I appreciate the contribution of the information found in the ARRL April 1962 QST article, which I have reviewed, and the technical parameters of impedance matching provided, however the information presented relates to the shortening of a 1/2 WL simple dipole from the resonant freq. terminal impedance of 72+j0 to achieve a terminal Z = 50-jXC and the subsequent removal of the XC component with a shunt XL Hairpin matching device. The gnd plane antenna in the original discussion has a 1/4 WL vertical radiating element terminal impedance of 36+j0. Any reduction of the length will result in a lower R component as well as to introduce shunt XC. If the 1/4 radiator was reduced in length proportionally as the 1/2 WL antenna was, it would have a terminal impedance of 50 divided by 72 or 0.694 times 36, resulting in a R component of about 25 Ohms. This is obviously is going the wrong way to achieve a suitable match for a 50 Ohm system. There is no way no how that the 36 Ohm 1/4 WL vertical radiator in a gnd plane antenna can be made to match 50 Ohms by the addition of a shunt XL component. Construction of the impedance on a Smith Chart verifies this. Only a series transmission line with a shunt reactance can get a impedance match to a 50 Ohm system. I would be happy to submit a Smith Chart with the appropriate series transmission line and location of the shunt stub illustrated. a. --- On Tue, 2/23/10, skipp025 <[email protected]> wrote:
From: skipp025 <[email protected]> Subject: [Repeater-Builder] Re: Ground plane yada yada To: [email protected] Date: Tuesday, February 23, 2010, 3:57 PM > "Al Wolfe" <k...@...> wrote: > > The straight skinny about the "beta" or "hairpin" match > can be found in a QST article, April 1962, by Gooch and > Gardiner. It explains how this matching scheme works. The > driven element is shortened making it capacitive. > Then the inductive reactance of the hairpin or beta > section re-resonates the element by canceling the > capacitive reactance of the shortened element while > raising the feedpoint impedance at the same time. Theory, > formulae, and practical examples are all in the article. > > The inverse is also desribed in the article where the element > is lengthened to make it inductive and a series capacitor > used to re-resonate the antenna. > > Both of these methods have been used for years to manipulate the > feedpoint impedence of an antenna. The beta does have the > advantage of presenting a DC ground. > > Al, K9SI Bingo and thank you Al. s.
