" This program designs and calculates the performance of a trap dipole" "antenna. The basic approach taken here is the application of transmission" "line theory, including the effect of losses due to radiation. The antenna" "provides three specified operating frequencies but uses only a single pair"
"of traps. The traps are parallel inductor/capacitors tuned to the medium" "frequency in the usual manner, but are also constrained in L/C ratio to" "provide a specified higher harmonic operating frequency."
" At the low operating frequency the traps supply the correct amount of" "inductive reactance to bring the antenna into an equivalent electrical half" "wavelength condition. At the medium operating frequency the traps are" "anti-resonant, effectively preventing the outside portion of the antenna"
"from radiating. Thus the inner elements of the antenna form an electrical" "half wavelength at the medium frequancy."
" At the high harmonic operating frequency the traps have a small but" "significant capacitive reactance, somewhat reducing the electrical length"
"of the antenna, thereby requiring increased physical length."
" The lengths of the dipole elements given here assume negligibly short"
"leads at the traps and insulators, i.e. if the lead lengths at the"
"feedpoint and traps are unduly long, the elements must be shortened"
"accordingly."
" The velocity of propogation along the transmission line is taken as that"
"of free space. The lengthening effect due to fringing of the electrical"
"field at the ends of the antenna is handled as an equivalent end capacitor."
"The effects of losses and narrow-banding due to the loading traps show up"
"in the input impedance."
" Design calculations require an iterative routine which you must check for"
"convergence. Failure to converge implies you have asked for a physically"
" If you elect to design a conventional L/C trap, this program will ask you" "to input initial estimated specifications for the trap. These specs. can be" "obtained by running the HAMCALC L/C NETWORK TUNED CIRCUITS program. In that" "program, start with the L/C Tuned Circuit program, entering only your"
"lowest operating frequency and a reactance of about 180 ohms, as a jumping" "off point. (As a general rule-of-thumb, the reactance should be in the"
"order of 100 to 300 ohms). The program will calculate the value of"
"inductance required."
" Use the Inductor part of that program to select a coil and calculate the" "estimated Q of the L/C network. As an aid in selecting a coil you can call"
"up a catalog of standard B & W inductors from the menus of either this" "program or the L/C Network program."
" Enter the data obtained from the L/C Network program into this program." "This program will calculate final L/C data that you can check with the L/C" "Tuned Circuit program. By tiddling back and forth between the two programs" "you can fine tune the specifications for your traps. This may seem tedious," "but it is not nearly as tedious as several tower climbs with pruning shears" "in hand!"
