ARCHIBALD DOTY

Many years ago I built a 160 meter vertical antenna that consisted of approximately 120' of tower sections over an extensive 40 radial counterpoise about 6' above the ground... With the help of (SK) Harry Mills, K4HU and (SK) John Frey, W3ESU we finally determined that the major reason for this frequency change was that the capacity between the ground and the counterpoise was Acapacitive bottom loading@ the vertical, and thus reducing its resonant frequency. We subsequently reported some preliminary information on this phenomenon 1... Capacitive bottom loading, or ATuning@, of vertical antennas is certainly not a new concept. An application of it was discussed some years ago in an excellent QST article 2 and it is currently used in at least one commercial antenna 3. It is also shown, in an authoritative current antenna reference 4, on two drawings of 80 meter verticals. Here it is referred to (considering other parameters of the verticals) as being part of a Amatching network@.