I would suggest a more authoritative book "Electronic Applications of the Smith Chart, In Waveguide, Circuit, and Component Analysis" by Phillip H. Smith. In it Mr. Smith illustrates that no impedance matching can be achieved with only one component unless the "R" component of the impedance to be matched (Z=50+jX) is equal to the desired final impedance (Z=50+j0). In other words if the antenna (at resonance) has an impedance of Z=36+j0 (as in a 1/4 WL gnd plane antenna vertical) no amount of added series or parallel reactance will effect a resulting impedance having a pure 50 Ohm "R" component. Shortening the vertical radiator will result in the terminal Z to become lower in the "R" component as well as having a XC component, thus making a match impossible with a shunt inductance component. A much wiser approach would be to lengthen the vertical element till the "R" component is 50 Ohms (and the X component is inductive) and then add a S.C. transmission line in excess of 1/4 WL (to achieve the XC matching) and bond the S.C. end to the mounting pipe thus achieving a desired match as well as DC ground. I suspect the 1/4 gnd plane antenna that Skipp referenced had a vertical radiator longer than that required for resonance to raise the "R" component to 50 Ohms. The ARRL example uses a shortened 1/2 WL antenna simple dipole which will exhibit a lower (than the balanced resonant 72+j0 impedance) R-jX component. If the balanced dipole elements are shortened to achieve an impedance of 50-j50 then and only then will a shunt XL of 50 Ohms match to Z=50+j0. ARRL does not show how much shortening is required. In the 1960's Motorola introduced a new mobile antenna mount which had a better impedance BW (for a wider operating range) which included an insulator at the base made of Delrin for the express purpose of matching a vertical which was longer than required for resonance. The vertical had inductive reactance and was closer to the desired "R" component of 50 Ohms. a. --- On Mon, 2/22/10, BERNARD GNAT <[email protected]> wrote: From: BERNARD GNAT <[email protected]> Subject: db-201 measurements for 6 meters To: [email protected] Cc: [email protected] Date: Monday, February 22, 2010, 7:56 PM #yiv1482393875 #yiv317406957 #yiv1889239086 #yiv1060860581 {height:100%;color:#000000;font-size:12pt;font-family:Times New Roman;} Look in "ARRL ANTENNA BOOK " 1954 pages 109 and 110 . This may help in discussion. 73, Bernie
