Tech Net Notes February 27, 2009

The theme for the February 27, 2009 edition of the Tulsa Tech Net was coax. As most of us have found out by now, there are a lot of varieties of coax out there. Big coax, little coax, medium coax, stiff coax, flexible coax, and stranded vs. solid center conductor. (not to mention the electrical characteristics variations) Some coax jackets are more durable than others. What we would like to know is, "What kind of coax do you use?" What problems have you encountered? What works best? What is your coaxial philosophy?

aa5ss, Glenn, said that he didn't have very good luck on one of his two meter antenna installations using coax. He said it was too lossy. He said that he was able to make some twin-lead work better for the installation of the antenna in his tree.

ke5lep, Stan, had a question, "What works well for jumpers? Big coax is cumbersome; small coax is lossy. Plus, it's understood that the more connections, the more the loss. What is the recommended size and type of coax between switches, meters, equipment, and antennas?"

ki6und, James, mentioned that using equivalent products would be best, in that the entire transmission line will take on the characteristics of the least common denominator, or "weakest link".

kd5njr, Scott, said that a good rule of thumb is that each connector will cost about .2db a piece. He said he agreed with the "weakest link" comment.

kd5vsf, Terry added, "Ground your system with heavy wire to a good ground. Check your specs for the frequency you'll be using most. One of the best instruments for checking things is the MFJ antenna analyzer. Also get good reference material, such as those publications from ARRL."

kd5njr, Scott, came back in and said that the Belden 9913 (or compatible) cable is a good type for jumpers.

ki6und, James, followed with another question, "Is there a way to negate the loss from a connector?"

kb5vdb, Ron, had to say, "Get the best connector you can get. A lot of the loss is relative to the frequency you are using. In some instances you can reduce loss by matching the connector with the frequency you'll be on."

kd5njr, Scott said "...just keep an eye on your connectors. Keep them clean. Use a light electronics cleaner. Keep them clean and free of debris. The worst thing you can do is splice your coax. LM400 is tough to beat."

ke5y00, Mike, says, "As far as coax goes, I just use what I have. As long as you keep it short, you can get away with a lot. I try to keep my length down."

kb5vdb, Ron, added, "RG8 is a military designation. There are several companies that manufacture it...just because it says "RG8" does not necessarily mean that it meets stringent operational specifications. There are a few quality companies out there that manufacture good products, such as Belden and LMR."

kd5vsf, Terry, said, "Keep an eye on that RG59, that can be a bad mismatch on an HT."

kd5njr, Scott said that compared to RG8, RG6 is better for antennas, loss-wise, even though it is 75-ohm and a mismatch. If you have a lot of RG59, look up "1/4 wave transformer" on the internet, for ways to use it.

w5taz, Dave said, "When they talk about balums, there is a big impedence, but when you're talking about the difference between 50 and 75 ohms, there's not that much difference."