What an "antenna tuner" does for you depends upon where you install it.
There are two places where a low SWR is important: the load the finals in the rig "see" and the load the transmission line "sees". In most HAM installations the load the finals see is probably the most critical because if it is not within specs the transmitter may shut down or the final amplifier devices may self-destruct. Fortunately, Elecraft rigs have protection against self destruction by reducing the output power as needed but having the power reduce automatically is seldom desirable to the operator. Before about the 1960's, the output tuning networks in Ham transmitters were adjustable to provide a decently-low SWR to the finals with a wide variety of loads. Back then with vacuum tube amps it was common to "dip the plate current and adjust the loading for rated plate current at the dip". That adjusted the output network for a proper match to the finals, but required adjustment when QSYing. Then "no tune" rigs appeared which met the more stringent FCC requirements for suppression of spurious emissions but required a proper load: typically 50 ohms non-reactive. A lot of antennas did NOT provide a "proper load" to the rig, so the use of antenna tuners became popular. Many rigs built the antenna tuner into the rig itself to ensure the final amplifier transistors (or tubes) always saw an acceptable load. That is the function of all of the built-in ATUs in the Elecraft rigs. That protects the finals in the rig but did nothing to help the load the transmission line "sees". As the transmission line sees a higher and higher SWR, its losses increase. That load is determined by the antenna. And, when it is not practical to adjust the antenna for a good load at all frequencies, remote antenna tuners have become more common when transmission line losses are too large. Many, if not most, Hams simply live with the increased transmission line losses up to the point where their transmission line fails by being over-stressed with the excessive currents or excessive voltages produced by the standing waves on the transmission line. This occurs most commonly in the coaxial lines used by most Hams at QRO powers. 73, Ron AC7AC -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Drew AF2Z Sent: Thursday, August 31, 2017 7:17 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] Dusting off the old K3 & Considering a KAT3A An antenna current meter is pretty handy. I have a box of parts on my desk waiting to become one. At least when it shows zero current I'll be able to figure out pretty quickly that I forgot to connect the antenna, hehhe.. 73, Drew AF2Z On 08/31/17 18:09, Bill Frantz wrote: > Sorry Jim. You are indeed correct about the feedline SWR. While there > are other SWRs within the radio, they aren't of much interest. > > However, these radios do report a SWR in the UI, and that is what I > was referring to. Since a naive user might look at that figure and > say, "The SWR is 2. The antenna must be good.", it is important to > know that the tuners can produce a low figure on that meter with > nothing connected to the antenna connector. > > 73 Bill AE6JV > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to r...@elecraft.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
