In a message dated 09/02/05 20:33:27 GMT Standard Time, [EMAIL PROTECTED] writes:
As for the matter of running a 50 Ohm source into a high Z scope input, Tek has a slick solution. They use these 50-Ohm 2-Watt terminators that you apply right at the BNC connector at the scope input I picked up some of those with an ex military scope probe kit. Previously used a BNC T adapter with a 75 ohm termination on the spare port for CATV testing with a scope where a terminated line was required. A 50 ohm termination could be used in the same way if only one has the facility to dissipate the 10 or 100W as needed. What I did for this purpose for 2 way VHF radio testing in earlier times was to borrow an idea from the CATV industry where close into the line amplifier, the tap off unit from the coax feeder line (T unit) is constructed from a resistive divider to provide the necessary attenuation. These can contain as little as a single resistor or can be of the terminated type. For my purpose an attenuator was made up in a small in line filter box with a straight through connection which goes from the TX to the dummy load. Off this a resistor or a string of resistors is arranged from the center conductor to a socket for feeding into the test equipment. The test equipment socket was also terminated to achieve optimum attenuation. Once the voltage level has been reduced to reasonable levels cheaper low power coaxial attenuators can be used if needed. The resistors have to be carbon or other non inductive types and the divide ratio/resistor wattage can easily be work out by math. Made this up many years ago and still have the unit today. It is amazing what one can do with bits of junk when you have hardly two cents to rub together! The old UK made, KW Electronics PEP meter which can measure up to 300W worked in a similar fashion I found years later was using a resistive divider to bring down the voltage levels from the through RF to a level that can be used by the metering circuit. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
