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Thinking about setting up a repeater? COAX guidelines
COAX Guidelines (Extracted from industry voices):
These are considered industry best practices.
In duplex service you want to avoid any coax that has dissimilar metals rubbing against each other (Such as Belden 9913) or any LMR-(Any 3-digit or 4-digit number) cable since both use an aluminum foil shield rubbing against a copper braid.
In a coax cable any dissimilar metals in contact with each other are bad news. Aluminum oxide is formed when raw aluminum is in contact with oxygen, and the chemical reaction that converts the top few molecules of the exposed surface of aluminum into aluminum oxide is almost instantaneous.
Aluminum oxide makes a dandy diode. All those millions of contact points between the copper braid and the aluminum oxide layer on the aluminum foil become millions of little tiny diodes.
In the presence of RF power levels over 20 watts all of those little diodes cause RF noise.
The amount of noise energy on any one frequency (Such as on your repeater input frequency) is at low level, but when you have the noise source inside the same feed line that feeds a sensitive receiver it doesn't take much level to be audible.
“Any cable that has dissimilar metals pressed together, even inside a jacket, will sooner or later create wideband noise (Sometimes called duplex grunge) when hit with RF power greater the 20 watts.)”
With that said the preferred brand of coax in the two way radio industry is Andrews heliax. It is available in sizes ranging from ¼ inch, 3/8 inch, ½ inch, 5/8 inch, 7/8 inch, 1 and ¼ inch, and 1 5/8 inch.
You will also want to use all silver plated connectors and absolutely minimal adapters (If adapters are needed they also need to be silver plated) in your connections from the transmitter or receiver to the duplexer, from the duplexer to the feed line and from the feed line to the antenna.
NO nickel plated or chrome plated anything in the RF path anywhere!
Nickel and chromium are ferrous metals and as such both are an intermod creator anywhere around RF and are detectable at 10 meters, 6 meters and has proven to be a real problem at 2 meters, 220, 440, 900 and 1200 MHz.
Mark Abrams WA6DPB said it well when he said "One nickel or chrome plated anything can really ruin your whole day". Another rule is nothing but Teflon™ insulated silver plated connectors and minimal adapters on anything above 30 MHz.
These are considered industry best practices.
In duplex service you want to avoid any coax that has dissimilar metals rubbing against each other (Such as Belden 9913) or any LMR-(Any 3-digit or 4-digit number) cable since both use an aluminum foil shield rubbing against a copper braid.
In a coax cable any dissimilar metals in contact with each other are bad news. Aluminum oxide is formed when raw aluminum is in contact with oxygen, and the chemical reaction that converts the top few molecules of the exposed surface of aluminum into aluminum oxide is almost instantaneous.
Aluminum oxide makes a dandy diode. All those millions of contact points between the copper braid and the aluminum oxide layer on the aluminum foil become millions of little tiny diodes.
In the presence of RF power levels over 20 watts all of those little diodes cause RF noise.
The amount of noise energy on any one frequency (Such as on your repeater input frequency) is at low level, but when you have the noise source inside the same feed line that feeds a sensitive receiver it doesn't take much level to be audible.
“Any cable that has dissimilar metals pressed together, even inside a jacket, will sooner or later create wideband noise (Sometimes called duplex grunge) when hit with RF power greater the 20 watts.)”
With that said the preferred brand of coax in the two way radio industry is Andrews heliax. It is available in sizes ranging from ¼ inch, 3/8 inch, ½ inch, 5/8 inch, 7/8 inch, 1 and ¼ inch, and 1 5/8 inch.
You will also want to use all silver plated connectors and absolutely minimal adapters (If adapters are needed they also need to be silver plated) in your connections from the transmitter or receiver to the duplexer, from the duplexer to the feed line and from the feed line to the antenna.
NO nickel plated or chrome plated anything in the RF path anywhere!
Nickel and chromium are ferrous metals and as such both are an intermod creator anywhere around RF and are detectable at 10 meters, 6 meters and has proven to be a real problem at 2 meters, 220, 440, 900 and 1200 MHz.
Mark Abrams WA6DPB said it well when he said "One nickel or chrome plated anything can really ruin your whole day". Another rule is nothing but Teflon™ insulated silver plated connectors and minimal adapters on anything above 30 MHz.