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How do Antenna traps work?
The trap dipole antenna uses a parallel resonant circuit or trap, that resonates on a particular frequency, thereby isolating a section of the antenna. This enables the inner section of the antenna to be used on the frequency where the trap resonates, and the whole antenna where it does not resonate.
How do you test an antenna trap?
“Grid-dip” meter method A simple way for the determination of the resonant frequency of a trap, or any tuned circuit is to connect a small section of wire forming a close loop, connected to the analyzer test port extension cable and put it near to or around the trap; see the Figure 1.
What is a trap in an antenna?
W hat is an Antenna Trap? A trap is a parallel tuned circuit (a capacitor in parallel w ith an inductor). Parallel tuned circuits (PTC) are used in all sorts of radio applications as they are selective: in this context a PTC has a resonant frequency at w hich it has a high impedance [1].
How do you measure resonance frequency of an antenna?
In common with other measurements for measuring the resonant frequency of a tuned circuit the basic idea is to couple the coil of the meter to the circuit under test. When the meter is tuned to the resonant frequency of the antenna then the meter current will dip.
What is a coaxial trap?
A coaxial cable trap is a parallel resonant circuit that is usually inserted in an antenna element to enable multiband operation. Since coaxial cable is always designed for outside use, the trap is inherently weather-resistant, except for the connections at the ends.
How does a 21 MHz antenna trap work?
When a Tri-band 10, 15 and 20 meter beam is excited with 21 MHZ energy only the length of element to the 21 MHZ trap is used. The trap is situated 1/4 wave length from the boom of a yagi and is similar to that of an open switch.
How does the length of an antenna wire depend on the trap?
The length of wire beyond the trap depends on the two basic frequencies at which the antenna is designed to operate. It is required that the trap’s input impedance should be as high as possible over a relatively narrow band of frequencies which depends on the L/C ratio of the trap.
How does an antenna trap on a Yagi work?
The trap is situated 1/4 wave length from the boom of a yagi and is similar to that of an open switch. The same electric circuit is present on 10 meters. Conversely, the 14 MHZ signal perceives the 21 and 28 MHZ traps as a closed switches at 14 MHZ. The 20 meter signal and uses the whole length of the element.
How is the length of a sleeve antenna determined?
A simple way to begin the design process is to start with the symmetrical sleeve antenna where both antenna elements are equal to each other, each being λ/4. This length can be determined from where v is the velocity of signal propagation in a coax, and f0= 222.5 MHz.