On 9/11/2011 5:20 AM, Bill W4ZV wrote: > There is a loss graph on page 2 below but I believe ET3PMW's losses were > much higher. Of course this could have been due to poor quality wire > available in Ethiopia.
At HF, loss is essentially due to the resistance of the conductors, plus whatever loss there might be due to mismatch. For matched loads, the current is less with higher impedance lines, so the loss is less. Most zip cord uses relatively small conductors. BTW -- have you ever noticed that the Red/Black glorified zip cord sold at hamfests by CB radio dealers is often smaller than it is marked? BIG insulation, very small copper. Advertised #12, but try stripping it and taking a micrometer (or ohmmeter) to it. Let's compare it to RG58 can be pretty lossy too, depending on how much copper was used to build it. At 10 MHz, the published loss data for Belden RG58 cables varies from 1.1 to 1.5dB/100 ft. That loss is ALL due to copper, and at 10 MHz, skin effect dominates. The shield in these RG58 cables is a MUCH greater diameter than in the zip cord, so the loss in the shield is a lot less than for the zip cord, which can be #18 or smaller. Another suggestion to our friend in ZL. Here in North America, cable TV companies use millions of feet of 75 ohm 1/2-inch hard line. Installation companies have no use for short lengths of cable, so it goes in the trash, and short lengths to these guys is often several hundred feet. If we make friends with our local CATV company, we are often able to replace the word "trash" with the words "back of my pickup." Loss data for this cable is roughly the same as for 50 ohm hard line. About two years ago, I inherited a very large spool of this stuff from a SK. I am currently installing two monobanders for 20M and 15M on a new tower, and have cut lengths of 1/2-inch hard line to feed both of them. One of them is already operational and works great. If you google, you will find excellent information about practical and technical details for using this stuff in your ham station, including how to easily fit PL259 connectors, and how to cut the cable to a whole number of half wavelengths so that the impedance is not transformed by the cable. Some very useful websites I found are by W9XT and N1GUN. There's also a nice piece that ran in the VHF column of QST in 2000. Search the ARRL website to find it. I'm in the process of putting together something myself that shows loss data and an alternate method of installing PL259 connectors. I found another piece on the internet that correctly observes that this coax can make stubs that are a bit higher Q than most other available coax. Higher Q means greater attenuation, but also narrower bandwidth for that attenuation. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
