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NAVMARCORMARS COAXIAL CABLE TRAP DIPOLE FOR 3 & 5 MHZ

NAVMARCORMARS COAXIAL CABLE TRAP DIPOLE FOR 3 & 5 MHZ. THE CONCEPT – HOW IT WORKS. TRAPS ARE PARALLEL RESONANT CIRCUITS: PARALLEL CIRCUITS EXHIBIT VERY HIGH IMPEDANCE AT THE RESONANT FREQ. THE 5 MHZ DIPOLE DOESN’T “SEE” WIRE BEYOND THE POINT OF THE TRAP.

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NAVMARCORMARS COAXIAL CABLE TRAP DIPOLE FOR 3 & 5 MHZ

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  1. NAVMARCORMARS COAXIAL CABLE TRAP DIPOLE FOR 3 & 5 MHZ THE CONCEPT – HOW IT WORKS • TRAPS ARE PARALLEL RESONANT CIRCUITS: • PARALLEL CIRCUITS EXHIBIT VERY HIGH IMPEDANCE AT THE RESONANT FREQ. • THE 5 MHZ DIPOLE DOESN’T “SEE” WIRE BEYOND THE POINT OF THE TRAP. • THE 3 MHZ DIPOLE “SEES” THE ENTIRE LENGTH OF WIRE. • BOTH THE COIL AND CAPACITOR CAN BE MADE FROM THE SAME LENGTH OF COAXIAL • CABLE WOUND ON A LENGTH OF PVC PIPE : • THE CAPACITOR IS FORMED BY THE CAPACITANCE BETWEEN INNER AND OUTER CONDUCTORS OF THE COAX CABLE. • THE WINDING OF THE CABLE ON THE FORM ALSO CREATES AN INDUCTANCE.

  2. NAVMARCORMARS COAXIAL CABLE TRAP DIPOLE FOR 3 & 5 MHZ COAX CONNECTION DETAIL • THE COAX (RG-58/U IS WOUND ON A 1/8-IN PVC PIPE FORM 1-1/2 IN IN DIAMETER. • THE TRAP WILL RESONATE AT THE LOW END OF 5 MHZ WITH 13 TURNS OF • COAX CLOSE-WOUND ON THE FORM. • USE BRAIDED CENTER CONDUCTOR COAX VS SOLID –IT’S EASIER TO WORK WITH !

  3. NAVMARCORMARS COAXIAL CABLE TRAP DIPOLE FOR 3 & 5 MHZ THE LENGTH OF A HALF-WAVE DIPOLE IS CALCULATED BY THE FORMUA: 468 LENGTH IN FT = ------------------ F (MHZ) • CALCULATE THE LENGTH OF THE 5 MHZ DIPOLE FIRST: • 468 468 • L = ------------------- = ------------------ = 86.988 OR 87 FT • F (MHZ 5.380 MHZ • CONNECT 43.5 FEET OF WIRE TO EACH SIDE OF THE CENTER INSULATOR AND • THEN CONNECT THE TRAPS. • CALCULATE THE LENGTH OF THE 3 MHZ DIPOLE NEXT: • 468 468 • L = ----------------- = -------------------- = 143.1 OR 143 FT • F (MHZ) 3.270 MHZ • SUBTRACT THE LENGTH OF THE 5 MHZ DIPOLE FROM THE 3 MHZ DIPOLE: • 143 FT - 87FT = 56 FT • ADD 28 FEET OF WIRE FROM EACH OF THE TRAPS TO THE END INSULATORS.

  4. NAVMARCORMARS COAXIAL CABLE TRAP DIPOLE FOR 3 & 5 MHZ • TRIM THE DIPOLES TO THE DESIRED CENTER FREQUENCY AND LOWEST SWR. • START WITH THE 5MHZ DIPOLE THEN TRIM THE 3 MHZ DIPOLE. • TIP: PRUNE ONLY 6 INCHES OF WIRE AT A TIME. • EXACT LENGTH DEPENDS ON MANY FACTORS: • THE QUALITY OF THE COAX USED • THE HEIGHT OF THE DIPOLE ABOVE GROUND • NEARBY OBJECTS: HOUSE, TOWER, TREES, SWING SETS, ETC.

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