Dave, No, you are not an idiot, nor drunk, but you may be confused by the impedance transformation effects of a feedline. I suggest you take a look at the ARRL Handbook or Antenna Book chapter on Transmission Lines, especially the sections dealing with transmission line matching sections if you want an understanding of what is going on.
The most common feedline matching section used by radio amateurs is the quarter wavelength section - that one is relatively easy to understand and the math is not complex. The underlying mechanism is that a low impedance at one end will transform to a high impedance at the other end. For example, if a 50 ohm electrical quarter wave of coax is used and one end is connected to a 100 ohm load, the other end will have the equivalent of a 25 ohm load - and if the far end of that same coax is shorted, it will have a very high impedance (theoretically infinity, but practically >4000 ohms) at the near end Any length of feedline (and any impedance feedline) that is not matched in its characteristic impedance at the load will act as an impedance transformer. It is nice to know the resonance points for your antenna system, but what is really needed is the impedance (both resistive and reactive) at the desired frequencies of operation. If we knew all your feedline parameters (type, velocity factor, precise length, etc) we could likely compute the impedance at any other frequency, but it is easier to just measure it since your MFJ259 provides you with a tool to do exactly that. There is no impedance transformation on a transmission line (of any length) at the points where the antenna is matched to that line - that is the situation at your "resonance" points if you only looked at the SWR to determine resonance. The actual resonance point of the antenna *system* is where the reactance goes to zero (or very low as indicated on the MFJ259) - then at the resonance points you would look at the resistive component - it is not likely to be 50 ohms. One other piece of information that may help your 40 meter situation is based on the fact that you can use the tuner successfully at the balun location - and that is that an electrical half wavelength of transmission line will repeat the impedance at each end - so if you connect a total of a half wavelength transmission line between the tuner and the balun, the tuner will tune it. A 40 meter electrical half wave of solid dielectric coax will be in the vicinity of 42 feet (VF+0.66, and the length of the foam dielectric coax will be close to 55.5 feet (VF+0.84). The lengths you have been trying are closer to a quarter wavelength. 73, Don W3FPR djmd wrote: > I picked up an analyzer today (259B). It's my first one, and I hardly know > what I'm doing, but I can tell you right off the bat that whether I attach > it to the coax in the shack, or directly to the balun, it's appearing to be > resonant at the same 3 places. Around 10mhz, 20mhz, and 26mhz. If there is > any other information you would like to know from the analyzer at any > specific frequency and connnection point, please let me know. > > I hope this helps... I sincerely appreciate everyone's assistance. I'm still > learning and it's nice to have a place to get good info and not made to feel > like I'm an idiot. > :drunk::confused: > > ______________________________________________________________ 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
