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April 10th 07, 03:34 AM
posted to rec.radio.amateur.antenna
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Coaxial Cable considerations for HF
Bryan wrote:
John wrote: Having re-entered ham radio after a 30 year hiatus, I would like to ask about RG/8U versus other cable types for use in a simple dipole or G5RV installation with 100W max. transmitter output. In the "good old days" Low loss "8U" was sort of the standard. There are some newer cable designations now. Is there a better "standard" cable for the above use than RG/8U (specifically Belden 9913 low loss)? John AB8O Hi John, Some useful information and history is he http://en.wikipedia.org/wiki/Coaxial_cable. For a given type, you'll find quality all over the map, from decent to downright crummy. That said, I recommend a looking at a prospective manufacturer's datasheet before buying. If there are no specifications available, keep looking! When it comes to loss/length (for a given cable type), foamed polyethylene dielectric will be better. Percentage of shielding is probably the next determining factor. An aluminum foil shield of course will be 100%, but won't take much flexing before fracturing. Save it for long runs that are secured in place, and use braided copper or braided copper + foil for other uses. You'll find most all manufacturers make cables with as much as 97% braided copper shielding. The last item of concern will be the outer jacket. PVC is the most common. Some are "non contaminating" or "UV resistant" types that degrade much slower in sunlight. Use a UV-resistant type for outdoor applications. Belden 9913 has a "Semi-Solid Polyethylene" dielectric and can't handle tight-radius bend. It also has a solid center conductor, which doesn't like repeated flexing. The shield is "100% coverage Duobond tape" (foil), which also doesn't like repeated flexing. RG-58 types are rated to 250W (under matched conditions) safely. If you plan on running higher power and/or longer runs and/or high standing waves on the feedline, you should consider something larger. Many hams have used RG-8X (also called "mini RG-8") with good success. If you're cost-conscious, this might be a good choice. Ralph mentioned LMR400 as having a copper coated aluminum center conductor. It's made by Times Microwave Systems (http://www.timesmicrowave.com/) and is a solid conductor. Their Ultraflex version (LMR400UF) has a stranded bare copper inner conductor. He also mentioned Davis RF (http://www.davisrf.com/) having Buryflex available. As far as I can see, it's LMR400UF with a different brand name on it. By the way, I've dealt with them once... very good folks. Vy 73, Bryan WA7PRC Thanks, Bryan, for the knowledgeable tips. |
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