What is the best way(hookup) to "test" cables like these to see if they are resonant on a particular freq? With or without the coupling loops attached etc. for duplexers say
Mike ----- Original Message ----- From: Nate Duehr To: [email protected] Sent: Thursday, July 24, 2008 3:56 PM Subject: Re: [Repeater-Builder] Duplexer cables Alexandre Souza wrote: >> For RG214 which has a velocity factor of 0.66 at 147 the cables would be >> about 13.25 inches. Now the type of connectors can influence this in that >> the connector type might lengthen the cable. N-connectors protude beyond >> the cable where PL259s do not. > > Now there is an intersting question from a "kind of" newbie: Connectors > crimped/solded, where does you measure the total lenght of the set (cable + > connectors)? On the base? Middle? where? The "correct" answer is whatever their electrical length is according to the manufacturer. The real-world answer is... trial-and-error mixed with knowing that a centimeter or so usually doesn't make much difference when you're talking VHF and probably not at UHF. Go higher in frequency, and you have to be more accurate. The only way to see the real-world results is by making a few cables and comparing them on the bench. Once you find connectors you like that are high-quality, and you've figured out how they behave... "If I use this connector my test gear always says the cable is about X too long"... then try to keep that style connector on-hand for such detail-oriented projects. Some connectors you can "get away with" inserting the coax but not crimping them down to get a rough feel for how the cable is acting. It's not perfect, but if you start long, you can often trim down to where you need to be before you crimp the (admittedly expensive) connector down onto the cable. Making custom length cables is a giant PITA. Take your time, experiment, get them just right by looking at them with real test gear, and then forget about them for years... (GRIN). Nate WY0X
