Coaxial Cable or Circular Waveguide

Posts: 492

As I'm sure most of us have, I have a respectable collection of assorted cables that have piled up in a drawer over the years. I was looking for a short piece to connect two phase splitters in order to connect two TV's when I noticed that the newer cables were distinctly different from the old.

The old cables, RG75 if I remember correctly, were thinner than the new cables. They were also shielded with cheap copper braiding and had a sloppy connector. A plain old coaxial cable for sure. I had a roll of the newer cable for comparison. Thick, nonflexible and expensive connectors. The shielding proved to be something special. A solid stainless metal was wrapped around the inner insulator. It was fixed to the insulator with some sort of adhesive. The distance from the center conductor to the shielding was perfectly uniform throughout the length of cable.

I did microwave work years ago when I was a younger man. It seemed likely that what I had been examining was in fact a circular waveguide. I don't remember when Comcast had switched to this type of device. I assume the cable came in when the data rates went up. Impressive to say the least.

I think I'll be taking much better care of these cables from now on. Don't step on it, no crimps or sharp bends. I don't know enough about what goes through these cables. What are the standing wave ratios? How does a standing wave affect data rate, voltage, and rise times? Then again maybe it doesn't matter at all, or is a poor cable the root of some of the Broadband Router problems that some experience?

Posts: 78 · Posted: Sat Feb 05, 2005 8:38 pm Post subject: Ah, the good old days

While I was still active in the amateur radio field we used Belden 9913 cable. That stuff was rated for use from 144MHz to 1.2GHz or so without any serious attenuation.

Of course the gold standard was hardline. Hardline used an aluminum outer shell surrounded by polyeth or something similar. Inside was the center copper conductor supported by nylon supports every so many cm. That stuff was good for pretty much anything you throw at it with low attenuation of signal.

Many cable companies used it for their backbone before switching to fiber.

Posts: 492

Ah! Amateur radio. I was once WB1AUJ. General class license. I can't remember the equipment manufacturer, it was common and a twin setup. That was over 30 years ago. Lost interest quickly. Got tired of QSL?