On Wed,3/29/2017 11:47 AM, Ron D'Eau Claire wrote:
An SWR approaching 10:1 means high RF voltages on a coaxial line at the voltage loops
Remember that the SWR on a transmission line, and thus the loss in the line, is determined ENTIRELY by the match between the antenna and the line, NOT between the line and the transmitter.
The SWR measured at the transmitter is a measure of the difference between the impedance the transmitter WANTS to drive and the impedance of the load connected to it. If that INDICATED SWR is high, a solid state transmitter will "throttle itself back" to protect itself, but that's not LOSS. The function of an antenna tuner is to make the transmitter happy by giving it a load that it's designed for, so that it can put out its full power.
For example, a long wire antenna of random length might be nowhere near 50 ohms resistive, so must be transformed to 50 ohms resistive so that the transmitter can put power into it. Likewise, an antenna perfectly matched to 75 ohm coax or 150 ohm twin lead has no excess loss in the line but needs a matching network to make the transmitter happy. My high dipoles (at 100 - 140 ft) are fed with 75 ohm coax to minimize the loss in the line.
73, Jim 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 Message delivered to [email protected]
