TABLE OF CONTENTS Multiband vertical antennas have enjoyed considerable popularity with radio amateurs (including the author) because of their low angle of radiation and flexibility in changing bands without any form of external switching. Most of these multiband verticals have high degrees of inductive loading, and thus very narrow bandwidths on the 80- and 160-meter bands.
In order to obtain greater bandwidths on these bands and still maintain a multiband antenna system with a high degree of vertical radiation, a four-band (10-40 meters) trap vertical was connected, by the author, in parallel with sloper and inverted-L antennas for the 80-and 160-meter bands. This was done over a low-loss ground system of 100 radials, each about 50 to 60 feet in length. Impedance measurements (with the simple resistive bridge described in Chapter 12) showed that the sloper and inverted-L antennas had resonant impedances of 12 to 25 ?, depending upon: (A) the angle of slope (of the sloper), (B) the height of the vertical portion of the inverted L. and (C) the interaction between the 80- and 160-meter antennas. Since the inverted-L antennas were mounted 8 to 12 inches from the trap vertical, little difference was noted in the input impedance of the trap vertical (and hence performance). Slopers had very little effect since the capacitive coupling was minimal. Instead of using separate feed lines and matching transformers, or a single feed line and relays which switch to the appropriate matching transformers, parallel transformers were investigated for possible use. Two...
