies (including cable TV companies even though they're not utilities under federal law) have the right to use any existing "compatible" recorded easement, subject to any restrictions set forth in the easement document. The definition of "compatible" has been the subject of some litigation, but the law is on the side of the utility.

State governments usually don't impose rental charges for utility facilities within state-owned ROW along state and federal highways. (The same cannot be said for county and municipal ROWs, but that's a subject for another day.)

The biggest drawback to construction on highways is the instability of the property. Highway departments frequently do disruptive things like widen traffic lanes, clean ditches, install culverts, install signs, and plant landscaping. Adjacent landowners are forever mucking around planting trees, building driveways, installing signs, and anything else you can imagine.

For long intercity runs, the most stable ROWs are along railroads. Unfortunately (for the utilities), railroad companies are keenly aware of the value of their ROWs, and they charge accordingly. I've encountered charges as high as $1.00 per foot per year for aerial crossings. That might not sound like much, but it sure adds up fast! (Factoid: many cable TV systems are designed as two separate networks interconnected with ONE railroad crossing.)

As for common carriers like AT&T Long Lines, if they've already reached capacity along existing microwave routes, building new microwave capacity can be extremely expensive if not impossible. In urban areas, it may not be possible to frequency-coordinate any new usable paths due to potential interference to/from existing links and licensed TVROs.

And even if they build new capacity, it may not be enough for future expansion. By contrast, as others have pointed out, fiber has orders-of-magnitude greater capacity than microwave,

Bottom line: installing fiber may be the only option, even at railroad companies' rental rates.

Neal McLain

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Neal McLain
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