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ANTENTOP- 02- 2004, # 006  

Multirange  Trap Antennas

 

 

SWR at 10 meters W1LNQ Antenna

 

 

Diagram Directivity and Input Impedance at 15 meters W1LNQ Antenna

 

 

impedance of the antenna at 10 meters is close to 40-Ohms, and50-Ohms coaxial cable can be used for feeding of the antenna at the range. However, physical length of antenna consisting of another following section plus the previously section (or sections) is less then λ/4. Inductors of the traps work as a lengthening spools for the proper section. Input impedance of the antenna working at lower then 10 meters range is less then 30 Ohms in the theory, but in practice, the input impedance for 15 and 20 meters range is close to 40 Ohms because losses in antenna parts and antenna

ground. So, a 50-Ohms coaxial cable can be used for feeding of the antenna at all of the ranges. For a proper work a vertical trap antenna must have several counterpoises for every of operation ranges, especially for low amateur HF ranges 40-, 80- and 160-m.

 

Antenna input impedance. Dipole Trap antenna:  Morgan trap antenna [1] was done as a dipole.  It is known, that a λ/2 (physical length) dipole antenna has input impedance close to 75 Ohms, see Figure 3A.  A shortened by a lengthening spool dipole

 

 

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